8 doz. eggs
12 lbs. sugar
3 „ cocoa or chocolate
5 „ assorted fruits that do not pulp
2 „ seeded raisins
3 „ dates
4 „ walnut meats
4 tablespoonfuls ground cinnamon
1 „ ginger
1 „ ground cloves
Use the eggs as directed under receipt No. 1. Chop the fruits and nuts
fine.
Receipt No. 3.--Fruit Pudding
32 lbs. 10 per cent cream
8 „ whole condensed milk
8 „ sugar
5 oz. gelatine dissolved in part of cream
2 lbs. chopped cherries
2 „ „ raisins
2 „ „ nuts
1¹⁄₂ qts. sherry wine
Soak the fruit overnight in sherry wine.
Receipt No. 4.--Manhattan Pudding[19]
[19] Ia. Bul. No. 123.
3 gals. 30 per cent cream
10 doz. eggs
12 lbs. sugar
2 qts. orange juice
1 pt. lemon juice
4 lbs. walnut meats
4 „ pecan meats
4 „ cherries and assorted fruits
=73. Custards.=--A custard is usually made of milk, sugar, flavoring,
cornstarch or flour and the process is rather long. Quantities given
in receipts are for hand freezers.
Receipt No. 1.
6 qts. milk
3 lbs. sugar
24 eggs
12 tablespoonfuls cornstarch
6 „ vanilla or to taste
Put the milk over the fire in a farina or double water boiler. Moisten
the cornstarch with a little cold milk so that it can be added to milk
without lumping. When the milk is hot, add the cornstarch and stir
until it begins to thicken. Beat the eggs and sugar together until
light and then add them to the hot milk. Cook a few minutes, take from
the fire, flavor and cool and freeze same as ice-cream.
Other flavors, as coffee or chocolate, may be made by substituting
these flavors for the vanilla.
Receipt No. 2.
5 qts. milk
1 qt. 30 per cent cream
8 eggs
2¹⁄₂ lbs. sugar
6 tablespoonfuls flour
1¹⁄₂ oz. of vanilla or to taste
Follow directions given for No. 1.
Receipt No. 3.
2 qts. 30 per cent cream
4 „ milk
3 lbs. sugar
1¹⁄₂ qts. minute tapioca
Yolks of 4 eggs
1 teaspoonful salt
4 teaspoonfuls lemon extract
2 teaspoonfuls rose extract
Cook the tapioca in 2 quarts of milk for ten minutes, then add the
remainder of the milk, the sugar and the salt. Cook ten minutes longer.
Remove from the fire and add the egg-yolks well beaten. Then add the
extract, cool and freeze. When nearly done add the cream previously
beaten to stiff froth and finish freezing. A large number of receipts
for custard ice-cream may be found in the various cook-books.
=74. Ices and sherbets= are usually made either of water or milk, with
or without eggs and flavoring. Some kinds are frozen without agitation
and some beaten like ice-cream while freezing.
=75. Ices= are simply water sweetened, flavored and frozen. They become
grainy in texture very quickly.
Receipt No. 1.
48 lbs. water
20 „ sugar
6 „ lemon juice
Receipt No. 2.
48 lbs. water
20 „ sugar
2 „ lemon juice
4 qts. pineapple juice
Receipt No. 3.
48 lbs. water
20 „ sugar
2 „ lemon juice
4 qts. finely pulped strawberries
=76. Water sherbet.=--The only difference between water sherbet and
ices is that eggs are used in the former and not in the latter.
Receipt No. 1.
48 lbs. water
16 „ sugar
1 lb. lemon juice
4 qts. grated pineapple (or pineapple juice)
6 oz. gelatine in 4 lbs. water, if desired
24 egg-whites beaten stiff and added when mixture is partly frozen
Receipt No. 2. Same as No. 1 except replace the pineapple with grape
juice.
Receipt No. 3. Use same mix as No. 1 except replace the pineapple with
orange juice. Boil the water and sugar to a clear sirup, then strain
and cool before freezing.
=77. Punches.=--The essential difference between ices, water sherbets
and punches, is the material used for flavoring.
Receipt No. 1.
48 lbs. water
20 lbs. sugar
1 „ lemon juice
1 qt. brandy and rum mixed
Receipt No. 2.
48 lbs. water
20 „ sugar
1 lb. lemon juice
1 qt. orange juice
2 qts. wine
4 oz. gelatin in part of water
Receipt No. 3.
48 lbs. water
20 „ sugar
1 qt. lemon juice
1 „ raspberry juice
1 „ grape juice
cloves, cinnamon, allspice, and nutmeg to taste
=78. Milk sherbets.=--These are similar to water sherbets except milk
is used in place of water.
Receipt:
48 lbs. milk
16 „ sugar
5 ozs. gelatine in 2 qts. water
1 lb. lemon juice
4 qts. fruit flavoring
12 egg-whites beaten stiff and added after mixture is partly frozen
Flavors: Orange, grape, cherry, pineapple, and strawberry. If lemon is
desired, use only 2 quarts of lemon juice with 1 quart of orange juice.
=79. Lacto[20].=--This is the only receipt in which sour milk is used.
[20] Ia. Exp. Sta. Bul. No. 140.
Receipt:
48 lbs. good starter just nicely coagulated
18 „ sugar
24 eggs, whites and yolks beaten separately
2 qts. grape juice
1¹⁄₂ qts. lemon juice
Mix in the order given in the formula. Other flavors may be substituted
for the grape juice.
CHAPTER VII
_EQUIPMENT_
The size and kind of equipment will depend on the extent of the
business and the available capital. It is not considered economical to
install a mechanical refrigerating system unless at least seventy-five
gallons of ice-cream are manufactured a day.
Certain factors should be considered when purchasing machinery; the
construction and adaptability of the machine for the type of work it is
intended to do; the ease of making repairs; the ease of cleaning; the
durability of the machine; the protection to gearing from ice and salt.
[Illustration: FIG. 8.--Hand freezer with tub and can cut away showing
ice and salt mixture and beaters and scrapers in the can.]
[Illustration: FIG. 9.--Hand freezer with fly wheel, using salt and ice
mixture for freezing. The capacity is five gallons.]
[Illustration: FIG. 10.--Power driven tub and can freezer, using a salt
and ice mixture. The can, dasher, cover and gears are shown removed.]
[Illustration: FIG. 11.--Horizontal brine freezer attached to salt and
ice brine box. The pump is behind the box.]
=80. Freezers.=--The general principle of the ice-cream freezer is
the same in all makes; however, the application may be varied. The
unfrozen ice-cream or mix is placed in a container, usually called the
freezing-can. This can is surrounded by the freezing material, either
cold circulating brine or an ice and salt mixture. In the can is the
beater or dasher. To this is attached two scrapers which, when rotated,
scrape the frozen ice-cream from the sides. The can itself may revolve
or stand still, depending on the type of freezer. The dasher may
revolve or stand still, depending on whether the can revolves or stands
still. In most freezers there is another part of the dasher which
revolves to help beat up the ice-cream. The freezers may be divided
into two general classes. The one class consists of a tub and can in
which an ice and salt mixture is used between the tub and can. This
type of freezer is made to run by hand or mechanical power, and varies
in size from a few pints to ten gallons. The largest hand size is
usually five gallons; these have a flywheel. The types of hand freezers
are shown in Figs. 8 and 9. A power-driven tub and can freezer, using
a salt and ice mixture in the tub for freezing, is shown in Fig. 10.
The other class is the brine freezer. In this, cold brine is forced
around the freezing-can. The freezer runs by mechanical power, either
belt-driven or directly connected to an electric motor. The brine
may be made from an ice and salt mixture, or it may be cooled by an
artificial refrigerating system. There are two general types of brine
freezers. One has the freezer in a horizontal position and the other
in a vertical. Advantages are claimed for both. The arrangement of
brine freezers when the brine is obtained from a salt and ice mixture
is shown in Figs. 11 and 12. The brine as it comes from the freezer is
sprayed over the ice and as it trickles through is cooled again. It is
then pumped around the freezer again. The ice is held in the box by
means of a heavy wire screen; otherwise, it would clog the pump.
[Illustration: FIG. 12.--Vertical belt driven brine freezer connected
to ice and salt brine box. Pump is shown between freezer and box.]
[Illustration: FIG. 13.--Perfection brine freezer, direct motor drive.]
Some of the types of brine freezers in common use are shown in Figs.
13, 14, 15, and 16. Most of these may be either belt or direct
motor-driven. The usual size is ten gallons. In some cases they have
been made larger but these are not in common use. It is the usual
practice to have a supply tank just above the freezer-can which can
be filled, while one can is freezing. The mix for the next freezer is
placed in this supply can and will then run quickly from it into the
freezer.
[Illustration: FIG. 14.--Progress vertical belt drive brine freezer.]
[Illustration: FIG. 15.--Emery Thompson vertical direct motor drive
brine freezer.]
Another brine freezer is the disc which may be used either as a batch
or continuous freezer. A front view of this is shown in Fig. 17. The
supply can is seen on one side and the delivery spout on the other. A
glass plate over the freezing discs allows the process to be seen at
any time. A side view is seen in Fig. 18, showing the brine box and
pump. The freezing discs are illustrated in Fig. 19, also the scrapers
to remove the ice-cream from the discs and the screw to force the
ice-cream along. When used as a batch freezer, the ice-cream is drawn
from the bottom.
[Illustration: FIG. 16.--Fort Atkinson horizontal belt drive brine
freezer.]
[Illustration: FIG. 17.--Disc brine freezer either continuous or batch.]
[Illustration: FIG. 18.--Side view of freezer shown in Fig. 17.
Arrangement of brine tank and pump are shown.]
[Illustration: FIG. 19.--Freezing discs of freezer shown in Figs. 17
and 18. The scrapers for removing the ice-cream from the discs and the
screw to force it out of the delivery spout are shown.]
[Illustration: FIG. 20.--A pasteurizer or ripener used as an ice-cream
mixer. Strips are attached to the coils to prevent the settling of the
sugar on the bottom.]
=81. Mixers.=--When large quantities of ice-cream are made, a
container of some sort, with a mechanical agitator to stir the
contents, is used to mix the ice-cream ingredients. Some of these
mixers are provided with coils in which water or brine may be
circulated to control the temperature. Some may be operated as a
pasteurizer. An ordinary cream ripener might be used as a mixer if
the sugar could be prevented from settling to the bottom. Some
manufacturers have accomplished this by placing a strip of iron on
the coils which will reach almost to the bottom of the ripener. Such
an arrangement is shown in Fig. 20. An ordinary starter can might be
utilized as a mixing vat or can. (Fig. 21.)
[Illustration: FIG. 21.--Minnetonna starter can or ice-cream mixer.]
A number of ice-cream mixers are commonly used, as shown in Figs. 22,
23, and 24. Most of these have coils which carry cold water or brine
to cool the mix. In some these coils act as the agitator and in others
they are placed in a jacket around the mixer. In order to keep the
materials properly mixed if the coils themselves do not serve as the
agitator, there is some form of mechanical agitator. These agitators
may be belt or direct motor-driven.
=82. Gelatine kettles.=--In most plants where much ice-cream is made,
a special kettle is employed to dissolve the gelatine. (Fig. 7.) This
consists of a copper steam-jacketed kettle. With this the gelatine
and water may be heated without danger of burning. The size of these
kettles depends on the amount of gelatine used.
=83. Hardening the ice-cream.=--Some means of keeping the ice-cream
cold after it is removed from the freezer must be provided. This may be
a specially cooled room known as a hardening room or the ice-cream may
be packed in a mixture of salt and ice. These methods of hardening will
be discussed later.
[Illustration: FIG. 22.--Alaska ice-cream mixer. The side is cut away
showing the coils and insulation. The mechanical agitator is seen at
the bottom. By means of the tight fitting cover and the air pump, the
mix may be forced to the freezer by air pressure.]
[Illustration: FIG. 23.--Wizard ice-cream mixer.]
[Illustration: FIG. 24.--Emery Thompson ice-cream mixer.]
=84. Packing-cans.=--In order that the freezer may be kept in use,
as soon as the ice-cream is sufficiently frozen, it is removed and
placed in other cans to harden. These are known as packing-cans (Fig.
25) and are made of heavy iron and tinned and fitted with a cover. The
cans vary in size from one quart to five gallons and the ice-cream
is hardened and delivered in these. When ready for delivery, these
pack-cans are placed in tubs which should be a little higher than the
pack-can to allow for ice over the top. There should be a space also of
2-4 inches between the sides of the can and the tub to allow for the
ice and salt. The ice-cream may be packed in small oblong containers
known as bricks, usually containing one or two pints.
[Illustration: FIG. 25.--Two types of ice-cream packing-cans.]
The ice-cream may be hardened in a larger brick mold which will make
several smaller bricks. When hard the ice-cream is cut into the smaller
bricks, wrapped in parchment paper and placed in a paper carton. This
is the usual method of handling brick ice-cream. Several different
layers may be placed in each brick.
=85. Ice crushers.=--The ice must be broken into small pieces for
freezing or packing the ice-cream. This may be done by hand with an ice
spud or cracker. (Figs. 26 and 27.) If much ice is to be cracked or
crushed, a mechanical crusher should be used. (Fig. 29.) The small ones
run by hand power but turn rather hard. The crushers run by mechanical
power are more frequently seen in ice-cream plants. These vary in size.
[Illustration: FIG. 26.--Ice spud.]
[Illustration: FIG. 27.--Ice cracker.]
[Illustration: FIG. 28.--Perforated ice shovel.]
[Illustration: FIG. 29.--Ice crusher with tight and loose pulley for
mechanical power. The teeth or picks on the drum may be seen.]
[Illustration: FIG. 30.--The perfection ice-cream can-washer and
sterilizer.]
=86. Ice-cream can-washers.=--The washing of the ice-cream pack-cans
by hand in an ordinary sink consumes much time. In the larger plants
an ice-cream can-washer is used. This consists of sprays of water and
revolving brushes. The cans are usually brushed both on the inside and
outside. Some types of ice-cream can-washers and sterilizers are shown
in Figs. 30 and 31. When washed, the cans should be sterilized.
[Illustration: FIG. 31.--Fort Atkinson ice-cream can-washer and
sterilizer.]
[Illustration: FIG. 32.--De Laval centrifugal emulsor.]
=87. Emulsors, creamers, and homogenizers.=--These machines vary
considerably in mechanical construction as shown in Figs. 32, 33,
34, 35, and 36. Nevertheless, the making of cream from butter, milk
powder, condensed milk or skim-milk is accomplished by each machine.
The force used to break up and mix the materials varies with the
different machines. One type which uses steam as the force to break up
the material is illustrated by Fig. 33. The amount of steam pressure
required varies with the different makes. Another type of machine which
uses centrifugal force as the means of breaking up the materials is
illustrated by Figs. 32 and 36. In this type, the materials are broken
up or mixed by being thrown by centrifugal force through a very small
opening or narrow space. The other type of machine, which is operated
by valve pumps, is illustrated in Figs. 34 and 35. By means of the
pumps the materials are forced through a very small opening against
some hard material. This machine, known as a homogenizer, breaks the
materials into very small particles; for example, cream that has been
homogenized cannot be re-churned in butter because of this. A good
quality of cream may be made from any of the following combinations
according to the DeLaval Separator Company:
Skim-milk powder--water--butter--(preferably uncolored and unsalted).
Whole-milk powder--water--butter.
Condensed skim-milk--water--butter.
Condensed whole milk--water--butter.
Skim-milk--skim-milk powder--butter.
Skim-milk--condensed skim-milk--butter.
Whole milk--skim-milk powder--butter.
Whole milk--condensed skim-milk--butter.
[Illustration: FIG. 33.--Perfection cream-maker and emulsifier.]
[Illustration: FIG. 34.--Progress homogenizer.]
[Illustration: FIG. 35.--Gaulin homogenizer.]
One should never lose sight of the fact that the better the quality of
the materials used, the better will be the flavor of the cream. It is
impossible to make first-quality cream from poor materials. The whole
milk and skim-milk must be clean and sweet. Skim-milk powder should be
dry, loose, and fluffy. The condensed milk should be clean flavored
and fresh. Off-flavored condensed milk or milk that is grainy or gritty
should never be used. The manufacturers of the various machines send
specific directions for their operation. To insure success, these
directions should be followed carefully. It is the usual practice
first to put the milk powder into solution, then to cut the butter
into small pieces and put it into the milk. If skim-milk is used, the
butter is put directly into it. The milk and butter are then heated to
a temperature high enough to melt the butter, usually 130° to 150° F.
It is then run into the machine. Because of the tendency of the butter
to rise to the top, the materials must be kept in constant agitation
until run into the machine. Otherwise, the butter would be at the top
and would not run into the machine until the other materials had all
run through.
[Illustration: FIG. 36.--Sharples centrifugal emulsor.]
Some makers emulsify or homogenize the whole ice-cream mix. In this
case, the flavoring extracts and fruits are not added until after the
mix has been through the machine. It is the general opinion that the
emulsifying or homogenizing of the whole mix makes a smoother body and
texture in the product.
Advantages in the use of emulsors and homogenizers:
1. Smoother body in ice-cream.
2. Less time required for ageing cream, especially pasteurized.
3. Not necessary to carry so large a stock of raw materials.
4. Ice-cream of more uniform composition.
Disadvantages in the use of emulsors and homogenizers:
1. The disadvantage in the use of the homogenizer is in its abuse
since a homogenized cream will appear richer than it really is. There
is a tendency to use less solids, especially fat.
2. Danger of using inferior materials.
3. If cream is not needed for ice-cream and has been homogenized, it
cannot be churned.
=88. Cost of equipment.=--Because of the constant change in price, it
is impossible to give even estimates of cost of equipment. The price
might be correct to-day and incorrect to-morrow. The cost of equipment
based on the gallonage of ice-cream is usually higher for the smaller
plant. In order to obtain accurate prices, the various dairy supply
houses should be consulted.
CHAPTER VIII
_REFRIGERATION AS APPLIED TO ICE-CREAM-MAKING_
In the making of ice-cream, refrigeration is necessary. In the
following discussion only the underlying principles as applied to
operation will be taken up. The details of construction are discussed
by refrigerating engineers in various text-books.[21]
[21] Audels, “Answers on refrigeration,” 700 pages; Cooper, Madison,
“Practical cold storage,” 800 pages.
Refrigeration is the interchange of heat units. The cooling for
ice-cream-making may be obtained either from natural ice or from
mechanical refrigerating machines. These will be discussed under their
separate heads.
=89. Terms used.=--In order easily to comprehend the principles of
refrigeration, it is necessary to understand the terms used.[22]
[22] Bowen, John T., “The application of refrigeration to the handling
of milk,” U. S. Dept. Agr. B. A. I., Bul. 98.
“British thermal unit.--A British thermal unit (B. T. U.) is the
quantity of heat required to raise 1 pound of pure water 1 degree
Fahrenheit, at or near its maximum density, 39.1° F. Some authorities
consider a British thermal unit as the heat required to raise 1 pound
of pure water from 61° to 62° F. For practical purposes, however, it
may be considered the heat required to raise the temperature of 1 pound
of water 1 degree Fahrenheit.
“Sensible heat.--Sensible heat is the heat that may be felt by the hand
or measured by a thermometer.
“Latent heat.--Latent or ‘hidden’ heat is the heat which is expended
in molecular work of separating the molecules of the substance and can
not be measured by a thermometer. Every substance has a latent heat of
fusion, required to convert it from a solid to a liquid, and another,
latent heat of vaporization, required to convert it from a liquid to
a gas or vapor. Thus, if heat is applied to a pound of ice at 32° F.
it will begin to melt, and no matter how much heat is applied, the ice
will not get any hotter. After every particle of ice has melted, we
will have 1 pound of water at 32° F., the same temperature as the ice
before heat was applied. Experiments have shown that it requires 144
British thermal units to melt 1 pound of ice at 32° F. into water at
32° F.; hence the latent heat of fusion of ice is said to be 144.
“If heat is applied to 1 pound of water at 212° F., the water will
remain at 212° F. under atmospheric pressure until all of it has been
evaporated into steam at 212° F. This has been found to require 970.4
British thermal units; hence the latent heat of vaporization of steam
at atmospheric pressure is said to be 970.4 B. T. U.
“Specific heat.--The specific heat of a substance may be defined as the
ability of that substance to absorb heat compared to that of water.
Water being one of the hardest of all substances to heat, its specific
heat is taken at unity. A better understanding of latent and specific
heat may be had by studying the diagram in figure 42 which shows
graphically the relation of heat to temperature.
“Ton refrigeration.--Refrigeration, or ice-melting capacity, is a term
applied to represent the cold produced, and is measured by the latent
heat of fusion of ice, which is 144 B. T. U. per pound. In other words,
it is the heat required to melt 1 pound of ice at 32° F. into water
at the same temperature. The capacity of a machine in tons of ‘ice
melting’ or ‘refrigeration’ does not mean that the machine would make
that amount of ice, but that the cold produced is equivalent to the
melting of the weight of ice at 32° into water at the same temperature.
Therefore 1-ton refrigeration is equal to 144 × 2,000, or 288,000 B.
T. U. A 1-ton refrigerating machine is a machine that has a capacity
sufficient to extract from an insulated bath of brine 200 B. T. U. per
minute, 12,000 B. T. U. per hour, or 288,000 B. T. U. per 24 hours.
“Absolute pressure.--Absolute pressure is pressure reckoned from
a vacuum. Pressure gauges in general use are arranged to indicate
pressure in pounds per square inch above atmospheric. To convert gauge
pressure to absolute pressure, 14.7 pounds, the weight per square inch
of air pressure at sea level, must be added.”
NATURAL ICE
Only in the cold or northern latitudes can a supply of natural ice be
obtained. In the warm regions a refrigerating machine or ice made by
an artificial refrigerating system must be used. The harvesting of ice
is a very simple process, yet it involves a large number of details.
Success in obtaining a crop of ice requires careful attention to each
detail.
=90. The ice field.=--It is important that the water from which the
ice is to be made be free from contamination. If weeds grow in the
pond in the summer, they should be removed in the fall. If green spawn
or algæ grow profusely, they can be eliminated by the use of copper
sulfate.[23] The crystals may be placed in a cloth sack, which is
hung to a pole and trailed through the water until the salts are
dissolved. One or two treatments of the sulfate in the season, at
the rate of 1 pound to 100,000 gallons (13,000 cubic feet) of water
will be sufficient to keep down such growth and make the water clear
and pure. The area of the ice field or pond should be large enough
to fill the ice-house at a single cutting, some allowance being made
for waste. The water should be deep enough so that there will be at
least from eighteen inches to two feet under the ice at the time of
harvesting. Snow often interferes with the ice formation. If the ice
is thin, and the fall of snow heavy, the latter may sink the ice. If
the snow remains on the ice, it acts as an insulator and so prevents
the freezing. The snow may be handled in either of two ways; it may be
scraped off the ice by hand or with a horse scraper, or the snow may be
soaked with water. In the latter practice, there is danger of a crust
forming and so preventing the formation of ice and hindering future
scraping.
[23] Corbett, L. C., “Ice houses,” U. S. Dept. Agr., Farmers Bul. 475,
1915.
=91. The ice-house.=--The main essentials of a good ice-house are
insulation, ventilation, and drainage. The house should be so located
that there will be good drainage. If proper drainage is not provided,
the water acts as a conductor of heat and so causes the ice to melt
faster. It is desirable, but not necessary, that the ice-house have a
north exposure and shaded with trees to keep off the heat of the sun.
It should be located as near the place where the ice will be used as
possible. There is a wide range of variation in type of construction
and cost of materials in the erection of a satisfactory ice-house. The
walls may be insulated so that the ice is simply piled in the house.
This is the most expensive type of construction. In contrast to the
insulated house, a bin may be built and the cakes of ice piled close
together in it so that there will be a space about one foot to eighteen
inches around the sides between the ice and the bin. This space should
be filled with sawdust or hay and an equal amount placed over the top,
which acts as an insulator. This is the cheapest form of construction
and is somewhat wasteful since the top of the pile is exposed to the
direct rays of the sun and the rains. The usual type of ice-house is
a form of construction between the two extremes mentioned above. It
consists of a cheap board frame to hold the insulation on the sides and
a roof. The gables should be partly open to give a circulation of air.
A cubic foot of ice weighs about 58 pounds and requires about 35
cubic feet for a ton. Allowance for the spaces between the cakes of
ice should be made when figuring the capacity of the house. The usual
practice is to figure from 43-46 cubic feet for each ton of ice.
=92. Harvesting and storing.=--Ice is not usually harvested until at
least 8-12 inches thick. This will depend on the location and the
season. The size of the cakes vary, but the usual sizes are 22 × 32
inches; 20-22 × 28; 22 × 42-44. The cakes of ice may be sawed with a
hand-saw. (Fig. 37.)
On a large field, the ice may be cut with an ice-plow drawn by horses.
(Fig. 38.) On this plow is a marker to show where the next cut should
come. Thus if the first cut is straight, a straight mark will be made
to be followed for each succeeding cut. The ice-plow does not cut
entirely through the ice, but it should be adjusted to cut nearly
through. This will make the breaking off of the cakes easy. If the
field is large enough, it is usually plowed each way. This cuts the
ice into cakes. Therefore, after plowing all that is necessary is to
separate the cakes. This is accomplished by breaking or splitting with
a splitting-fork. (Fig. 39.) On a small field, the ice is sometimes
plowed only one way. In this case the cakes are sawed off with the
hand-saw.
[Illustration: FIG. 37.--Hand ice-saw.]
[Illustration: FIG. 38.--Ice-plow with marker.]
Either a perpendicular or inclined elevation with their conveyors
should be used to put the ice into the house. Only regular shaped
cakes should be stored, all broken ones being rejected because they do
not pack closely, hence allow too much waste and air space. The cakes
should be packed closely together and yet allow air circulation. In
order to secure this, it is best to run the rows of cakes one way in
one tier, the other way in the next tier and so on. Each tier should
be planed smooth before the next is placed on it. This may be done
by a large planer on the ice incline or by hand in the house. The
insulation should be put around the sides as the house is filled. When
all the ice is in the house, the insulation, either hay or sawdust,
should be immediately placed over the top. The ice should be watched
and if the hay or sawdust has settled so that the ice is exposed to
the air, more should be added. It is best to fill the house when it is
freezing temperature. If it is thawing the cakes of ice will have water
on them, later this will freeze and it will be almost impossible to
remove the cakes without breaking them. When taking the ice out, each
tier should first be removed before the one below is disturbed. After
each removal of ice the covering over the top should be replaced.
[Illustration: FIG. 39.--Splitting fork.]
=93. Amount of ice needed.=--It is difficult to know exactly how much
ice to store to meet the needs of the summer. Some ice goes farther
than others; some years there is more waste than others. The following
figures compiled by the “Ice Cream Trade Journal” will give a fair idea
of the amount required to a gallon of ice-cream: Amount of ice used for
100 gallons, 1,928 pounds. This was divided as follows: freezing, 614
pounds; hardening and storing, 914 pounds; shipping, delivering, and
icing cabinets, 400 pounds.
=94. Use of ice and salt mixture.=--Under normal conditions ice melts
slowly. In order to obtain a quick change of temperature and one below
that of the ice, a salt and ice mixture is used. Bowen[24] gives the
following discussion of cooling by salt and ice mixtures: “When two
solid bodies, as salt and ice, mix to form a liquid a certain amount
of heat becomes latent, called the latent heat of solution. Since this
latent heat is taken from the mixture itself the temperature falls
correspondingly. The temperature obtained by a salt and ice mixture
depends principally on the relative proportions of the mixture, and
to a less extent on the rate at which the heat is supplied from the
outside, the size of the ice lumps and salt particles, and the amount
and density of the resulting brine. Hence it is impracticable to give
other than approximate temperatures with fixed ratios of salt and
ice. The following curve (Fig. 40) shows the approximate temperature
obtained with different proportions of salt and ice.
[24] Bowen, John T., “The application of refrigeration to the handling
of milk,” U. S. Dept. Agr. B. A. I., Bul. 98.
[Illustration: FIG. 40.--Approximate temperatures obtained with
different proportions of ice and salt.]
“One pound of ice, in melting, absorbs 144 B. T. U. This is known as
the latent heat of fusion of ice. Salt in dissolving also absorbs heat,
called the latent heat of solution, which varies in amount, depending
on the density and temperature of the resulting brine.
“The heat of solution of salt in water at 32° F. varies from 58 to 16
B. T. U., depending on the final strength of the brine obtained.
“The following curve (Fig. 41) shows the amount of refrigeration
available per pound of ice and salt mixture. The figures were
calculated from the melting of ice at 32° F. into a liquid at the same
temperature. If, however, the salt is added to the ice at a temperature
varying from 32° F. or, if the resulting brine is allowed to escape at
a temperature other than 32° F., the amount of available refrigeration
must be corrected accordingly. These corrections are determined by
multiplying weights, in pounds of salt and brine, by their respective
specific heats and by their difference in temperature from 32° F. The
specific heat of dry salt may be taken as 0.214, as the specific heat
of salt brine varies with its density.
[Illustration: FIG. 41.--Refrigeration available with different
percentages of salt.]
“Usually salt when added to ice is of a higher temperature than that of
the ice; consequently the correction for its heat above 32° F. must be
subtracted from the available refrigeration shown by the curve, Fig.
41; and if the brine is allowed to escape at a temperature below 32°
F. the refrigeration lost in the discharge brine must be subtracted,
while, on the other hand, if the discharge brine is at a temperature
higher than 32° F. the correction must be added.
“If given amounts of ice and salt, at a temperature of 32° F. are mixed
together and the mixture supplied with sufficient heat to melt the
ice and dissolve the salt and raise the temperature of the resulting
brine to the original temperature of 32° F., then the total amount of
heat absorbed by the reaction will be the sum of the latent heat of
the ice and the heat of solution of the salt to form the resulting
brine of the density which will result from the particular proportion
of salt and ice chosen. As an example, under the foregoing conditions,
if 100 pounds of dry salt are added to 900 pounds of ice the total
available refrigeration is 1,000 × 133 = 133,000 B. T. U. The available
refrigeration per pound of mixture, 133 B. T. U., is taken from the
curve in Fig. 41. If the salt added is at a higher temperature than
32° F., say 60° F., then the available refrigeration will be 133,000
- [100 × 0.214 (60 - 32)] = 132,401 B. T. U., or 132.4 B. T. U. per
pound of mixture. If the resulting brine is allowed to escape at 25°
F., the available refrigeration is 133,000 - [1,000 × 0.892 (32 - 25)]
= 126,756 B. T. U., or 126.7 B. T. U. per pound of mixture. Or, in
other words, there is lost in the first case 100 × 0.214 (60 - 32) =
599 B. T. U., and in the second case, 1,000 × 0.892 (32 - 25) = 6,244
B. T. U., or a total loss, if the salt is added at 60° F. and the brine
allowed to escape at 25° F., of 599 + 6,244 = 6,843 B. T. U. Under
these conditions the available refrigeration is 133,000 - 6,843 =
126,157 B. T. U., or 126 B. T. U. per pound of mixture.”
MECHANICAL REFRIGERATION
A large number of small ice-cream plants do not use mechanical
refrigeration, but natural ice. It is not considered economical
either in labor or cost to attempt to employ ice if seventy-five or
more gallons of ice-cream are made a day. The size of the mechanical
refrigerating machine varies, but the underlying principles are the
same.
=95. Principles of mechanical refrigeration.=--Bowen gives the
following concise but plain description of these principles:[25]
[25] Bowen, J. T., “The application of refrigeration to the handling of
milk,” U. S. Dept. Agr. B. A. I., Bul. 98.
“When a solid or a liquid changes its state or condition, as when a
solid is converted into a liquid or a liquid into a gas or vapor,
the change of state or condition is in each case accompanied by the
absorption of heat. This absorption of heat, as previously explained,
is called ‘Latent Heat’; that is, heat that cannot be measured by a
thermometer; and in order to transfer a substance from one state to
another it is only necessary to supply or extract heat. For instance,
if we take 1 pound of ice at zero temperature, Fahrenheit scale, and
apply heat, the temperature will rise until it reaches 32°. If we
continue the application of heat, the ice will begin to melt, and after
we have supplied sufficient heat the 1 pound of ice will have changed
to water at 32° F., the same temperature at which the ice commenced
to melt. If the application of heat is continued the water will grow
warmer, but at a slower rate. It now takes about double the amount of
heat to raise the 1 pound 1 degree as water that it did to raise the 1
pound 1 degree as ice. In other words, the specific heat of water is
approximately double that of ice.
“When sufficient heat has been added to raise the 1 pound of water to
a temperature of 212° F., another critical point is reached at which
further application of heat to the water, under atmospheric pressure,
will not increase its temperature, but changes it into steam at a
temperature of 212°. The relation of heat to temperature is shown in
Fig. 42.
“It will be noted from Fig. 42 that to raise the temperature of the 1
pound of ice from zero to the melting point (32° F.) 16 B. T. U. were
expended; in melting the ice, 144 B. T. U.; in raising the water to the
boiling point, 180 B. T. U.; and to evaporate the water, 970.4 B. T. U.
If the operation is reversed, the heat being extracted instead of being
added, the curve will follow backward on itself to the starting point.
“The latent heat of fusion and the latent heat of vaporization are
represented on the diagram by the two lines parallel to the horizontal
base line, the length of the lines representing to scale the amount
of heat expended in molecular work in separating the molecules of the
substances. Starting from the left, the rising lines represent the
heat required to raise the temperature of the ice, water, steam at
constant volume, and steam at constant pressure, respectively.”
[Illustration: FIG. 42.--Diagram showing relation of heat to
temperature.]
=96. Materials used in mechanical refrigerating systems.=--“The same
law applies to liquified anhydrous ammonia, carbon dioxid and sulphur
dioxid, which are the substances most commonly used in commercial
refrigerating machines. These liquids are extremely volatile, their
change of state takes place very rapidly, and their latent heat is
absorbed at a corresponding rate. Their boiling point is sufficiently
low, under atmospheric or other conveniently produced pressure, to give
the temperature desired. Although the same principles underlie the use
of all such fluids, their physical properties vary, and consequently
demand different treatment in order to produce the best results.
“The theoretical requirements of a good refrigerant are: A low boiling
point at ordinary pressure, a large latent heat of vaporization, and
a small specific volume. A low boiling point is desirable, because
it makes operation possible with comparatively low pressure in all
parts of the system; therefore, the machines and accessories may be
of lighter construction, with smaller loss of gas by leakage. As the
latent heat of vaporization is, to a certain extent, a direct measure
of the cooling effect, it is obvious that the greater the heat of
vaporization the better the refrigerant. The specific volume of the
refrigerating agent determines the volume of the cylinders of the
compressor, consequently the size and weight of the machine.
“In comparing the three refrigerating agents which are considered
applicable to the dairying industry, viz., ammonia, carbon dioxid, and
sulphur dioxid, it will be noted by referring to tables giving the main
characteristics of the agents that, assuming the limits of operation
are between 5° F. and 85° F., the absolute pressures are: Ammonia from
27 to 175 pounds, carbon dioxid from 290 to 1,000 pounds, and sulphur
dioxid from 9 to 65 pounds. Taking the boiling points of the liquids at
the temperature at which the liquid boils under atmospheric pressure,
it will be noted that there is a wide difference in their boiling
points as well as their latent heats of vaporization. Ammonia boils
at 28.5° F. below zero and has a latent heat of vaporization of 572.8
B. T. U. Carbon dioxid boils at 110° F. below zero and has a latent
heat of vaporization of 140 B. T. U. at a pressure of 182 pounds per
square inch absolute. The latent heat at atmospheric pressure is not
definitely known. Sulphur dioxid boils at a temperature of 14° F. and
has a latent heat of vaporization of 162.2 B. T. U.
“For practical purposes the value of a refrigerant depends upon its
boiling point, its latent heat of vaporization, and upon the pressure
at which it can be used.
“To maintain a zero temperature with ammonia as the refrigerant an
absolute pressure of 30 pounds per square inch is required in the
evaporating coils; with carbon dioxid, 310 pounds absolute; and for
sulphur dioxid, 10 pounds.
“Ammonia has a much greater latent heat of vaporization and the working
pressures are not excessive, but it has the disadvantage that it
corrodes brass or any other copper alloy; consequently only iron or
steel can be used in the construction of those parts of the machine
with which the agent comes in contact. The pressures of carbon dioxid
are so high as to cause trouble in keeping the stuffing box and joints
tight. A relief valve is often placed in the high-pressure side of
the system in order to protect it from excessive high pressures. It
is noncorrosive, nonexplosive, and is not dangerous to life when
diluted with air. The high pressures necessary, combined with the
small specific volume of the gas, make it suitable for use with a very
compact machine. As the lower pressure of sulphur dioxid is below the
atmospheric, any leakage of air will be into the system and will cause
corrosion of the metal by forming sulphurous acid. The low pressures
required in using sulphur dioxid as a refrigerant in connection
with its large specific volume makes a large and cumbersome machine
necessary. The ratios of the volumes of the cylinders necessary for a
given capacity of machine, taking that of carbon dioxid as one, are
approximately as follows: Carbon dioxid 1, ammonia 4.4, sulphur dioxid
13.”
=97. Operation of refrigerating machines.=--The refrigerating material
commonly used in ice-cream plants is ammonia. There are two types of
ammonia machines, the compression and the absorption systems.
=98. The compression system.=--The following, Fig. 43, shows the
simplest compression system of refrigeration. The liquid ammonia in the
small container is allowed to evaporate but it really boils. In order
to boil or to change from a liquid to a gas, it must absorb heat. This
heat is taken from the surrounding material, in this case brine. This
cools the brine in the container in which the vessel of ammonia is
placed. In this case, there is no control of the rate of evaporation of
the ammonia.
[Illustration: FIG. 43.--Simplest compression system of refrigeration.]
An arrangement by which the evaporation or escape of gas can be
controlled is shown in Fig. 44. The flow of liquid is regulated by
an expansion valve and the liquid is carried into a brine tank or
refrigerating room and from the coil of pipe in there gas is allowed
to escape in the atmosphere. The change from a liquid to a gas in this
coil of pipe cools the surrounding substance, either brine or air. This
is the usual arrangement of the compression system; the remainder of
the system is to return the evaporated liquid or gas back to a liquid
in the ammonia tank.
=99. Parts of a compression system.=--The functions and principal parts
of a compression system of refrigeration are as follows:
_Compressor._--This is a specially designed valve pump. It takes the
gas from the evaporating coils, compresses it and forces it into the
condensing coils. This reduces its volume and produces heat.
[Illustration: FIG. 44.--Compression system of refrigeration in which
the flow of liquid is regulated by the expansion valve. The liquid
changes to a gas in the coil of pipe, thereby cooling the brine. The
gas finally passes off into the atmosphere.]
_Oil-traps._--In the compressor, there is danger of some oil becoming
mixed with the ammonia. The purpose of the trap is to separate the oil
from the ammonia. It is usually placed next the compressor.
_Condensing coils._--This consists of a double coil of pipe, one within
the other. Cold water is circulated in the inner pipe and the ammonia
in the space between the inner and outer pipe. In the condensor the
heat is taken up by the water and the ammonia again becomes a liquid.
_Ammonia receiver or storage tank._--From the condensing coils, the
liquid ammonia passes into a receiving or storage tank until wanted for
use again.
_Expansion valve._--It is by means of this valve that the evaporation
of the ammonia is regulated or, in other words, the rate of flow of the
ammonia from the receiving tank is regulated by this valve.
_Evaporating coils._--These coils are usually located in the material
to be cooled, ordinarily the air of the refrigerator or a brine tank.
In these coils, because of the reduced pressure, the ammonia liquid
evaporates or boils and in doing so takes up heat. This, as has been
explained before, causes the cooling. From the evaporating coils the
ammonia gas goes back to the condensor. This makes a complete circuit
for the ammonia.
=100. Operation of direct expansion compression system.=--The
following diagram, Fig. 45, shows the complete system of direct
expansion refrigerating. When the evaporation coils are placed in the
refrigerator and the heat is taken directly from the air, it is known
as the direct expansion system.
[Illustration: FIG. 45.--Complete system of direct expansion
refrigerating machine.]
The liquid ammonia passes from the ammonia receiver (R) through the
expansion valve (X) into the evaporating coils (E). Here the ammonia
changes from a liquid to a gas and in so doing takes up heat from
the refrigerator. The ammonia gas passes to the compressor (C). From
the expansion valve to the compressor is what is usually known as
the low pressure side because here the pressure is reduced in order
that the ammonia can boil or evaporate. For this reason the expansion
valve is sometimes called the reducing valve. The gas is compressed
in the compressor (C), then passes through the oil-trap (S) where
the oil is taken out and then through the condensing coils (W) where
the heat is absorbed and the gas changed to a liquid and back to the
ammonia receiver (R). From the compressor to the expansion valve is
what is known as the high side because of the pressure caused by the
compression.
=101. Location of evaporating coils.=--As explained above, the location
of the evaporating or expansion coils in the refrigerator so that the
heat is taken directly from the air is known as the direct expansion
method of refrigeration. In order to keep a refrigerator cold with this
method, it is necessary to run the compressor almost continuously.
In some cases the evaporating or expansion coils are placed in brine
tanks. The heat is then taken from the brine which in turn cools the
air. By the use of the brine tanks, the compressor may be stopped and
the cold brine will tend to maintain a more uniform temperature in the
refrigerator while the compressor is not running.
A combination of the direct expansion and brine storage tanks is shown
in Fig. 46. This is a common arrangement in refrigerators where a low
temperature is desired and it is not economical to run the compressor
continuously. The brine storage tanks are sometimes called congealing
tanks.
In some cases it is desirable to have refrigeration in some place where
it is not possible to use either the direct expansion or the brine
storage system; for example, to freeze ice-cream. In this case the
expansion coils are located in a brine tank and the cold brine pumped
to the place where refrigeration is desired. Such an arrangement is
shown in Fig. 47. The brine flows from the tank (T) in the refrigerator
to the pump (P). It is then pumped through the ice-cream freezer
(I) and back to the brine tank. The latter may be separate from the
refrigerator and contain cans of water for the making of artificial
ice. Most plants make artificial ice for packing the ice-cream for
delivery.
[Illustration: FIG. 46.--Combination of direct-expansion and brine
storage tanks. This is the same system as shown in Fig. 45 with the
brine tank T added in the refrigerator.]
=102. Notes on operating compression system.=--In order to operate
a refrigerating machine economically, certain factors must be given
constant attention. When ammonia is passing through the expansion
valve, it should be covered partially with frost or the part where
the pressure is reduced will be frosted as will the pipe leading
from it into the refrigerator. This cannot be prevented. The proper
adjustment of the expansion valve is very important. If too wide open,
the flow of liquid will be too rapid, it will not all vaporize in the
evaporating coils and so will take heat from the air after leaving the
refrigerator, causing the pipe from the refrigerator to the compressor
to become covered with frost. This is a waste and may cause a high
pressure on the low side.
[Illustration: FIG. 47.--Arrangement where it is desired to use cold
brine in some machine such as an ice-cream freezer. This is the same
refrigerating system as shown in Figs. 45 and 46.]
Usually the low pressure side carries 10-20 pounds pressure and the
high side 125-150 pounds.
If the ammonia passes the expansion valve too fast, as mentioned above,
it may cause the compressor to labor too hard and so cause pounding.
If not enough ammonia is passing the expansion valve, the rate of
refrigeration is reduced.
The cost of operating a refrigerating machine varies. The principal
items are: 1, Power; 2, water; 3, incidentals (refrigerant oil, and
the like); 4, repairs. No figures can be given for the cost of a ton
of refrigeration because of the variation in the price of each of the
items mentioned.
Some very compact refrigerating systems are on the market especially
adapted for making ice-cream in places where space is limited. The
principle of operation of these machines is the same as all other
expansion systems.
ABSORPTION SYSTEM
The absorption system is not as common as the compression. When used,
it seems to be very satisfactory.
=103. Operation of absorption refrigerating system.=--The following
principles of operation, and Fig. 48 of an absorption refrigerating
machine, are contributed by Henry Vogt Machine Company.
“The first step is pumping a strong charge of what is technically known
as aqua ammonia, or, in plain terms, a solution of water and anhydrous
ammonia, from the absorber into the bottom pipe of the rectifier. It
is then forced upward through the inner pipes or tubes and out from
the top through a pipe connected to the top of the exchanger where the
strong liquid passes down through the inner pipes or tubes and out at
the bottom through a pipe connecting with the ammonia generator.
“Within the generator the ammonia gas is driven off from the strong
solution by the heat in the steam coils, leaving a weak solution of
aqua ammonia in the lower part of the generator.
“The generated gas, under pressure passing out at the top of the
generator, enters the rectifier through the top connection and is
forced downward through the outer pipes. In transit through the
rectifier, the strong aqua absorbing some of the heat in the gas,
condenses whatever moisture is in it. The gas passes out of the bottom
of the rectifier into a separator where baffle plates separate the
moisture from the gas.
[Illustration: FIG. 48.--Diagram of the Vogt absorption refrigerating
machine, showing pipe connections and directions in which the liquids
and gases travel throughout the entire system.]
[Illustration: FIG. 49.--General arrangement of double pipe absorption
machine, showing the connections and the direction in which the liquids
and gases flow.]
1. H. P. gas; 2. Purge; 3. Water outlet; 4. Purge; 5. H. P. trap;
6. H. P. gas; 7. Purge; 8. Water; 9. To sewer; 10. Purge; 11. Purge
drum; 12. Equalizing main; 13. Purge; 14. Steam coils; 15. Trays;
16. Pump-out; 17. Drain; 18. Gauge board; 19. Oil trap; 20. Exhaust
steam; 21. Trap; 22. Weak aqua main; 23. Strong aqua main; 24. Boiler
steam; 25. Aqua ammonia pump; 26. Exhaust; 27. Drain; 28. Pump-out;
29. Pump-in; 30. Pump-out; 31. Gauge lines, 32. Equalizing main; 33.
S. A. Draw-off; 34. Charging connection; 35. Charging connection;
36. Drain; 37. Check; 38. L. P. Gas; 39. Ammonia liquid; 40. Weak
aqua; 41. Regulating valve; 42. Water outlet; 43. W. A. Draw-off; 44.
Check; 45. Liquid mains; 46. Accumulator W. A. Draw-off; 44. Check;
45. Liquid mains; 46. Accumulator; 47. Outlet; 48. Drip; 49. Fresh
water main; 50. Check; 51. Expansion valve.
[Illustration: FIG. 50.--General arrangement of atmospheric absorption
machine, showing the connections and the direction in which the liquids
and gases flow.]
1. Water main; 2. Purge; 3. Purge; 4. H. P. Trap; 5. H. P. Gas;
6. H. P. Gas; 7. Drip; 8. Check; 9. Strong aqua; 10. Drip; 11.
Pump-out; 12. Weak aqua; 13. Gauge; 14. Trays; 15. Steam coils; 16.
Gauge glass; 17. Boiler steam; 18. Exhaust steam; 19. Grease trap;
20. Drain; 21. Gauge board; 22. Liquid main; 23. Strong aqua main;
24. Weak aqua main; 25. Gauge; 26. Trap; 27. Aqua ammonia pump; 28.
Exhaust; 29. Drain; 30. From boiler; 31. Air chamber; 32. Pump-in;
33. Equalizing main; 34. Charging connection; 35. Pump-out and
blow-in; 36. Drain; 37. Charging connection; 38. Blow-in line; 39.
Gauge line; 40. Liquid main; 41. Accumulator; 42. Expansion valve;
43. Purge; 44. Purge drum; 45. Water main; 46. Equalizing main; 47.
Gas main; 48. Check; 49. W. A. main; 50. W. A. Draw-off; 51. Strong
Aqua tank; 52. Gauge glass; 53. S. A. Draw-off; 54. Check.
“The moisture is trapped back to the generator while the dry gas
continues to the condenser, where it enters at the top of the shell
or coils. Being brought into contact with the water cooled surface
of the condenser, the sensible as well as the latent heat of the
ammonia is extracted, and the gas quickly liquifies. This liquid
ammonia is conducted to the brine cooler or refrigerating coils where
it evaporates by absorbing the heat contained in the brine or air
surrounding the coils, thus performing the work of refrigeration. The
vapor or gas thus formed is piped to the bottom of the absorber.
“The weak aqua ammonia, in the meantime, passes from the bottom of the
generator to the bottom of the exchanger and flows upward through the
outer pipes for the purpose of exchanging the heat with the strong aqua
ammonia flowing downward through the inner pipes.
“From the top of the exchanger the weak aqua is conducted to the bottom
of the weak aqua cooler, flowing up through the outer pipes to be
further reduced in temperature by cooling water passing down through
the inner pipes. Finally it flows in the top of the absorber where the
ammonia vapor from the refrigerating coils, owing to its great affinity
for water, is rapidly absorbed by the weak aqua, forming again the
strong solution of aqua ammonia. The double cycle of circulation is
thus completed. The same operation is repeated indefinitely.”
=104. Arrangement of double pipe and atmospheric absorption
machines.=--There are several types of the absorption machines. The
general arrangement and the direction of the flow of gases and liquids
are shown in Figs. 49 and 50.
CHAPTER IX
_PREPARING THE MIX_
Mix is a term applied to the unfrozen ice-cream. It is sometimes called
“batch” or “batter.” The amount of mix prepared at one time may be
enough for one or several freezers or for a whole day’s freezing.
=105. Importance of preparing the mix.=--The preparing of the mix is
one of the most important phases of the ice-cream business, because
of the control of flavor, the effect on the body and texture, and
financial considerations.
If the flavors were always uniform, it would be a simple matter to
prepare the mix. This not being the case, it requires considerable
practice and skill to know exactly how to blend them. The mixer of
the different materials should know which must be rejected and which
used and in what flavors of ice-cream. The sour or acid flavor can be
determined easily in the milk products by means of the acid test. For
its use, see Chapter XIV. Besides this, many other undesirable flavors
are present in the materials. For example, it would be unwise to try to
mix acid fruits with cream already high in acid, since this probably
would cause a pronounced sour taste and might curdle the cream. Some
makers believe that the flavor added to the ice-cream will cover up any
bad flavors in the milk products, but this is not the case. If there
is any undesirable flavor in the materials it can be detected in the
ice-cream. Of course the person preparing the mix has the receipt
or formula but this is only a general guide; the final test is the
taste. Each mix should be tasted before it is frozen to make sure that
the flavor is correct. If not palatable in the mix, it will not be in
the ice-cream. In some cases, it is necessary to have the flavor more
pronounced in the mix than is desired in the finished product because
the flavor may freeze out or become less pronounced.
From the financial viewpoint, mixing is one of the most important parts
of the whole enterprise. Here the question of whether the business is
to be a success or failure is largely determined by the cost of the
materials. After the materials have been determined, it is necessary
to see that the exact amount is used in each mix. This means that each
mix must be standardized, both for fat and total solids. For method
of standardization, see Chapter XIV. An example may illustrate what a
small loss will amount to in dollars and cost a gallon. Suppose 1000
pounds of cream testing 20 per cent fat were desired and instead of
this it tested 20.5 per cent fat. This would use 5 pounds more fat
which at $1.00 a pound would equal $5.00; the wages for a good man.
This 1000 pounds of cream would make approximately 250 gallons of
ice-cream. The $5.00 additional cost for 20.5 per cent cream would
make the ice-cream cost 2 cents a gallon more. This shows that a small
divergence in cost a gallon may make a big total difference especially
noticeable if near the dividing line between profit and loss. Another
example indicates how carefully the mix may be standardized to reduce
cost. An ice-cream plant found that the mix could contain .21 per cent
of acidity without injury to the quality of the product. Each material
was tested for acidity (see Chapter XIV), and because there was an
abundant supply of buttermilk for which there was no market, the mix
was standardized to .21 per cent acidity by the use of buttermilk. This
reduced the cost by using a material for which there was no market.
The body and texture are largely determined by the materials employed,
although the freezing and subsequent handling has a decided influence
on the quality.
Too much study cannot be given to the question of the materials to
be used in the mix nor too much pains taken to see that each mix is
properly standardized.
=106. Usual procedure in preparing the mix.=--Much detail variation
in preparing the mix is possible and yet obtain accuracy and good
quality of ice-cream. The usual procedure is as follows: The milk
products are first put into the container in which the mixing is to be
done. In a large ice-cream plant some type of the mechanical mixer,
Figs. 20, 21, 22, 23, and 24, is used. A view of a mixing-room is
shown in Fig. 51. The mixers are just above the level of the floor,
making it easy to put materials into them. In this case, the mixers
are above the freezers so that the mix flows by gravity. Each material
should be weighed or measured accurately. After the materials are
mixed together, it is often desirable to test them to make sure that
the desired standardization has been obtained. The sugar is weighed
next into the mix. The amount will vary according to the flavor and
materials used. For example, with sweetened condensed milk, less sugar
will be required. Time should be allowed before freezing for the sugar
to dissolve. This can be hastened by stirring, which may be done by
a mechanical or hand agitator, depending on the size of the mix.
Whichever method is employed, care should be exercised not to stir the
mix enough to cause the fat to churn. This would cause lumps of fat or
butter in the ice-cream.
[Illustration: FIG. 51.--Mixing room in large ice-cream plant.]
The stabilizer is added next. In some cases, such as the prepared
ice-cream powders, it should be mixed with the dry sugar and added with
it. If gelatine or gum tragacanth is used, it should be applied slowly
and the mix agitated to prevent lumps forming. For method of preparing
gelatine, see Chapter IV. If color is desired, it should be put in
just before the flavor. This will prevent streaks in the ice-cream.
Lastly, the flavor should be added, care being taken to use the exact
amount. In the case of fruit ice-cream, the fruit may not be put in
until the mix is partly frozen. If acid fruits are stirred in the mix
before partly freezing, the cream might curdle. If the fruit is added
to the mix and then frozen in an upright freezer, there is danger of it
settling to the bottom.
If it is desired to emulsify or homogenize the whole mix, this should
be done before the flavoring materials are added. The flavoring might
be lost during the process and pieces of fruit would clog the machine.
When ready to freeze, the mix should be tasted to make sure that
everything has been added and that the mix has the proper flavor. Of
course little can be told about the body and texture of the resulting
product by tasting the mix. But the flavor is a good index of that of
the ice-cream.
=107. Temperature of the mix.=--As will be pointed out in connection
with over-run, the temperature of the mix when it enters the freezer
is very important. If too warm, the cream will churn before it will
beat up or whip. Most of the mechanical mixers possess some means of
controlling the temperature of the mix. But the operator should make
sure that the mix is at the desired temperature. It should never enter
the freezer above 60° F. and the nearer 40° F. the better.
CHAPTER X
_FREEZING PROCESS_
The principles of freezing are the same whether a large or small
freezer is employed. It is usually harder to control the process in a
small receptacle. In a large plant the freezers are arranged in a row
or battery, as shown in Fig. 52. One man operates six to eight, with a
helper to carry the ice-cream to the hardening-room.
=108. Purpose of freezing.=--Freezing is for the purpose of cooling the
mix and getting it in such condition that it is edible while frozen.
If frozen without agitation it would be icy and grainy. If the mix
is placed in the freezer too warm, it is liable to churn. Freezing
incorporates air into the ice-cream and so gives pore space. The
increase in volume due to freezing is known as “swell” or “over-run.”
=109. Rate of freezing.=--If the freezing is not properly done, the
result is a loss in both quality and quantity of ice-cream. The rate or
time required to freeze is affected by different factors, depending on
the type of machine used.
In the brine freezer, the rate is dependent on the following factors:
1. Temperature of brine; 2. rate of flow of brine; 3. temperature of
materials when put into freezer; 4. materials in mix; 5. speed of the
freezer.
[Illustration: FIG. 52.--Battery of freezers in a large ice-cream
plant.]
In the tub and can freezer the rate is dependent on the factors: 1.
Proportion of salt and ice; 2. amount of brine; 3. mixture of salt and
ice and brine; 4. speed of freezer; 5. temperature of materials when
put into freezer; 6. materials in mix.
Ice-cream should not be frozen too fast or too slowly nor for too long
or short a period. If the extremes occur, the quality and quantity are
affected.
Results of freezing too rapidly:
1. Cannot obtain swell.
2. Causes cream of poor quality.
1. Soggy or heavy--due to lack of air space.
2. Grainy in texture.
3. Does not hold well in storage.
Results of freezing too slowly:
1. Cream is liable to churn, causing chunks of butter in the
ice-cream.
2. Greasy ice-cream.
3. Cannot obtain swell.
4. Ice-cream usually lumpy.
Results of not freezing enough:
1. Ice-cream is watery.
2. Ice crystals separate while hardening.
3. Do not obtain proper swell.
4. Fat rises to surface of the ice-cream.
Results of freezing too much or too long:
1. Liable to churn cream.
2. Lose swell.
3. Ice-cream is liable to be greasy.
4. Ice-cream is soggy and heavy.
The rate of freezing can be regulated much easier in the brine than in
the tub and can freezer. In the former the condition of the ice-cream
can be seen without stopping the machine, and also the temperature
taken. On the other hand, with the tub and can freezer, the machine
must be stopped each time and the cover removed in order to see the
condition of the ice-cream or to take the temperature of it. With the
brine freezer the rate of flow of the brine can be regulated. The
temperature of the brine alone is not important, but the rate of flow
must be considered. In the tub and can freezer the proportion of ice
and salt can be regulated, but this is not very satisfactory. The
ratio of salt to ice regulates the rate of freezing. (See page 108.)
Usually one part salt to twelve to eighteen parts of ice is the correct
proportion. The finer the ice and salt, the more rapid the freezing.
The rate of freezing is also affected by the amount of sugar and solids
in the ice-cream. The effect of sugar on the temperature is shown in
Table V.
TABLE V
Effect of sugar on freezing
_Percentage of sugar_ _Temperature of freezing_
_in solution_ _Degrees F._
Skim-milk 31.03
5 per cent solution of sugar 30.40
10 per cent „ „ „ 29.70
14 per cent „ „ „ 28.60
25 per cent „ „ „ 27.07
The effect of a large percentage of sugar on the freezing is especially
noticeable in the case of sherbets and ices. These freeze much slower
than ice-cream.
=110. Proper method of freezing.=--The question might be asked as
to the proper way to freeze ice-cream. Because of the many factors
involved, the only direct answer is to state that the process should
result in a mellow body, smooth texture and medium swell. The colder
the mix when it enters the freezer, down to 40° F., the better the
control. It should take from twelve to twenty minutes to freeze. The
mix should be cooled quickly to 32° F., then the flow of brine partly
shut off and the cream allowed to whip. When the cream is nearly
whipped, the brine should be turned on gradually and the cream allowed
to freeze. When the mix is partly frozen, the fruit should be added,
soon enough so that there will be time for it to become uniformly
distributed in the mix. It is the usual practice to crush the whole
fruits before putting them in the freezer. This can easily be done
by forcing them through a food chopper. The cream should come from
the freezer at a temperature of 26° F.-28° F. The appearance of the
ice-cream and its temperature is a good index when frozen enough. It
should have its peculiar characteristic (dead) not shiny appearance.
When the thermometer is placed in the freezer and drawn out, the
ice-cream should adhere to it and the part remaining on the thermometer
should retain its identity for a few minutes.
Experiments[26] show that between 29° F. and 26° F., the volume of the
ice-cream increases as the cream whips. The flow of brine, therefore,
should be regulated so that the cream will be at the temperature at
which it will whip, for the maximum of time. If the freezer is run with
the mix too warm, the cream will churn, and if the mix is too cold, the
cream will not whip.
[26] Washburn, R. M., “Principles and practice of ice cream making,”
Vt. Exp. Sta., Bul. 155, 1910.
In a tub and can freezer it is difficult to control the factors
regulating the rate of freezing. When the mix begins to thicken and
so turns hard, the speed of the freezer is increased. This beats up
the ice-cream and causes more swell. When the dasher and ice-cream are
removed, the freezing-can will float in the brine, causing considerable
difficulty when the next mix is ready to be frozen, since it will not
easily go back in place. If the freezing-can cannot be centered in the
tub, the cold brine should not be wasted, but should be dipped out and
poured back after the can is in place. This saves considerable ice. In
many plants, no attempt is made to center the can in the brine, this
being dipped out as soon as the ice-cream is removed.
One of the important factors in freezing is to obtain the proper swell.
So far as this is concerned, the time to draw the ice-cream from the
freezer can be told by the over-run tester. (See Chapter XIV.)
=111. “Over-run” or “swell.”=--It should be the aim of the person
freezing the ice-cream to obtain the proper over-run with each freezer.
A large number of factors affect the amount of swell, and the possible
combinations of these must be known. If too much swell is obtained,
the ice-cream will be very porous, light and fluffy, and have a grainy
texture; if not swell enough, it will be very heavy and soggy and may
or may not be grainy in texture. For the best results, a medium swell
is to be desired. The factors affecting swell[27] may be divided into
two general classes: kind and preparation of materials used, manner or
method of freezing.
[27] Washburn, R. M., “Principles and practice of ice-cream-making,”
Vt. Exp. Sta., Bul. 155, 1910; Baer, A. C., “Ice-cream making,” Wis.
Exp. Sta., Bul. 262, 1916; Mortensen, M., “Factors which influence the
yield and consistency of ice-cream,” Ia. Exp. Sta., Bul. 180, 1918;
Ellenberger, H. B., “Swell in ice cream,” Thesis, Graduate School,
Cornell Univ., 1915.
I. Kind and preparation of materials used.
1. Age, viscosity, acidity, and fat-content of milk and cream.
2. Size of fat globules in cream.
3. Ageing of mix.
4. Pasteurizing of milk and cream.
5. Use of homogenizer.
6. Use of emulsor.
7. Methods of mixing.
8. Use of condensed mix.
9. Amount of sugar.
10. Different kinds of flavoring.
11. Fillers and binders.
12. Total solids in mix.
The older the milk and cream and the more acidity they contain, the
more viscous they will be. This is to be desired since it will whip
more readily. For test for viscosity, see Chapter XIV. The more fat
present in the milk and cream the more viscous they will be and the
smaller the fat globules, the more the cream and milk will whip. It
is commonly known that in order to obtain viscosity and swell, aged
cream must be secured. Instead of ageing the milk and cream, some
manufacturers age the whole mix. If only the former are aged and these
should sour, they could be churned into butter. However, if the sugar
and flavoring are added to the mix and the whole aged and in the
process become sour, the cream would not make good butter when churned.
Therefore, there is danger of greater loss when the whole mix is aged.
Pasteurization temporarily destroys the viscosity of the milk and cream
and as a result pasteurized cream must be aged longer to restore the
viscosity. The homogenizer and emulsor breaks the solids of the milk
and cream into smaller particles. In some plants the whole mix is
homogenized or emulsified before going to the freezer. This increases
the viscosity and because of this and of the smaller particles, more
swell is possible without sacrificing quality. With the emulsor, cream
can be made from butter and skim-milk, but it lacks the force of the
homogenizer, and so cannot break up the solids as can the latter.
Emulsified cream is more viscous than raw cream of the same age.
While mixing, care should be exercised not to churn the cream. If
churning takes place, it reduces the solids and so the possible swell.
By the use of condensed or powdered milk, the amount of total solids in
the mix is increased. Condensed milk usually causes the mix to become
more viscous. The amount of sugar is important only because of its
bulk; the more sugar added, the more solids in the ice-cream. The swell
is affected by the flavoring since some flavors add more bulk.
Authorities disagree as to the effect of binders and fillers on swell.
If some cause an increased swell, this is very slight. The total solids
in the mix have a decided influence on the amount of swell that can
be obtained without injury to the quality of the ice-cream; the more
solids in the mix, the more swell.
II. Manner or method of freezing.
1. Speed of dasher in freezer.
2. Temperature of mix entering the freezer.
3. Temperature of brine and rate of flow.
4. Temperature of mix while whipping.
5. Time of whipping.
6. Total time to freeze.
7. Temperature of ice-cream when drawn from freezer.
8. The amount of mix in the freezer.
The manufacturers of the different freezers have studied their machines
and determined the speed at which they should run. The ice-cream-maker
should see that the freezer runs at the speed indicated.
The nearer the temperature of the mix to 40° F. when put into the
freezer, the easier it is to obtain the swell.
Mortensen[28] says “that a temperature of about 6° F. for the
circulating brine would be the most desirable when using a 20 per cent
raw cream. For pasteurized cream a temperature of from 8 to 10° F.
gave the best results, while for emulsified cream about 10° F. and for
homogenized cream 14° F. proved the most satisfactory.” No record of
the rate of flow of brine is recorded. The temperature and flow of the
brine should be such that the desired swell is obtained together with
the quality.
[28] Mortensen, M., “Factors which influence the yield and consistency
of ice-cream,” Ia. Exp. Sta., Bul. 180, 1918.
Washburn[29] shows that the mix whips at certain temperatures, usually
from 32° F. to 29° F. The length of time of whipping has a decided
influence on the quality of the ice-cream and the amount of swell.
[29] Washburn, R. M., “The principles and practice of ice-cream-making,”
Vt. Exp. Sta., Bul. 155, 1910.
The total time to freeze has a noticeable effect on the quality of the
ice-cream and the amount of swell. If frozen too quickly, swell will
not be obtained and if too long, swell will be lost.
Washburn[30] proves that the temperature at which the ice-cream is
drawn from the freezer has a marked effect on the swell. If frozen too
cold, the swell is lost.
[30] Washburn, R. M., “The principles and practice of ice-cream-making,”
Vt. Exp. Sta., Bul. 155, 1910.
According to Mortensen[31] the amount of mix in the freezer influences
the swell. For the best results, the freezer should be about half full.
[31] Mortensen, M., “Factors which influence the yield and consistency
of ice-cream,” Ia. Exp. Sta., Bul. 180, 1918.
Certain combinations of the factors mentioned above will increase the
swell, while certain ones will decrease it.
To obtain swell:
1. Have viscous milk and cream.
2. Age the milk and cream or mix.
3. If pasteurized milk and cream are used, they should be aged until
viscous.
4. The cream and milk or whole mix should be homogenized or
emulsified.
5. Condensed milk in the mix would aid in obtaining swell.
6. The mix should contain at least 30 per cent of total solids.
7. The dasher should run at the required speed.
8. Mix should enter freezer as near 40° F. as possible.
9. There should be a supply of cold brine, from 6° F. to 10° F.
10. The cream should be whipped for a moderate time in the freezer.
11. The mix should fill the freezer half full.
12. It should require 12-20 minutes to freeze.
13. The ice-cream should not be below 27° F. when drawn from the
freezer.
The converse of these conditions will cause a decrease in the amount of
swell.
=112. Condition of ice-cream when removed from freezer.=--When taken
from the freezer, the ice-cream is in a semi-solid condition. It
is soft enough to flow from one container to another and yet hard
enough to retain the incorporated air. In order to use the freezer
over and over, the ice-cream is usually placed in pack-cans to harden.
A parchment paper is put over the top of the can before going to
hardening-room. The ice-cream can be drawn from brine freezers directly
into the pack-cans. With the tub and can ice freezers, it is necessary
to dip the ice-cream from the freezer into the pack-cans. This is more
easily done if the dasher is first removed.
=113. Freezing sherbets and ices.=--The foregoing statements apply
to ice-cream and may or may not be applicable to sherbets and ices.
Because of the higher percentage of sugar and water, the latter usually
freeze more slowly. Any difference in procedure is noted under the
receipt for sherbets and ices.
CHAPTER XI
_HARDENING ICE-CREAM_
Ice-cream which is of good quality up to this stage in the
manufacturing process may be spoiled or the quality impaired by
improper hardening. The object, as its name indicates, is to harden
the semi-frozen product after it is frozen in the freezer. During the
time that the ice-cream is hardening, the flavors of the different
ingredients blend to give the desired characteristic flavor.
=114. Methods of hardening.=--The ice-cream may be hardened in the
freezer, but this allows only one mix to be frozen and the machine
cannot be used again until the product is consumed. This method is
ordinarily followed with the small hand freezers. With the larger
freezers, however, the ice-cream is hardened in pack-cans (Fig. 25)
or bricks. (Fig. 58.) This allows the freezer to be used over and
over. The ice-cream can be drawn directly from the brine freezer into
the pack-cans or bricks; however, with the salt and ice freezer, the
ice-cream must be dipped by hand. Various ladles or scoops have been
devised for this purpose. (Fig. 53.) These are more or less rounded on
the edge to scrape the sides of the freezing-can.
The ice-cream in the pack-cans or bricks may be hardened in any one
of several ways: packing in an ice and salt mixture, setting in cold
brine, setting in a cold room called a hardening-room. The first two
are not advisable for a large ice-cream plant because of the work and
space required.
[Illustration: FIG. 53.--Different styles of transfer ladles or scoops.]
=115. Hardening in ice and salt mixture.=--When the ice-cream is
hardened in a salt and ice mixture, the cans are placed usually in a
large plank box, Fig. 54, so that there will be a space of four to
six inches between the cans and the box. The size of the box will be
determined by the amount of ice-cream manufactured. If five-gallon
cans are used, it is advisable to build the box in compartments which
will hold six. This will require a box 26 inches wide by 32 deep by 36
long, outside measurement, with a hinged cover for each compartment.
The box should be made of two-inch matched lumber so that it will not
leak. There should be a hole in the side near the bottom so the brine
can be drawn off. Before beginning to freeze, it is advisable partly
to pack the cans in the box. A layer of four to six inches of cracked
ice should be placed in the bottom of the box, then the cans placed
in position and the box filled about two-thirds the height of the can
with cracked ice. Some salt should be sprinkled on the ice and the box
filled to the top of the cans with cracked ice. This cools the cans
so that there will be no melting when the ice-cream is put in. The
ice-cream may be poured directly from the freezer into the pack-cans
or first it may be put into some container which is easier to handle
and then poured from it into the pack-can. When all the cans in the
compartment are full, they should be covered to a depth of four to
six inches with ice and salt. These may be mixed before putting in the
box or they may be placed in alternate layers. The proportion of salt
to ice for hardening is about one part of salt to eighteen or twenty
parts of ice by weight. Most of the salt should be placed in the upper
third of the ice, because as the ice melts the salt goes into solution
and so is carried to the bottom of the box where it comes into contact
with ice where there is little or no salt. For packing, a coarse
salt is to be preferred as it dissolves more slowly. After standing
overnight in the pack-cans, the ice-cream should be hard. It may be
shipped out or held until wanted. If shipped the cans may be packed in
tubs, observing the same precaution of placing the salt in the upper
third of ice. Instead of packing in a tub, the cans may be put in a box
or cabinet on the delivery wagon. If the ice-cream is to be held in
the hardening-box, it should be repacked twice a day. This is done by
jamming down the ice and salt. The cans should then be recovered with
ice and salt. The brine which forms should be allowed to escape from
time to time so that it will not run into the cans or cause them to
float. The following figures on the amount of ice and salt used were
obtained by the “Ice-Cream Trade Journal.”[32] They are the average of
a number of plants:
[32] “Ice-Cream Trade Journal,” Vol. V, No. 6.
Average output of ice-cream per day, summer 395 gallons
Average output of ice-cream per day, winter 43 „
Amount of ice used per 100 gallons of ice-cream 1928 pounds
for freezing 614 „
for hardening and storage 914 „
for shipping delivery or cabinets 400 „
Amount of salt used per 100 gallons of ice-cream 190 „
for freezing 73 „
for hardening and storage 82 „
for shipping delivery or cabinets 35 „
[Illustration: FIG. 54.--Plank box for hardening ice-cream in a salt
and ice mixture. The cans are placed in perforated cylinders so that
they may be changed and the ice will not fall in and fill the space.]
=116. The slush-box or brine-box method of hardening.=--In this method,
the pack-cans instead of being packed in ice and salt are placed in
a box or tank of brine. This brine is usually cooled by means of a
mechanical refrigerating system, and circulated with a pump. Great care
must be exercised or the brine will get into the ice-cream.
=117. The hardening-room.=--In the large ice-cream plants, a cold room
is maintained in which the pack-cans are set to harden. This room is
cooled by mechanical refrigeration and the temperature should be very
near 0° F. or below. There are three general types of hardening-rooms,
depending on the location of the evaporating coils and the air
circulation.
=118. The still-air type.=--This type of hardening-room is used in the
smaller ice-cream plants. The evaporating coils are placed directly in
the hardening-room and usually arranged in such a way that shelves are
formed with parts of the coils on which the cans of ice-cream are put
to harden. (Fig. 55).
=119. The gravity-air type.=--In this system the coils are placed in a
bunker-room directly over the hardening-room and designed so the air
will circulate in a natural manner.
[Illustration: FIG. 55.--Still-air hardening-room showing evaporating
coils forming shelves on which the pack-cans of ice-cream are placed to
harden. Other evaporating coils may be seen on the sides and ceiling.]
=120. The forced-air type.=--This system locates the coils in a
bunker-room usually, directly over the hardening-room, and the air
is forced to circulate by means of a fan or blower. (Fig. 56). The
forced-air system is considered the most efficient. The effect is
the same as the temperature of the air on the body. With the same
temperature, the cold is more noticeable and more penetrating on a
windy day than when the air is still. The same is true in the hardening
of the ice-cream. The objection to the still-air hardening-room is the
longer time required to harden the product. The objection to the
forced-air room is the danger of losing too much refrigeration when the
doors are opened unless the fan causing the air circulation is stopped
before opening.
=121. Defrosting the coils.=[33]--“One of the most troublesome things
to be contended with in ice-cream hardening-rooms, cooled by means of
refrigerating machines, is the accumulation of frost or snow on the
coils, and up to the present time no thoroughly satisfactory method has
been devised which will meet with success under all conditions, taking
into consideration, method of operation, design of coils, and the like.
[33] Carpenter, M. R., “Defrosting of coils in hardening-rooms.”
“Ice-Cream Trade Journal,” Vol. XI, No. 4.
“The most serious objection to this accumulation is the loss in
efficiency, which may amount to as much as 50 or 75 per cent, depending
on the thickness of the coating and the interference with the air
circulation. The other objections are of minor importance and need not
be considered here.”
1. _Cooper system._
The Cooper system consists of a trough perforated at the bottom and
placed directly over each stack of coils, and in which are put lumps of
chloride of calcium. This substance, on coming in contact with moisture
in the air, will dissolve slowly and drip down over the coils, thereby
keeping them practically free of frost at all times. It may be asserted
that this is not a defrosting device; however, prevention is better
than cure.
This system can be applied to the first and second types of rooms,
as in these cases the floor under the coils is made water-tight and
arranged to catch the drip from the coils. It is not suitable for
use in the third type, however, as the drippings would fall upon the
cream-cans and on the floor of the room. It is possible to catch these
drippings and by boiling or evaporation recover the calcium, which can
be used over again or in strengthening the brine in the tanks.
[Illustration: FIG. 56.--Forced-air hardening-room.]
The objection to this system is the labor involved in placing it in the
troughs, for usually the coils are close together and are in a room
with little space around and over them for a man to work; also, the
rooms being cold, it is a very uncomfortable task. It may be possible,
in designing rooms, to provide space in which to work, or to fill the
cans outside the room and then place in position.
2. _Cold brine drip system._
This system consists of a means of spraying cold brine (calcium or
salt) over the coils. Over each stack of coils is placed a trough,
slotted or perforated pipe, similar to the water pipe or trough on
atmospheric condensers. Brine from the main tank or circulating system
is turned into the trough and allowed to drip over the coils either
continuously or intermittently as may be required.
In this system the brine must be very strong or it will freeze on the
lower coils, especially if the frost is allowed to accumulate to any
extent before defrosting, or unless the coils are out of commission
entirely during the operation. This brine is sometimes allowed to drain
directly back into the brine tank, although this is poor policy as it
weakens the brine and has a tendency to make it (in the case of calcium
brine) acid, owing to its contact with the air. A better way, if it is
possible to do so, is to drain it back into a tank, where it can be
boiled and thus brought to its proper strength before returning to the
main tank. This system has the advantage of being operated with little
labor and under comfortable conditions, providing the controlling
valves are placed outside the room and of easy access. In case the
frost is allowed to accumulate to any extent, this system will not work
as quickly as may be desired. One great advantage, however, is that it
will not warm up the hardening-room, and if operated often and properly
it will keep the coils free of frost and not require the room to be
out of commission. This system is suitable for use in first and second
types of rooms.
3. _Hot brine system._
This is arranged the same way as the cold brine drip system as far as
interior arrangement on coils is concerned, but instead of using brine
from the main tank, a special tank with steam coil is provided and
the brine is pumped into the trough in a hot condition and allowed to
drain directly back into the tank. This system is quick in its results.
A heavy deposit of frost can be removed in this way and it is easily
operated.
The principal objection is the great amount of moisture it will cause
to be deposited on the walls and ceiling of the room. It also requires
the room to be out of commission a short time while being operated.
However, it does not seem to have much effect on the temperature after
it is shut off.
This method can also be made a cold brine system by boiling off after
using, then letting it stand until it is cold before utilizing again.
However, it will still deposit some moisture and it has been found best
to keep the room out of commission while operating. Another tank with
refrigerating coil placed so as to cool this brine before using might
be beneficial, although in this case it resolves itself into system No.
1. This can be applied to first and second types.
4. _Air blast system._
In this system the air is so designed that the bunker-room can be
shut off from the hardening-room and openings arranged so that the
circulation fan can draw warm air from outside, blow it across the
coils and discharge it at the opposite end. This is a very satisfactory
and quick method, although it leaves some moisture deposited on the
walls of the room and has a tendency to warm things up a little. This
system, of course, needs a fan and is suitable for the first type only.
5. _Hot gas system._
This is a radical change from those systems considered, as it works
from the inside out. The success of this system depends on the design
of the coils, headers and connections. The coils are arranged in such a
way that they are, by opening and closing a few valves, converted into
an ammonia condenser with the hot ammonia gas from the discharge of the
compressor entering the top pipe of coils, and, as it is liquefied,
running by gravity back to the ammonia receiver. In operating, it is
necessary to have the room out of commission unless the coils can be
arranged in independent batteries.
This system can be applied to any type of room provided the coils are
properly designed and the receiver on a level below the lowest coil.
Also, there must be enough additional refrigeration to enable the
compressor to continue in operation in order to supply the hot gas.
6. _Warm liquid system_.
The coils, headers and piping are so arranged that the liquid ammonia
on its way to other rooms can be passed through coils which are to be
defrosted. It is self-evident that it is necessary to maintain the same
pressure on these coils as obtains in the main liquid line, also that
a considerable amount of ammonia must be expanding at other points in
order to keep a quantity of liquid flowing through the coils.
When conditions are right, this system is very satisfactory, as it can
be operated with a minimum of labor and has the advantage of conserving
all the energy previously expended in freezing the ice on the coils. In
applying, special consideration must be given to the method by which
the ammonia is fed into the coils. It is more easily applied to the
flooded system, as in this case it is only necessary when defrosting
is completed to cut off the flow of hot liquid, open the suction line
from coils and allow the liquid remaining in the coils to expand or
evaporate to accumulator, without danger of flooding over into the
compressor. After this liquid is partly evaporated, the valve on the
feed line from accumulator is opened, and the coils are again in full
operating condition.
In applying this system to direct expansion coils, care must be
exercised to provide means either to drain the liquid back into the
ammonia receiver before opening the outlet from coils into the main
suction line, or to expand this liquid through other coils; otherwise,
the liquid is liable to reach the compressor with disastrous results.
The application of this system should be attempted only by those
thoroughly competent to consider all phases of the situation and if
properly applied is one of the most efficient and satisfactory methods
of defrosting yet devised. It can be applied to practically any type of
room providing, as stated, the other conditions are suitable.
It has been the writer’s experience that the coils in forced-air
circulating types give the most trouble, due to the heavy frost, partly
from the very rapid accumulation and partly for the reason that these
coils being out of sight are more likely to be neglected, and after the
ice has become very heavy it is exceedingly difficult to get it all
off, without keeping the room out of use for a long time.
The gravity system also gives some trouble, but is not affected quite
so quickly as the forced-air type, owing partly to the design of the
coils which necessitates greater space between pipes. The still-air
type causes very little difficulty and some of these have been run
a whole season without being defrosted and without having their
efficiency materially reduced.
A large percentage of hardening-rooms have no arrangements for
defrosting and as a result it is often necessary to shut down and
remove the ice. All kinds of methods are used, such as scraping by
hand, spraying with water by means of a hose, placing salamanders in
the room or simply leaving the doors open and allowing the temperature
of the room to rise to such a point that the frost will melt.
=122. Time required for hardening.=--The time necessary for hardening
varies, but usually twelve hours is sufficient. The time depends on
the rate of removal of heat or the amount of cold supplied and the
insulation. The refrigerating boxes should be well insulated. This
is especially necessary because of the great difference between
the temperature of the hardening-room and that of the surrounding
atmosphere. Undoubtedly cork makes the best insulation. The thickness
varies, but it should be at least six or eight inches thick. Cork
should be kept dry or it is not a good insulator. When the ice-cream
becomes hard, it should be held at a low enough temperature so that it
will not soften or melt. After hardening, if the ice-cream melts or
softens it is liable to cause the separation of the ice crystals and
so result in a grainy textured product. If it becomes soft, the fat is
likely to rise unless the cream has been homogenized. Ice-cream should
not be held in the hardening-room for more than seven days.
When an ice and salt mixture is employed to harden the ice-cream, the
rate of hardening is determined by the amount of salt used. The coarse,
slow dissolving salt is to be preferred for hardening.
=123. Effect of hardening on quality.=--The two qualities of ice-cream
affected by hardening are the flavor and body and texture. While
hardening, the flavors of the different materials used blend to give
the desired characteristic flavor. Some flavors, especially vanilla,
will freeze out while hardening. The body and texture are affected
only through neglect. If the pack-cans are allowed to stand after they
are filled, before being placed in the hardening-room, some of the
ice-cream next to the sides and bottom will melt, causing a grainy or
icy texture. The same may occur if there is water in the bottom of the
pack-cans when the ice-cream is put in.
[Illustration: FIG. 57.--Brick ice-cream trowels. Straight and bent
handles.]
[Illustration: FIG. 58.--Quart and sectional brick molds. The sectional
bricks hold several quarts.]
=124. Fancy molded ice-cream.=--There are two kinds of fancy molded
ice-cream, bricks and molds to represent various objects. The ice-cream
is the same with the exception of the form in which it is hardened.
Sometimes a little more stabilizer is used to make the cream more firm.
The brick offers many possible combinations. Each kind of ice-cream
is put into the brick in a layer. Each layer is leveled with a brick
trowel. This trowel is square on the end and just the width of the
brick. (Fig. 57.) A different flavor and color of ice-cream forms each
layer. In some cases the center is a sherbet or pudding. Mortensen
suggests a center layer of solid frozen fruit and calls such ice-cream
Aufait. The size of the brick varies from a pint to several quarts.
(Fig. 58.) It is the customary practice to use sectional bricks (Fig.
58) which are the exact size to hold six to eight quart bricks. These
may have a single or double lid. When hard, the ice-cream is taken
from the sectional brick and cut into either quart or pint sizes.
In a large factory, a special hardening-room is employed for brick
ice-cream, which is kept as near 0° F. as possible. (Fig. 59.) The
contents are taken from the brick mold by applying cold water until
sufficient frost has been drawn from the mold to allow the ice-cream to
slide out. When a large number is made, a special brick-cutting machine
may be used. This will cut the bricks much faster and more uniform in
size than by hand. Sometimes if a knife is run around the sides of the
brick it will help loosen the ice-cream. Care should be taken not to
melt the ice-cream too much. In some instances the bricks are packed in
square, instead of round pack-cans for delivery. In this case a large
number of bricks would be delivered to the same place. The bricks are
wrapped in parchment paper, put into paper cartons and packed in ice
and salt for delivery.
[Illustration: FIG. 59.--Brick hardening-room.]
By means of a specially devised mold or brick known as a center mold
(Fig. 60), any letter, figure or form of object may be made in the
center of the ice-cream. To accomplish this, two different colored
ice-creams must be used. The form is produced by having one cover of
the mold with a tube of the desired shape to form the center figure.
The space around the tube is filled with one colored ice-cream and the
tube or center with the color desired in the center. When the brick is
sliced, this design is in the center of each piece of ice-cream.
[Illustration: FIG. 60.--Center mold and examples.]
[Illustration: FIG. 61.--Individual ice-cream molds and ice cave for
packing molds.]
By means of special molds, ice-cream may be hardened to represent
almost any object. (Fig. 61.) These molds are hinged pewter metal. They
vary in size from one or two quarts to an individual service. These
cannot be packed in an ordinary pack-can without jamming. They usually
are wrapped separately with waxed paper and hardened and delivered
in an ice cave (Fig. 61), which consists either of a round or square
pack-can into which a frame with shelves fits. The molds of ice-cream
are placed on these shelves.
CHAPTER XII
_JUDGING AND DEFECTS OF ICE-CREAM_
The judging of ice-cream is the comparing of one product with another
or of the one in question with the ideal. In order to make this
comparison more simple, a score-card has been devised. This gives a
numerical value to each of the characteristics of the material to be
judged and makes comparisons easy. The judge should be familiar with
the various qualities and defects of the material under his inspection.
=125. Score-cards.=--Several score-cards[34] have been suggested for
ice-cream, but no one is in universal use as is the case with both
butter and cheese.
[34] Baer, A. C., “Ice-cream-making,” Wis. Exp. Sta., Bul. 262, 1916;
Mortensen, M., “Classification of ice-creams and related frozen
products,” Ia. Exp. Sta., Bul. 123, 1911; Washburn, R. M., “Principles
and practice of ice-cream-making,” Vt. Exp. Sta., Bul. 155, 1910;
Frandsen, J. H., and Markham, E. A., “The manufacture of ice-cream and
ices,” Orange Judd Company, 1915.
In the New York State College of Agriculture at Cornell University, two
score-cards are used. They are as follows:
_Score-card No. 1_ _Score-card No. 2_
Flavor 45 Flavor 40
Body and texture 35 Body and texture 25
Richness 10 Bacterial count 15
Appearance 5 Richness 10
Package 5 Appearance 5
Package 5
------------------------- ------------------------
Total 100 Total 100
These score-cards consider the same characteristics except that No.
2 includes the bacterial count. Naturally the inclusion of another
characteristic changes the numerical value of the others. Score-card
No. 1 is for use only when there is not time to make a bacterial count,
such as for laboratory work. When an exact comparison is desired,
the bacterial count should be made. If undesirable or large numbers
of organisms are present, they affect usually the flavor and body
and texture, although this is not always true. For this reason, the
numerical value given to bacterial count has been taken from flavor and
body and texture.
=126. Explanation of characteristics mentioned in score-card.=--If the
ice-cream is to receive a perfect score, the characteristics should be
as defined. If not, the ice-cream is defective and the score should be
cut.
_Flavor._--The ice-cream should have a pronounced flavor which will
blend with that of the cream to give a clean, desirable typical flavor.
_Body and texture._--The body should be firm and mellow. It should
not be tough or rubbery, neither soft or mushy. The texture should be
smooth and velvety and entirely free from graininess and lumpiness.
_Richness._--If the ice-cream meets the legal requirements, it should
be given a perfect score. If it falls below, it should be scored zero.
_Appearance._--The ice-cream should have an attractive appearance and
be of the characteristic uniform color.
_Package._--The package should be neat and clean and, if for long
shipment, some provision should be made to protect the ice on top of
the packing-tub.
_Bacterial count._--An ice-cream which has a count of 20,000 should be
considered perfect. For each increase of 20,000 above this, one point
should be deducted from the score.
If a number of samples is to be scored, it is the usual custom to
examine several to gain an idea of how the quality runs. This is called
establishing a key or standard. When this has been done, all the
samples can be scored and the best will not be rated too high nor the
poorest too low.
=127. Defects in ice-cream.=--It is almost impossible to make an
ice-cream which does not have some defect. These can be discussed best
under the characteristics as given in the score-card.
=128. Defects in flavor= of ice-cream are largely due to objectionable
flavors in the materials employed, or to the use of too much or too
little of certain ingredients.
Some of the common causes are:
1. Use of cream of bad flavor.
2. Use of cheap flavoring extracts.
3. Use of too little or too much sugar.
4. Use of materials which do not give the characteristic flavor.
5. Disagreeable flavor due to use of poor fruits.
6. Lack of flavor due to use of too small an amount of flavoring
materials.
7. Too pronounced a flavor or not pronounced enough.
8. Condensed milk flavor.
9. Salty ice-cream.
10. Gelatine or gum tragacanth flavor.
Of the ten causes mentioned all but number one are within the control
of the ice-cream manufacturer. However, the flavor of the cream is a
very vital question and the one usually causing the greatest difficulty.
=129. Defects in body and texture.=--The texture refers to the
molecular structure. As the ice-cream is an emulsion of materials
of varying specific gravities, it is difficult always to get these
different ingredients to mix in the same manner. The greatest defect in
the texture of the ice-cream is graininess. This may be caused by the
incorporation of too much air or the separation of the water crystals.
After the ice-cream has been transferred from the freezer to the
pack-cans, the latter should be placed at once in cold surroundings;
if not, the cream around the outside and bottom of the can will melt
and on being hardened will be grainy, due to the melting and separation
of the water crystals. Graininess may be due to a lack of binder or
sometimes to the crystallization of the sugar in the condensed milk.
The body of the ice-cream refers to the structure as a whole. The
common defects in body are hard, brittle, soft or watery. In order to
obtain an ideal body, the ice-cream must contain a certain amount of
milk-fat and other solids; also this cream must be frozen properly.
If the ice-cream lacks solids, the body is very likely to be soft or
watery. The age of the cream, whether or not it has been pasteurized,
and method of freezing, have a decided effect on the body.
Sometimes in freezing the fat becomes churned; this results in chunks
of fat in the ice-cream. It is caused by the freezer running too fast
or by putting the cream into the freezer too warm.
The following summary of two bulletins gives the effect of solids on
the smoothness and keeping qualities of ice-cream and the effect of
binders on the melting and hardness. These directly affect the body and
texture.
Effect of solids on smoothness and keeping quality of ice-cream:[35]
[35] Brainard, W. K., “Smoothness and keeping qualities in ice-cream as
affected by solids,” Va. Exp. Sta., Tech. Bul. 7, 1915.
“1. Smoothness and keeping quality or stability of texture of ice-cream
are closely associated.
“2. Smoothness depends upon the amount and fineness of division of
solids present other than those in true solution, within limits, that
is, the smoothness depends upon the size and distribution of ice
crystals which in turn depend upon the number and nearness together of
minute solid particles which interfere with crystallization and reduce
the size of the ice crystal.
“3. Colloidal solutions of solids other than fat are best adapted to
ice-cream-making. The finer the division the better.
“4. The finer the emulsion of the fats the better the homogenizer has
its application in this respect.
“5. The keeping qualities of ice cream depend upon the stability of
the mix. That is, the keeping qualities of ice cream made from a given
mixture will depend upon the disposition of the solids in that mixture
to separate from the liquid, which in turn depends upon the fineness
of division of the solids. The finer the division, the better the
keeping qualities up to the point at which the solid merges into a true
solution.”
Effect of binders on the melting and hardness of ice-cream:[36]
[36] Holdaway, C. W., and R. R. Reynolds, “Effect of binders upon the
melting and hardness of ice-cream,” Va. Exp. Sta., Bul. 211, 1916.
“_Plain ice-cream._--In plain ice-cream (control) as the per cent of
fat increases the cream becomes softer. A medium amount of butter fat,
combined with other material than milk solids, produces a stiff cream.
When too much fat is present whipping takes place, producing a cream
that is soft and fluffy in appearance. Ice-cream made from eight per
cent cream is no harder than from nineteen per cent cream, while thirty
per cent plain cream is much softer than eight per cent or nineteen
per cent cream. In plain ice-cream the presence of fat increases the
power to resist melting. This resistance is most noticeable between the
melting of the eight per cent and nineteen per cent cream. Thirty per
cent cream shows the power to resist melting to a less degree.
“_Cream containing gelatine._--Gelatine in a large or small quantity
produces similar effects, depending upon the richness of the cream
used. The power to withstand pressure and the melting resistance
increases as the amount of gelatine increases, when compared with the
control ice-cream with a similar fat content. The hardest and most heat
resisting ice-cream is produced with a medium per cent of fat and a
large amount of gelatine. With gelatine, the presence of fat seems to
be essential to produce hardness and melting resistance until a point
is reached where whipping affects the texture. After whipping begins
the incorporated air reduces the hardness and melting resistance.
Ice-cream containing one ounce of gelatine per gallon has more the
appearance of pudding than ice-cream. Four ounces of gelatine gives
about the same hardness as four ounces of cornstarch, but it is much
better, producing a smoother cream which is more stable under ordinary
conditions.
“_Cream containing gum tragacanth._--Gum tragacanth with a low per cent
of fat produces an ice-cream that is slightly harder, with slightly
more power to resist heat than plain ice-cream. As the per cent of fat
is increased with this filler, the power to resist pressure and heat
decreases, falling below plain cream, showing that gum tragacanth acts
as a filler and not as a binder. Its most noticeable effects are on
the texture of the ice-cream, because of the nature of the gum, is to
impart a smoothness which becomes sliminess when large quantities are
used.
“_Cream containing cornstarch._--When cornstarch is used as a filler a
slight increase in hardness and melting resistance is noticeable with
nineteen per cent when compared with eight per cent ice-cream. Also
it produces an ice-cream that has more resistance to heat than plain
ice-cream of the same per cent fat. When used as a filler it compares
favorably with a similar amount of gelatine but the starch ice-cream is
more granular than the gelatine, while gum tragacanth produces a smooth
soft cream.”
=130. Defects in richness.=--The only defect in richness is a lack of
fat and solids not fat. The ice-cream should meet the legal standards;
if not it is defective.
=131. Defects in appearance.=--Many times the ice-cream does not have
an attractive appearance. It may be rough, grainy and coarse, or partly
melted. Often it will melt on the outside and run while the inside
will be very hard. The ideal ice-cream is one which will have the same
degree of softness throughout. The color is not always characteristic
as the fruit may not be distributed uniformly.
=132. Defects in package.=--Anything which detracts from the neatness
of the package is a defect. Badly dented or rusted cans are not
attractive. The tubs may not be clean or neatly painted or lettered.
The parchment paper circles being omitted from the top of the can
constitutes a defect.
CHAPTER XIII
_BACTERIA IN RELATION TO ICE-CREAM_
Much might be written regarding the factors affecting the growth of
bacteria, the preparation of the media, the incubating temperature,
the counting; this is all discussed in the various text-books on
bacteriology. Here only the relation of bacteria to ice-cream will be
considered.
It is commonly recognized that ice-cream contains large numbers of
bacteria. The table No. VI[37] on page 171 shows the average bacterial
count of ice-cream and the highest and lowest counts in various cities
and at different times in the same city.
[37] Hammar, B. W., “Bacteria and ice cream,” Ia. Exp. Sta., Bul. 134,
1912.
This table indicates that ice-cream made in different sections of
the United States has some extremely high counts and the average is
comparatively high when one considers the count of milk and cream
produced under clean conditions. The redeeming feature is that
ice-cream can be produced with low bacterial count. This shows the need
of a bacterial as well as chemical standard.
=133. Sources of bacteria in ice-cream.=--There are two sources of
bacteria in ice-cream, the materials employed and the utensils which
come in contact with the ice-cream. The latter source is entirely
under the control of the manufacturer. If materials used have a low
bacterial count, there is no reason why the ice-cream should not be low
in bacteria. If this is the case and the ice-cream has a high count, it
would indicate that the maker was careless and the utensils dirty.
TABLE VI
Summary of Bacterial Investigations of Ice-cream
_Average
_No. bacterial
_Source of _Date of samples_ count
ice-cream_ investigation_ examined_ per c. c._
Philadelphia 1905-06 49 17,833,031
Boston 1906-07 35 23,000,000
Washington 1906-07 263 26,612,371
Chicago 1909 89 16,662,134
Chicago 1910 386 15,401,000
Chicago 1911 1,800,000
Milwaukee 26
Des Moines 1911 10 19,920,000
I. S. C. Cream 1911-12 12 19,775,000
_Source of _Highest _Lowest
ice-cream_ count_ count_
Philadelphia 79,000,000 70,000
Boston 150,000,000 1,000,000
Washington 365,000,000 137,500
Chicago 125,000,000 20,000
Chicago 100,000,000 20,000
Chicago 200,000,000 90,000
Milwaukee 8,000,000,000 200,000
Des Moines 39,000,000 4,200,000
I. S. C. Cream 72,000,000 500,000
Ellenberger[38] found the minimum and maximum number of bacteria in the
materials used in the mix as given in Table VII:
[38] Ellenberger, H. B., “A study of the bacterial growth in
ice-cream,” Thesis, Cornell Univ., 1917.
TABLE VII
The Minimum and Maximum Bacterial Content of the Ingredients used in
the Mix
_Minimum_ _Maximum_
Standard cream per c. c. 1,150 37,600,000
Condensed milk per c. c. 31,500 59,800,000
Sugar per gram 20 255
Gelatine 48 891
Flavoring vanilla 10 321
The important fact brought out by the above table is that the milk
products are the source of most of the bacteria in the ice-cream. This
emphasizes the need of dairy products manufactured and marketed under
the most cleanly conditions. The ice-cream-maker in most cases has
little control over these factors. For the production and handling of
milk, see Chapter II. The numbers of bacteria may be reduced materially
by pasteurization.[39] This destroys the viscosity so that milk or
cream that has been aged and then pasteurized must be aged again to
regain it. There is great danger while ageing either pasteurized or raw
cream of a material increase in the numbers of bacteria. Great pains
must be taken to cool and hold or age it at a low enough temperature
so that the organisms will not develop. If this is not done, the result
would be practically the same as if it had not been pasteurized, so far
as numbers of organisms are concerned.
[39] Ellenberger, H. B., “A study of the bacterial growth in
ice-cream,” Thesis, Cornell Univ., 1917; Hammar, B. W., “Bacteria and
ice-cream,” Ia. Exp. Sta., Bul. 134, 1912; Hammar, B. W., and Goss, E.
F., “Bacteria and ice-cream,” Part II, Ia. Exp. Sta., Bul. 174, 1917.
Hammar gives the count of different samples of gelatine as follows:
TABLE VIII
Bacterial Count of Samples of Gelatine
_Bacteria in 1 c. c._
_Bacteria per_ _of ice-cream due_
_Sample No._ _gram_ _to gelatine_
1 113,000,000 565,000
2 14,000,000 70,000
3 35 0.2
4 4,200 21
5 85,000 425
This table shows the need of testing to make sure that the supply of
gelatine is low in number of bacteria. Usually in the better or more
expensive grades, the bacterial content is lower, but this is not
necessarily true. The method of preparation has much influence on the
bacterial content of ice-cream. (See Chapter IV.)
Sugar contains very few organisms. The greatest danger is that dirt may
get into the sugar due either to exposure or sifting through the cloth
sacks.
The flavoring materials may have a decided influence on the bacterial
content of the ice-cream. Vanilla contains very few organisms, but such
flavors as fruits may have large numbers of bacteria, especially if
they are not sound.
Hammar[40] reaches the following conclusions regarding the bacterial
content of the materials used in the manufacture of the ice-cream:
[40] Hammar, B. W., “Bacteria and ice-cream,” Ia. Exp. Sta., Bul. 134,
1912.
1. The cream unless pasteurized is the greatest source of the bacteria
in ice-cream.
2. After pasteurization cream can be stored at 0° C. for several days
with no important increase in the number of bacteria developing at 37°
C. on agar.
3. The bacterial content of gelatine is very valuable and some probably
add large numbers of bacteria to ice-cream in which they are used.
4. The vanilla extract plays a very small part in detaining the
bacterial content of ice-cream.
5. The sugar is comparatively unimportant as regards the number of
bacteria in the ice-cream made with it, if it has been properly
protected from dirt.
All the utensils, unless clean, may be a source of contamination to the
ice-cream. When machines are selected, the ease of cleaning should not
be overlooked. All seams should be flushed with solder. This leaves no
crevices in which bacteria and dirt can lodge, and makes cleaning easy.
The cleaning of the freezer should receive special attention.
=134. The effect of freezing and hardening on the bacterial
count.=--Authorities agree that there is an increase in the number
of organisms in ice-cream during the freezing process, as determined
by the plate method. This may be accounted for by the agitation in
the freezer breaking up the clusters of bacteria. This cluster would
give only one colony on a plate, but after being broken up might
result in several colonies. This is not a real increase in the number
of bacteria. The same holds true with other machines, such as the
clarifier.[41]
[41] Hammar, B. W., “Studies on the clarification of milk,” Ia. Exp.
Sta., Res. Bul. 28, 1916; McInerney, T. J., “Clarification of milk,” N.
Y. Cornell Exp. Sta., Bul. 389, 1917.
Ellenberger found that there were no radical changes in the total
number of bacteria in ice-cream during hardening. There seems to be a
tendency toward a slight decrease in the first two or three days with
a more noticeable increase and corresponding decrease again between
the sixth and twentieth days, after which there is only a very gradual
falling off in numbers. The lower temperatures may have a destructive
effect on some types of organisms. There may be a reorganization with
the survival of the fittest.
=135. Types of organisms in ice-cream.=--The bacterial flora of
ice-cream in summer and winter was studied by Ayers and Johnson.[42]
They divided the samples into summer and winter and the bacteria into
groups by the milk-tube method of differentiation.
[42] Ayers, S. H., and Johnson, W. T., Jr., “A bacterial study of
ice-cream,” U. S. Dept. Agr., Bul. 303, 1915.
TABLE IX
Showing the Groups of Organisms and the Percentage in Each Group
_71 Summer_ _28 Winter_
_samples_ _samples_
_per cent_ _per cent_
Acid-coagulating group 49.82 30.84
Acid-forming group 20.72 38.03
Inert group 13.98 4.81
Alkali-forming group 1.86 5.42
Peptonizing group 13.62 20.90
=136. The total-acid groups.=--“As seen in Table No. IX of the average
bacterial flora of summer ice-cream 70.54 per cent is made up of the
total group of acid-forming bacteria, and during the winter 68.87
per cent. While using the milk-tube method of differentiation the
reactions of the litmus milk tubes are recorded after 2, 5 and 14
days, and the total acid-forming group is composed of those bacteria
which produce acid in litmus milk during the 14 days’ incubation. Those
bacteria which form acid and peptonize the milk are included in the
peptonizing group. The total-acid group can be further divided into
those which produce acid and coagulate the milk and those which simply
form acid within 14 days. Since the reaction is recorded after 2, 5,
and 14 days, the rapidity of the growth of the acid-forming bacteria
can be determined, and this serves as an additional means of separating
the group. In Table No. X the percentages of the acid-coagulating and
the simple acid-forming groups of bacteria are shown, based on the 2, 5
and 14 day reaction in litmus milk.”
TABLE X
Changes in the Percentage of the Total-acid Group of Bacteria in
Ice-cream when Determined by Litmus-milk Reactions after Various
Lengths of Incubation
_Per cent reacting after_
_incubation for_
_Bacterial group_ _2 days_ _5 days_ _14 days_
_per cent_ _per cent_ _per cent_
Averages of 71 summer samples:
Acid-coagulating 26.31 41.52 49.82
Acid-forming 35.43 25.58 20.72
Average of 28 winter samples:
Acid-coagulating 8.20 25.02 30.84
Acid-forming 44.51 41.30 38.03
“An examination of Table No. X shows that among the summer samples
49.82 per cent of the bacteria produced acid and coagulated the milk
after 14 days. After 2 days 26.31 per cent produced this reaction. This
shows that a little more than half, or 52.81 per cent of the bacteria
which were in the ice-cream produced the reaction within 48 hours. The
remaining 47.19 per cent coagulated milk more slowly and may represent
a different variety of acid-forming bacteria. Turning again to the
table and considering the acid-coagulating group of the winter series,
it will be seen that of the 30.84 per cent which produced the reaction
only 8.20 per cent produced acid and coagulated milk in 2 days.
Therefore only 26.69 per cent of the acid coagulating group of the
winter samples were active enough to produce the reaction in 48 hours,
while 52.81 per cent of this group in the summer samples brought about
the change in 2 days.
“There is little to be said regarding the acid-forming bacteria which
simply produce acid. Many of them grow slowly and do not show an
acid reaction for several days in litmus milk. The milk-tube method
furnishes a means of determining the difference in the rapidity with
which the bacteria produce acid. As may be seen in Table No. X the
percentage of the acid-forming group of bacteria was highest when
determined by the 2-day reactions and lowest when based on the 5 and
14 days’ reactions. This is explained by the fact that many bacteria
have simply formed acid after two days in litmus milk and later may
coagulate or peptonize the milk, and are therefore thrown into another
group.”
=137. The inert group.=--“The inert group of bacteria in ice-cream
comprises those which produce no change in litmus milk during the 14
days’ incubation at 30° C. (86° F.). By this method of grouping there
are, of course, included in the inert group those cultures which
fail to grow in milk and tubes of litmus milk, and which would also
be included even though the lack of growth were caused by failure to
inoculate the tubes properly. However, this last possibility is small.
The inert group is of little interest, on the whole, since the bacteria
produce no apparent change in milk, and in all probability the same is
true of ice-cream.”
=138. The alkali group.=--“The alkali-forming group of bacteria is made
up of organisms capable of producing an alkaline reaction and no other
apparent change in litmus milk during the 14 days’ incubation at 30°C
(86°F). This group does not include bacteria which produce an alkaline
reaction together with visible signs of peptonization. While there are
in the literature references which deal with types of alkali-forming
bacteria, this group has rarely, if ever, been considered when the
flora of milk has been under discussion. The authors in some previous
work on bacteria in milk showed that considerable numbers of this
group were present in milk. In a later piece of work we have shown the
numbers of this type of bacteria in milk, together with some of the
cultural reactions of the alkali-forming bacteria. These bacteria,
however, give very few positive reactions with the usual cultural
media, and it is impossible to give much information regarding this
group. A detailed bacteriological and chemical study of these organisms
is under way in the research laboratories of the Dairy Division.
“It will be seen from Table XI that during the summer series of ice
cream samples the average sample contained 1.86 per cent of the alkali
group of bacteria, and during the winter series 5.42 per cent. In
general, the alkaline reaction is not noticeable until after four
or five days’ incubation in litmus milk. Occasionally, however, the
reaction is in evidence in 48 hours. This group percentage for the
summer season was 1.86 after 14 days and only 0.15 per cent based on
the 2-day reaction. Therefore, only 8.06 per cent of the bacteria of
the alkali group produce an alkaline reaction within 48 hours. Among
the samples collected during the winter season only 3.13 per cent of
the bacteria of this group were capable of producing the reaction
within two days. Whether this indicates a different variety of organism
can not be said with assurance.”
TABLE XI
Changes in the Percentage of the Alkali Group of Bacteria in
Ice-cream when Determined by Litmus-milk Reactions after Various
Lengths of Incubation
_Per cent reacting after
incubating for_
_Alkali group_ _2 days_ _5 days_ _14 days_
_per cent_ _per cent_ _per cent_
Average of 71 summer samples 0.15 1.03 1.86
Average of 28 winter samples .17 4.00 5.42
“At present we are unable to state the significance of this group of
bacteria in milk and ice-cream, but it is evident that they are not
present in ice-cream in large numbers, as are the bacteria of other
groups.
“Alkali-forming bacteria were not found in each sample examined, but
this does not prove that there were none present in the ice-cream.
Since these organisms are present in small numbers compared to the rest
of the bacteria, it is not surprising that none should be found on
plates in which the dilution had to be high in order to take care of
the large total number of organisms.”