the most interesting if not the most important group of bacteria in
ice-cream. This group consists of what are commonly known as the
putrefactive bacteria; that is to say, they attack primarily the
proteins, decomposing them into less complex organic bodies. Bacteria
of this class are usually considered undesirable in articles of food,
and it is to them that intestinal troubles are sometimes attributed,
perhaps with or without justification. Whatever their true effect is
will not be discussed in this paper, but because bacteria of this group
are looked upon with suspicion it is therefore of great importance.
“Among this group there are a large number of different types of
organisms. Many rapidly peptonize the casein of milk and render milk
alkaline or slightly acid, while others first attack the lactose and
only produce a slight peptonization after several days’ growth. From
the milk-tube method of differentiation of the bacterial groups it was
possible to gain some information as to the extent of these different
classes of peptonizers. In Table No. XII are shown the average
percentages of the peptonizing group in summer and winter samples of
ice cream. Based on the 14-day reaction among the summer samples, 13.62
per cent of the bacteria belonged to the peptonizing group. According
to the 2-day reaction, there were 5.93 per cent. Therefore 43.54 per
cent of the peptonizing bacteria were sufficiently active to produce a
peptonization within two days. Among the winter samples 34.06 per cent
of the peptonizing bacteria were sufficiently active to peptonize milk
within 48 hours. These active peptonizing bacteria are more important
than the slower-acting varieties, since their peptonizing action is
usually more complete than that of the latter-named varieties, and if
any harm is produced by this group, they are most likely to be the
organisms concerned.”
TABLE XII
Changes in the Percentage of the Peptonizing Group of Bacteria in
Ice-cream when Determined by Litmus-milk Reactions after Various
Lengths of Incubation
_Per cent reacting after
incubation for_
_Peptonizing group_ _2 days_ _5 days_ _14 days_
_per cent_ _per cent_ _per cent_
Average of 71 summer samples 5.93 9.76 13.62
Average of 28 winter samples 7.12 13.58 20.90
=140. Colon bacilli in ice-cream.=--Since the presence of colon bacilli
has been understood in water analysis to indicate fecal contamination,
many investigators and boards of health apply the same tests to milk
and naturally then to ice-cream with the same idea. In water analysis,
lactose-bile fermentation tubes are employed for the examination for
colon bacilli. By using different dilutions, the maximum number of
gas-forming bacteria in a given amount of water may be determined.
This preliminary test has to be followed by confirmatory ones in which
cultures are isolated and their characteristics studied in order to
prove the presence of colon bacilli. Ayers and Johnson used this method
to some extent but endeavored to prepare a synthetic medium which would
restrict the growth of the larger number of bacteria in ice-cream and
at the same time would allow colon bacilli to develop and produce
characteristic reactions. Ice-cream contained a much larger number of
gas-forming organisms in the summer season. A large number of media
were used in an attempt to devise a suitable medium for the detection
of Bacillus Coli in ice-cream and the results show that there is no
entirely satisfactory method known at present.
=141. Difficulties in studying the bacteriology of ice-cream.=--As has
already been pointed out, one of the greatest difficulties in studying
the bacteriology of ice-cream is the lack of a suitable culture media.
Because of the low temperature at which the ice-cream is hardened and
held, some investigators believe that there is a gradual change of
the types of organisms or the survival of the fittest. This brings up
the question as to the temperature at which the cultures should be
incubated. Until a suitable media is prepared and a uniform temperature
of incubation used, the counts of the organisms in ice-cream made by
different investigators will not be comparable.
CHAPTER XIV
_TESTING_
The determination of the composition of dairy products is a very simple
yet important part of the ice-cream business. The fat and the solids
not fat are the constituents usually determined. The most accurate
method by which to buy all raw materials is on the basis of their
composition. The finished product should be tested to determine its
composition, regardless of whether or not it is sold on this basis. The
testing of the finished product is necessary to check up the amount of
materials used. By this means an accurate cost account can be kept and
any variation in the composition of the product quickly discovered.
THE BABCOCK TEST[43]
[43] Troy, H. C., “The Babcock test and testing problems,” Cornell
Reading Course Lesson 118, 1916; Ross, H. E., and McInerney, T. J.,
“The Babcock test with special reference to testing cream,” N. Y.
Cornell Exp. Sta., Bul. 337, 1913; Hunziker, O. F., “Testing milk and
cream for butter fat,” Ind. Exp. Sta., Circ. 42, 1914.
The amount of fat in milk, cream and skim-milk can be ascertained
quickly and accurately by means of the Babcock test. The essential
requirements are that the operator be careful not to break the
glassware and that the measurements are accurately made.
=142. Testing whole milk for fat.=--The sampling is the most important
operation of the test. “The sample to be tested should be thoroughly
mixed before it is measured out. Mixing is done by shaking the vessel
in which the milk is contained, or better still, by pouring the milk
from one vessel into another. The fat in milk is lighter than the
other constituents and soon rises to the surface. Unless great care is
exercised an unfair sample will be taken. If the sample is an old one,
such as a composite sample, it should be heated to a temperature of not
over 85° F. in order to soften the fat. The sample should not be heated
above 85° F., since the fat is likely to separate in the form of an oil
and when so separated it is impossible to remix it evenly throughout
the sample.”
=143. Composite samples of milk.=--The purpose of taking composite
samples is to reduce the labor and expense of testing. The true
composite sample consists of aliquot portions of milk of several
deliveries from the same patron. Composite sample jars must have a
tight seal in order to prevent evaporation of moisture. Pint jars
sealed with glass stoppers, cork stoppers, metal caps or screw tops may
be used for this purpose. Bottles with paper caps and jelly glasses
with tin lids do not furnish tight seals; they should not be employed.
A separate jar is used for each patron and each jar must bear the
respective patron’s number. The jars should be thoroughly clean and, in
order to guard against errors, they should be arranged on convenient
shelves near the weigh-can in numerical order, grouping the jars of
patrons of the same route together. Correct composite samples may be
obtained by the use of a milk thief or a graduated pipette. If the milk
thief is used, it is inserted into the weigh-can of milk of the entire
delivery of one patron. The milk in the tube rises to the level of
that in the weigh-can. The milk thief is then emptied into the sample
jar. In case the graduated pipette is employed, a certain quantity of
milk is taken for every pound delivered by the patron (usually about
.1 cubic centimeter for every pound of milk delivered). The milk thief
is the handier instrument of the two, but when the amount of milk
delivered by different patrons varies considerably, the samples of milk
from the larger producers are often too ample to be practical.
[Illustration: FIG. 62.--Babcock milk pipette.]
Other so-called composite samples are taken by using the same measure
for all milk receipts. In this case a small dipper holding about one
ounce is commonly employed. With this dipper a sample of milk is taken
daily from the weigh-can of each patron’s milk and transferred into the
sample jar. This method of composite sampling is not mathematically
correct and the results tend to be less reliable, although experimental
data show that the results average practically the same as when aliquot
portions are taken. Evaporation causes the percentage of fat and other
solids to increase, yielding misleading tests. It also tends to dry the
milk on the surface, causing the formation of a tough, leathery layer.
In this condition it is difficult to secure a representative portion
for the test. This can be prevented: by giving the sample jar a gentle
rotary motion after each addition of milk; by replacing the stopper
properly after each addition of the milk; and by protecting the sample
from excessive heat. Fermentation may be prevented by the addition of a
small amount of preservative, such as corrosive sublimate, potassium
bichromate or formaldehyde. It is usually best to have the temperature
of the milk from 60° to 70° F. when measured into the test bottle;
however, variation within reasonable limits will not affect the test
since the coefficient of expansion of the milk is not high enough
appreciably to affect the amount measured by the pipette.
[Illustration: FIG. 63.--Babcock whole milk test-bottle.]
=144. Measuring the sample.=--The instrument for measuring the milk for
the test is called a pipette. (Fig. 62.) It has only one graduation,
17.6 cubic centimeters, equivalent to 18 grams. The sample is measured
by drawing the milk above the graduation and then placing the index
finger over the end of the pipette. By carefully releasing the finger,
the column of milk can be lowered until the bottom of the meniscus is
on a level with the 17.6 c. c. mark on the pipette. It is absolutely
necessary that the mark on the pipette be held on a level with the eye,
so as to show when the column of milk is on a level with the mark.
The milk is then transferred from the pipette to the test-bottle.
(Fig. 63.) The pipette and the test-bottle should be slanted so that
the milk will run down the bottle neck and not be forced out by the
air coming from the bottle. Whole-milk test-bottles are of two kinds,
those reading as high as 10 per cent and graduated in fifths, and those
reading as high as 8 per cent and graduated in tenths. In each case the
graduations give readings directly in terms of percentage, since the
graduated part of the neck is made to hold a column of fat which is a
definite percentage of the weight of the milk taken.
[Illustration: FIG. 64.--Acid measures for Babcock test.]
=145. Adding the acid.=--Sulfuric acid is added to the milk in
the test-bottle, by means of a special measure which has only one
graduation, 17.5 cubic centimeters. (Fig. 64.) The purpose of adding
the acid is to destroy all the milk solids except the fat, which it
does by moist combustion. In this process great heat is produced. This
is advantageous, since the fat must be kept in a liquid condition in
order to perform the test properly. The neck of the test-bottle gives
percentage readings only when the fat is in a liquid condition. In
adding the sulfuric acid, the bottle should be slanted, the same as in
adding milk. As the acid is poured in, the bottle should be revolved
so that the acid will wash down any milk that adheres to the neck. If
this is not done, the milk dries on the neck and is lost in the test;
it also causes a cloudy bottle-neck and obscures the fat column when
the test is completed. The acid and milk should be mixed thoroughly as
soon as the acid is added to the bottle, else portions of the sample
might be charred and so lock up small particles of fat. It is well
to mix the contents of the bottle for at least half a minute after
all the milk has apparently been dissolved by the acid. The mixing is
done by holding the bottle by the neck between the thumb and the index
finger, and giving it a rotary motion from the wrist (Fig. 65); if an
up-and-down motion is used, the contents of the bottle are likely to be
spilled.
The strength of the acid is reckoned in terms of its density, which
should be 1.82 to 1.83. A special instrument is used for testing the
density, and, since this instrument is seldom available in a dairy or
a creamery, one of the best ways of testing the acid is actually to
perform a test with it and note the results. The acid should be of such
strength that it will turn the contents of the bottle to a dark brown
as soon as mixed, and the mixture should turn an intense black after
standing for about one minute. The best acid is colorless, yet it may
be fairly dark and yet be fit for use. The acid should never contain
any undissolved material, since this is likely to rise with the fat and
obscure the reading.
[Illustration: FIG. 65.--Diagram showing the motion and position of a
test-bottle while mixing the milk and the acid.]
=146. Whirling the sample.=--After the acid and milk are thoroughly
mixed, the samples are ready for whirling. The centrifuges used are
of three main types (Fig. 66), those driven by hand power, by steam,
and by electricity. The steam machines usually are considered best,
since with them it is easy to maintain the proper temperature during
the process of whirling. The hand and electric machines should perform
equally as good work, provided a high enough temperature is maintained
to keep the fat in a liquid condition. The frame of the hand machine
should always be filled with hot water before the bottles are whirled.
In case of the four-bottle machines, which have no frames, the bottle
cups, which are made large for that purpose, should be filled with hot
water. Great care should be taken to have the machines balanced; by
this is meant that for every bottle on one side of the machine there
should be a bottle on the opposite side. The machines should also be
well oiled, especially those driven by steam, which, because of the
heat, soon dry out.
[Illustration: FIG. 66.--Hand and power Babcock centrifuges.]
The sample is whirled for five minutes and then filled with hot water
to the base of the neck, then whirled for two minutes and hot water
again added so as to bring the fat within the graduated part of the
neck. The sample is then whirled for one minute in order to bring all
the fat into the graduated neck. Some operators of the Babcock test
make two separate runs instead of three, filling the bottles to within
the graduated neck after the first run. While this may give fairly
good results, it is better to make three separate runs as indicated
above and fill to the base of the neck the first time. This washes the
fat free from any sediment and gives a clearer reading than would
otherwise be obtained.
=147. Reading the test.=--The sample should be read at once, before
the fat column has had time to cool. In reading, the bottle should be
held between the thumb and the index finger and the fat column should
be on a level with the eye. The fat column in a whole-milk bottle is
not large enough to be greatly affected by temperature unless it is
extremely hot or cold. With a steam centrifuge, the temperature may be
extremely high and thus the reading may be slightly increased. This
danger may be avoided by allowing the bottles to stand for a minute at
room temperature before reading. There is greater danger of reading
the fat column at too low than at too high a temperature. It does not
take long for the fat column to harden, and if the room is at all cold
it is safer to set the test-bottles in water at about 140° F., having
the water come above the fat column in the bottle. The extreme points
of the column should be included in the reading (Fig. 67) since this
method makes up very closely for minute particles of fat which are not
brought to the surface during the process of testing.
There are two methods of reading the percentage of fat in the neck of
the bottle. The first is to obtain the difference between the bottom
and the top of the fat column; if, for example, the bottom of the fat
column rests on the 1.7 per cent mark and the top on the 5.8 per cent
mark, the percentage of fat is 4.1 (5.8 - 1.7 = 4.1). The second method
of reading is to count the whole percentage and the tenth percentage
marks covered by the fat column. Some operators make use of dividers
in reading the fat column. The exact space covered is obtained, and
one point of the dividers is placed on the zero mark and the other
point against the graduated mark. The latter point will indicate the
percentage of fat. There is no objection to this method, provided the
fat column is never measured when it is above or below the graduations
on the neck of the bottle. This is often done, yet there is no
certainty that the space above or below the graduations is of the same
size as it is within the graduations; in fact, it is usually larger. It
is, therefore, easy to see the inaccurate results that may be obtained
by taking a reading when the fat column is without the graduated part
of the bottle neck.
=148. Appearance of a completed test.=--In a completed test the fat
should be straw-yellow in color; the ends of the fat column should be
clearly and sharply defined; the fat should be free from specks and
sediment; the water in the neck just below the fat should be clear;
and the fat should be in the graduated part of the neck. Some of the
defects and remedies are explained in the following paragraphs.
[Illustration: FIG. 67.--Proper way to read the percentage of fat in a
Babcock whole milk test-bottle.]
If the fat column is too dark in color, the acid may have been too
strong, or too much may have been used, or the temperature of the milk
and the acid may have been too high just before mixing, Mixing too
slowly might also permit charring of part of the fat. The charred or
darkened condition of the fat may be corrected to some extent by using
less acid, by cooling both milk and acid below 60° F. just before
mixing, and by rapid, vigorous mixing continued for about a minute
after all casein has been dissolved.
If the fat column is too light in color, the acid was either too
weak or too cold. This condition may be corrected to some extent in
succeeding tests by using more acid and by having the milk and the acid
at a slightly higher temperature when brought together.
If the acid is not of the correct strength (specific gravity 1.82 to
1.83), it will be difficult to obtain a correct test, but the trouble
may be overcome partially by using more acid when it is weak and less
when it is too strong.
=149. Care of the test-bottles.=--As soon as all the bottles are read,
they should be emptied. If allowed to stand until cold, they are more
difficult to clean. The cleaning will be accomplished much more easily
if the bottles are shaken violently up and down as the contents run
out. A viscous sediment is formed by the action of the sulfuric acid
on the milk, and the hot acid helps to loosen this if the bottles are
well shaken. All Babcock glassware should be kept clean and bright.
This can be done best by washing in hot water and washing-powder, and
then rinsing in hot water. If many bottles are employed, a block and a
top-board are very useful. The block has holes bored in it, of a size
just large enough to hold the bottles, and it may be made to contain
any desired number. The holes in the top-board are large enough to
admit the passage of the necks through them and the board rests on the
shoulders of the test-bottles. In using this block and board, a number
of bottles can be emptied at once and the hot bottles will not burn the
hands of the operator.
=150. Testing cream.=--In testing cream there are three main factors to
be considered: first, taking the sample; second, getting the correct
quantity of cream into the test-bottle; and third, correct reading of
the completed test.
=151. Cream testing apparatus.=--There are several forms and sizes
of cream test-bottles. (Fig. 68.) The six-inch nine-gram bottles are
preferable, especially for use in hand testers. This form has a scale
graduated to read from 0 to 50 per cent, the smallest scale divisions
equaling .5 of 1 per cent.
The balance for weighing cream test samples should be sensitive to .1
of a gram. There are several different types on the market.
An ordinary four-quart pail would serve as a vat in which to bring the
fat in the cream test-bottle to the proper temperature before adding
the meniscus remover and reading the test. The vat should be of such
depth that when it is nearly full of water and the cream test-bottles
are placed upright in it, the upper surface of the water and of the fat
columns will be on about the same level.
The thermometer should be of a form that registers each temperature
degree between the freezing and boiling points of water. That would
permit of its use for a variety of purposes.
[Illustration: FIG. 68.--Babcock cream test-bottles.]
=152. Sampling cream.=--Cream differs from milk in containing a higher
percentage of fat. Cream testing 30 per cent of fat would contain 70
per cent of skimmed-milk substance, or milk-serum. Before sampling, the
fat should be distributed evenly by thorough mixing or pouring. If the
cream is old or lumpy or some has dried on the container, it should be
warmed to about 95° F. and the lumps passed through a strainer before
mixing. Then about two ounces should be placed in the sample bottle.
=153. Making the cream test.=--The test sample must be weighed instead
of measured because:
1. The percentage of fat and the specific gravity of cream vary widely,
and the weight of a definite volume would vary accordingly.
2. Cream may contain bubbles of air or of carbon dioxide.
3. Cream varies so widely in viscosity (sticky quality) that the amount
delivered or the amount remaining in the pipette would be unknown.
In testing cream 9 grams are used. The bottle should be balanced on the
scales, and a 9-gram weight placed on the opposite side. The sample
is mixed thoroughly, and by means of a pipette the cream transferred
to the test-bottle until the scales exactly balance. About 9 cubic
centimeters of water are next added to the test-bottle. (This water may
be measured with sufficient accuracy in the acid measure by filling
it a little over halfway to the mark.) About 15 cubic centimeters of
the acid should be placed in the test-bottle, and the contents mixed
thoroughly. The cream and acid mixture should not turn black, but
should remain coffee color. About 15 cubic centimeters of acid give the
proper concentration to dissolve the solids not fat, since the fat
forms such a large part of the mixture and does not go into solution.
The bottles should be centrifuged and the water added exactly as in
testing whole milk.
=154. Tempering the fat and reading the percentage.=--When the last
whirling is completed, the test-bottles should be transferred to
the tempering vat containing water held at a temperature of 140° F.
The water should be tempered in advance, and should be deep enough
to surround the necks of the bottles to the top of the fat columns.
After four minutes the bottles should be taken from the water, and the
meniscus remover added at once by placing the tip of a dropping pipette
containing some of the substance against the inside of the bottle’s
neck, which is held in a slightly slanting position. The red liquid is
allowed to run slowly down the inside of the neck and spread over the
fat to a depth of about one-fourth of an inch. It should not mix with
the fat.
[Illustration: FIG. 69.--Method of reading the percentage of fat in a
Babcock cream test-bottle.]
The meniscus remover is made from a purified mineral oil that has been
colored red with alkanet root. It is sometimes called glymol. When
placed on the top of a fat column in a cream test-bottle, it flattens
the curved surface, which is known as the meniscus. The test should be
read immediately by subtracting the number on the scale at the bottom
of the fat column from the number at the line of division between the
fat and the meniscus remover. (Fig. 69.) Thus, if the bottom line of
the fat column reads 12 and the line between the meniscus remover and
the fat at the top, 39, the percentage of fat would be 27.
=155. Testing skim-milk.=--A special bottle is used for testing
skimmed-milk. (Fig. 70.) The graduated neck of the test-bottle has a
very small bore in order to measure the fat accurately. A second neck
with larger bore is attached to provide a convenient means of filling
the bottle. The smallest divisions on the scale usually indicate .01 of
1 per cent, but on some bottles .05 of 1 per cent.
[Illustration: FIG. 70.--Babcock skim-milk test-bottle.]
The same care is necessary in mixing and sampling skimmed-milk and
buttermilk that is required for whole milk, and the same pipette is
used in measuring out the sample. The skimmed-milk is added to the
test-bottle through the larger neck. Since a little more acid is
necessary thoroughly to free the fat in skimmed-milk, the measure
should be filled to about a quarter of an inch above the mark. About
one-half of the acid should first be added, and the mixture shaken
thoroughly; then add the remainder, and again shake it vigorously for
about a minute. One should avoid throwing undissolved casein into the
small neck while mixing the milk with the acid. The bottles are then
centrifuged and filled in the same manner as in testing whole milk,
except that the first whirling should be continued for ten minutes
instead of five, in order to bring up all the smaller fat globules. The
percentage of fat is read immediately on completing the final whirling.
=156. Modifications of the Babcock test for ice-cream.=--The Babcock
test as already explained cannot be used to test ice-cream, because it
contains a large percentage of sugar. This sugar would char or burn and
so interfere with the reading of the test. The following[44] are three
modifications of the Babcock test.
[44] Sproule, W. H., “Cheese and butter-making,” Ont. Agr. Coll.,
Guelph, Canada, Bul. 266, 1918.
=157. The glacial acetic and hydrochloric acid test.=--“A
representative sample of the ice-cream is taken and melted and
thoroughly mixed; a 9 gram sample is weighed into an 18 gram Babcock
cream test bottle. A mixture is prepared using equal parts of
glacial acetic acid and concentrated hydrochloric acid. Twenty cubic
centimeters of this acid mixture is added to the 9 gram sample of
ice-cream in the test bottle and is then well shaken. The bottle is
placed in a water bath of 120° F. to 130° F., and shaken at intervals
until a brown color appears. It is then placed in the Babcock
centrifuge and the test completed in the same way as for testing cream
and the reading multiplied by two.”
=158. The sulfuric acid test.=--“To make the test with sulfuric acid,
a 9 gram sample is weighed into an 18 gram test bottle. About 9 cubic
centimeters of lukewarm water is then added to dilute the sample, in
order to have about 18 cubic centimeters of mixture in the bottle. The
sulfuric acid is then added slowly, a little at a time, at minute
intervals, shaking well after each addition until a chocolate brown
color appears in the bottle. No definite amount of acid can be stated
as the quantity will vary with different ice-creams. As soon as the
chocolate brown color appears in the ice-cream a little cold water may
be added to check the action of the acid. The bottle is then placed in
the centrifuge and the test completed in the usual way. The reading is
multiplied by two.”
=159. Acetic and sulfuric acid test.=--“Weigh a 9 gram sample of
ice-cream that has been thoroughly mixed. About 9 cubic centimeters of
water are then added to dilute the sample. Add 5 cubic centimeters of
acetic acid and then add carefully 6 to 8 cubic centimeters of sulfuric
acid. Centrifuge, and then add water the same as in other tests. If
using an 18 gram bottle, multiply the reading by two, to obtain the per
cent fat in the ice cream. A 9 gram bottle which is graduated to give
the percentage of fat directly needs no correction when reading.”
=160. The lactometer.=--Because not only the fat but all the solids
are utilized in the ice-cream, it is important to know the amount of
total solids and the solids not fat in the milk. This is ascertained
by determining the specific gravity of the milk and knowing the
fat-content; the solids not fat can then be calculated. The specific
gravity of liquids is measured by an instrument called a hydrometer.
Its use is based on the fact that when a solid body floats in a liquid,
it displaces a volume of liquid equal in weight to its own. Hydrometers
are in many cases so made that the specific gravity can be read at the
point where the scale is even with the upper surface of the liquid. A
hydrometer especially adapted to milk is called a lactometer. There
are two in common use, the Quevenne and the Board of Health.
_The Quevenne lactometer_ is a long slender hollow piece of glass
weighted at the bottom to make it float in the milk in an upright
position. (Fig. 71.) The upper end is slender and contains the scale
which is graduated from 15 at the top to 40 at the bottom. Each reading
on the scale corresponds to the point marked specific gravity on a
hydrometer, except that the figures are not complete. For example, 15
on the Quevenne scale means a specific gravity of 1.015; a reading
of 30 means a specific gravity of 1.030, and so on. The Quevenne
lactometer is graduated to give correct readings at 60° F. The milk
should be at this temperature; if above or below this, a correction
must be made to the reading. The temperature should not be more than
10 degrees above or below 60° F. The correction for each degree in
variation can be made by adding or subtracting 0.1 from the lactometer
reading, as the case may be. If the temperature is above 60° F., the
correction is added to the lactometer reading; if below 60° F., it is
subtracted. The reading should be taken when the lactometer is floating
free in the milk. The scale is read exactly at the surface of the milk.
The better lactometers have a thermometer with the scale just above or
opposite the lactometer scale.
[Illustration: FIG. 71.--Quevenne lactometer.]
_The Board of Health lactometer_ is very similar to the Quevenne except
that the scale is graduated from 0 to 120. (Fig. 72.) The point on
the scale that floats at the surface in water is represented by 0,
and 100 represents the specific gravity of 1.029. On the Board of
Health lactometer the 100 degrees or divisions from 0 to 100 equal 29
divisions on the Quevenne. Therefore, one division on the Board of
Health equals 0.29 of a division on the Quevenne. To convert Board of
Health reading to Quevenne, multiply by 0.29 and to convert Quevenne to
Board of Health, divide by 0.29. The correction for temperature above
or below 60 F. is made the same as with the Quevenne, except 0.3 is
added or subtracted from the lactometer reading instead of 0.1 as with
the Quevenne.
=161. Calculating the solids not fat in the milk.=--When the lactometer
reading and the fat-content of the milk are known, there are several
formulas for calculating the solids not fat. In the following, L equals
Quevenne lactometer reading at 60° F.; F. the percentage of fat in the
milk, and S. N. F. the solids not fat in the milk.
L + 0.7F
-------- = S. N. F.
3.8
L + F
----- = S. N. F.
4
L
- + 0.2F + 0.14 = S. N. F.
4
[Illustration: FIG. 72.--Board of Health lactometer.]
=162. Testing milk for acidity.=--Several tests on the market are
used to determine the amount of acid in milk. Each is based on the
principle of chemistry, that acids and alkalies tend to neutralize each
other. The acidity of milk is of two kinds, apparent and real. The
apparent acidity is due to the acid reaction of the acid phosphates and
casein. It usually varies from .08 to .1 per cent. The real acidity
is due to the action of the bacteria on the milk-sugar. It is usually
assumed when determining the acidity of milk, that all the acidity is
due to the presence of the lactic acid.
[Illustration: FIG. 73.--Nafis acid test.]
The process by which the acidity is determined is called titration.
A known quantity of milk is placed in a cup or flask and an alkali
of known strength measured into it by means of a burette. (Fig. 73.)
The unit of measure is the cubic centimeter. The burette is usually
graduated into tenths of a cubic centimeter. The point at which all
the acid in the milk is neutralized by the alkali is told by means
of an indicator. The one commonly used is phenolphthalein. This is
colorless in the presence of acid and pink in the presence of alkali.
If two or three drops of indicator are put in the milk, the color will
not change because it is acid. When just enough alkali has been added
to neutralize the acid, the color will change to pink. The alkali
should be added slowly and gradually the acid will be neutralized by
the alkali until at last a uniform pink color appears, which will
slowly fade away. All the acid has been neutralized and the amount of
alkali used should be read from the burette, when the first change to a
uniform pink color is noted.
The different acid tests on the market are sold under various trade
names, such as Nafis, Manns, Marschalls and Farringtons. Each is based
on the same principle but uses different amounts of milk and alkali
solutions of various strengths. However, in each test the amount of
milk and strength of the alkali solution are such that the number of
cubic centimeters of alkali used are read directly as the percentage of
acid in the milk. This eliminates all calculations. If the strength and
amount of the alkali solution required to neutralize the acid in the
milk is known, and the amount of milk used, accurately measured, the
percentage of acid can be calculated.
It is a chemical fact that one cubic centimeter of a normal solution
of alkali will neutralize exactly .09 grams of lactic acid. In actual
practice an alkali solution weaker than a normal solution is employed.
This is because the latter is so strong that only a small amount
would be used, hence a small variation in the amount would make a big
variation in the final percentage. A ¹⁄₁₀ or ¹⁄₂₀ normal solution
(expressed n/10 or n/20) is commonly used. One cubic centimeter of a
n/10 alkali solution would neutralize .009 grams of lactic acid. An
example will illustrate how to figure the results. Suppose it took 4 c.
c. of n/10 alkali solution to neutralize the acid in 18 grams of milk.
What is the percentage of acidity in the milk? One cubic centimeter
of n/10 alkali will neutralize .009 grams of lactic acid. Four cubic
centimeters will neutralize 4 × .009 = .036 grams of acid; .036 grams
of acid divided by 18, the grams of milk used, multiply by 100, equals
.20 per cent acidity in the milk. This may be expressed thus:
.009 × No. c. c. alkali used
----------------------------- × 100 = per cent of acidity
number of grams material used
Then the above problem would be expressed thus:
.009 × 4
-------- × 100 = .20 per cent acidity
18
=163. Test for formaldehyde.=--Sometimes formaldehyde is added to the
milk to preserve it. It can be detected easily when making the Babcock
test. The required amount of milk is measured with the pipette into
the test-bottle and a few drops of ferric chloride added. The required
amount of sulfuric acid is next put in. If formaldehyde is present, a
lavender-colored ring will appear between the layer of acid and the
layer of milk. If the contents of the bottle are slowly mixed, the
dissolving casein will take on a lavender color. The test will not
work if the milk is too old or too much of the formaldehyde has been
added. Because of the presence of ferric salts in the sulfuric acid
as impurities, it is not always necessary to add the ferric chloride
although it is best to do so.
=164. Test for boiled milk.=--It is often desirable to know whether or
not milk has been boiled. The following test will give this result:
Two sets of reagents may be used: (1) hydrogen peroxide, potassium
iodide and starch, (2) hydrogen peroxide and paraphenylenediamine
hydrochloride. In milk there is an enzyme glactase which may be
destroyed by heat. When the milk has not been heated, this enzyme
sets free the oxygen from the oxidizing agent. In case of the first
materials, the glactase splits up the hydrogen peroxide. The free
oxygen splits up the potassium iodide and liberates free iodine. The
starch in the presence of free iodine turns blue. In the second case,
the free oxygen acts on the paraphenylenediamine hydrochloride and
turns the solution blue. In either case if a blue color results, the
milk has not been boiled. Hydrogen peroxide often contains sulfuric
acid. When this is the case, the reagent is useless for the test with
starch as the free acid would break up the potassium iodide. If this
condition exists a blue color would result, whether or not the milk had
been pasteurized.
TESTING BUTTER FOR FAT, MOISTURE, AND SALT
When large quantities of butter are used in the making of ice-cream,
it is important that it be tested. Sweet or unsalted butter is best
adapted for the making of ice-cream. If a sample is suspected or tastes
salty, a test should be made to determine the exact percentage. In
order to make cream of a desired percentage of fat, the composition of
the butter must be known.
=165. Preparing the sample.=--Experiments[45] indicate that the salt
and moisture in the butter are not uniformly distributed. This shows
the need of careful sampling and preparation of the sample before
testing. The sample should be placed in a wide-mouth ground-glass
stoppered glass jar. The bottle should be kept stoppered to prevent
evaporation. A hardwood stick is best for stirring. The bottle
containing the sample to be tested should be warmed to a temperature
of 110°-120° F. until the butter is the consistency of thick cream.
This may be done by placing the bottle in warm water. While it is being
warmed, it should be stirred to obtain a uniform mixture. It should not
be heated too much or the water and fat will separate and it is almost
impossible to mix them again. When the butter is about the consistency
of thick cream, it should be cooled and stirred thoroughly while
cooling. This insures a uniform composition in the butter. The cooling
should continue until the butter is quite firm.
[45] Lee, C. C., Hepburn, N. W., and Barnhart, F. M., “Studies of
factors influencing the composition of butter,” Ill. Exp. Sta., Bul.
137, 1909; Guthrie, E. S., and Ross, H. E., “Distribution of moisture
and salt in butter,” N. Y. Cornell Exp. Sta., Bul. 336, 1913.
=166. Testing butter for fat.=--After the sample has been prepared to
test as outlined above, 3-5 grams of this butter should be weighed
into a cream test-bottle. The addition of warm water, warm enough so
that the fat will melt, will bring the weight of the butter and water
to approximately 18 grams. Sufficient acid to give a light brown color
should be added. It will take less acid than for cream because there
are fewer solids not fat. The procedure is the same as in testing cream
for fat. After the test has been read, the percentage of fat in the
butter must be calculated.
=167. Testing butter for moisture.=--Several moisture tests[46] are on
the market. The following is a very simple one:
[46] Ross, H. E., “Butter moisture tests,” N. Y. Cornell Exp. Sta.,
Bul. 281, 1910.
The apparatus used is an alcohol lamp, iron stand, asbestos sheet, hot
pan lifter, aluminum cup for holding the sample, and a very sensitive
scale. To make the test, 10 or 20 grams of the prepared sample of
butter as described in paragraph 165, should be weighed into the
aluminum cup. The cup should be dry and about the same temperature as
the room. The alcohol lamp is then placed under the iron stand and
the asbestos sheet on the stand. The lamp is lighted and the cup put
on the asbestos sheet. It is well to light the lamp at least two or
three minutes before placing the cup on the asbestos in order to heat
it and save time. The heat of the flame may be increased or diminished
by raising or lowering the wick. The cup should always be handled with
the hot pan lifter, as by so doing it will be kept clean and errors in
weight due to dirt on the cup will be avoided.
While the sample is heating, it should be shaken from time to time
as this breaks up the blanket of casein on the surface and hastens
the escape of moisture. As soon as the casein has lost its snow-white
color, the cup should be removed from the flame. When the moisture
has all been driven from the sample, a slightly pungent odor may be
noticed. This may also be used as a guide to tell when the sample has
been heated enough. The foam begins to subside at this point. Often one
or two small pieces of casein are slow to give up their moisture. This
is indicated by the snow-white color of the pieces. Evaporation can
be hastened by shaking the sample with a rotary motion and thoroughly
mixing these pieces with the hot liquid. If this is not done, one might
have to heat the sample so long that some of the fat, which had already
given up its moisture, would volatilize.
After all the moisture is driven off, the sample is allowed to cool
to room temperature. While cooling, the cup should be covered with
something (a sheet of paper will do) to prevent the sample taking up
moisture from the atmosphere. After cooling, the cup is placed on the
scales. The sample is lighter than before heating, because it has lost
its moisture. The loss in weight divided by the weight of butter taken
gives the percentage of moisture in the sample of butter.
=168. Testing butter for salt.=--The following test has been devised
by H. C. Troy of Cornell. The materials used are: One ten cubic
centimeter burette graduated to tenths of a cubic centimeter; Babcock
milk pipette; one white cup; one pint bottle marked to show the line
at the upper surface of the liquid when the bottle contains 300 cubic
centimeters; standard tenth normal silver nitrate solution (dissolve
17.5 grams of so-called chemically pure silver nitrate in water and
make the volume up to 1000 cubic centimeters); 10 per cent solution of
potassium chromate for indicator.
To make the test, three or four ounces of the butter should be softened
by warming to a pasty condition in a fruit jar or wide-necked bottle.
It should be mixed thoroughly with a table knife or strip of wood in
order evenly to distribute the moisture. Ten grams of the mixed butter
should be weighed into a dish and washed with hot water into the pint
bottle. (If a moisture test was made on ten grams of the butter, the
substance remaining in the cup may be used for the salt test.) Enough
hot water should be added to bring the surface up to the 300 cubic
centimeters mark on the bottle, the stopper placed in the bottle and
shaken vigorously for about half a minute. The bottle should rest for
about five minutes, and a Babcock milk pipette of the watery portion
drawn (17.6 cubic centimeters) and placed in a white cup. Three or four
drops of the potassium chromate solution should be added, stirred,
and run in the standard silver nitrate solution from the burette,
with constant stirring until the color of the substance in the cup
changes to a permanent brownish red. On the burette scale the amount of
standard silver nitrate solution used may be read.
Each one-tenth of a cubic centimeter of standard silver nitrate
solution employed equals one-tenth of 1 per cent of salt in the butter.
=169. Test for viscosity.=--It is often desirable to test milk, cream
or the ice-cream mix for viscosity. There are several viscometers for
the purpose. The simplest way to determine the viscosity is to heat
and draw out the end of a pipette so that it has a very small opening.
The pipette can then be filled with the material to be tested. The
length of time required to empty the pipette determines the viscosity.
The more viscous the material, the longer it takes to run out of the
pipe. In order to make comparisons, the materials should be at the same
temperature each time. This is a very important factor.
=170. Standardization.=--One of the main requirements for a successful
ice-cream business is uniformity of quality. In order to obtain this,
it is necessary to have a product each time containing the same
percentage of fat. As it is impossible always to secure cream of a
uniform fat-content, the cream and milk used in the ice-cream must be
standardized.[47]
[47] Ross, H. E., Guthrie, E. S., and Fisk, W. W., “Practical examples
in dairy arithmetic,” Cornell Reading Course, Vol. 5, No. 98.
Standardizing milk or cream consists in raising or lowering the
fat-content to a fixed standard. This is done by adding to the
material milk or cream of a higher or lower percentage of fat. In
standardization two classes of problems are involved: first, one in
which a certain fixed amount of milk is to be made up or a certain
amount of standardized milk is desired; and second, in one in which
a certain amount of milk or cream is to be used and enough of another
product added to make the mixture test a certain percentage of fat. In
the latter case, the amount of the mixture is indefinite.
The original method of computing problems in standardization is long
and difficult, but a comparatively simple scheme has been devised by R.
A. Pearson. The method is as follows:
Draw a rectangle and place in the center of it the percentage of
fat desired. Place at the left-hand corners of the rectangle the
percentages of fat in the materials to be mixed. Subtract the number
in the center from the larger number at the left of the rectangle.
Place the remainder on the diagonally opposite right-hand corner of the
rectangle. Subtract the smaller number on the left-hand corner from the
number in the center and place the remainder on the diagonally opposite
right-hand corner of the rectangle.
The two numbers on the right-hand corners of the rectangle represent
the number of pounds of material required. If these two numbers are
added they will express the number of pounds of the mixture, which
will contain a percentage of fat expressed by the number in the center
of the rectangle. In each case the number on the right-hand corner
corresponds in fat test to the number on the left-hand corner directly
opposite.
[Illustration]
Problem: How many pounds of 40 per cent cream and 3 per cent milk
must be mixed to make milk testing 5 per cent? Using the diagram as
described, the result shown in diagram above is obtained.
This means that if 2 pounds of 40 per cent cream are mixed with 35
pounds of 3 per cent milk, the result will be a 37 pound mixture
testing 5 per cent. Answer.
Problem: How many pounds of 28 per cent cream and 3 per cent milk will
be required to make 500 pounds of a mixture testing 4 per cent? In this
problem a definite number of pounds of the mixture is required.
[Illustration]
According to the diagram, 1 pound of 28 per cent cream is required to
every 24 pounds of 3 per cent milk to make a mixture testing 4 per
cent. This would make 25 pounds of the mixture, but 500 pounds is the
amount desired. In other words, the number of pounds desired is 20
times larger than the number of pounds on hand (500 ÷ 25 = 20). The
amounts must be kept in the proportion of 1 : 24. Therefore, in order
to get a 500 pound mixture it is necessary to multiply both the 1 and
the 24 by 20. This would give a result of 20 pounds of 28 per cent
cream and 480 pounds of 3 per cent milk, which mixed will equal 500
pounds of 4 per cent milk. Answer.
This problem may also be worked by simple proportion:
1 : 25 :: x : 500
25 x = 1 × 500
25 x = 500
x = 20, number of pounds of 28 per cent cream there will be in the 500
pound mixture. Answer.
If there are 20 pounds of 28 per cent cream in the 500 pound mixture,
the remainder will necessarily be 3 per cent milk.
Therefore, 500 - 20 = 480, number of pounds of 3 per cent milk. Answer.
The number of pounds of 3 per cent milk can be found directly by simple
proportion:
24 : 25 :: x : 500
25 x = 24 × 500 = 12,000
x = 480, number of pounds of 3 per cent milk. Answer.
Proof: In working problems in standardization it is always wisest to
prove the answer, as this is the best method of checking the work for
mistakes.
According to the conditions of the problem there would be 500 pounds
of 4 per cent milk. This amount of milk would contain 20 pounds of fat
(500 × .04 = 20). According to the results the 500 pounds would be made
up of 480 pounds of 3 per cent milk and 20 pounds of 28 per cent cream.
The 480 pounds of 3 per cent milk would contain 14.4 pounds of fat (480
× .03 = 14.4). The 20 pounds of 28 per cent cream would contain 5.6
pounds of fat (20 × .28 = 5.6). 14.4 + 5.6 = 20
Since the 500 pounds contain 20 pounds of fat, and the materials of
which the 500 pounds are made up furnish the 20 pounds of fat, the
problem is worked correctly.
Problem: How many pounds of 3 per cent milk must be mixed with 150
pounds of 28 per cent cream to make a mixture testing 4 per cent? In
this problem the number of pounds to be made up is not definitely known.
[Illustration]
Working the problem by the rectangle method, 1 part of 28 per cent
cream is required for 24 parts of 3 per cent milk. According to the
terms of the problem, 150 pounds of 28 per cent cream must be used, and
this is 150 times as large as in the above proportion.
The 28 per cent cream and 3 per cent milk must be kept in the
proportion of 1 : 24, and since the amount of 28 per cent cream is to
be increased 150 times, the 3 per cent milk must also be increased 150
times. This would give 150 pounds of 28 per cent cream (1 × 150) and
3600 pounds of 3 per cent milk (150 × 24 = 3600), making in all 3750
pounds (150 + 3600 = 3750) of a 4 per cent mixture.
This problem may also be worked by simple proportion:
24 : 1 :: x : 150
x = 3600, the number of pounds of 3 per cent milk required.
Proof: The 3750 pounds of 4 per cent milk will contain 150 pounds of
fat (3750 × .04 = 150).
If the 150 pounds of 28 per cent cream and 3600 pounds of 3 per cent
milk furnish 150 pounds of fat, the problem is correct.
3600 × .03 = 108, number of pounds of fat in milk.
150 × .28 = 42, number of pounds of fat in cream.
108 + 42 = 150, number of pounds of fat in mixture. Answer.
The percentage of fat, or solids not fat, or total solids in a given
batch may be computed if the percentage composition of the materials
is known. Compute the total number of pounds of the desired material
in each of the products used and divide by the total weight of the
batch. For example, to find the percentage of fat in a batch, compute
the pounds of fat in each material and find the total number of pounds
of fat. Dividing the result by the total weight of the mix will give
the percentage of fat in the mix. The solids not fat or total solids
may be computed in the same way. By reversing these calculations, the
percentage of fat necessary in the milk or cream to yield a mixture
containing a certain percentage of fat can be computed.
[Illustration: FIG. 74.--Apparatus for testing ice-cream over-run by
the Benkendorf method.]
=171. Benkendorf[48] test for over-run in ice-cream.=--With this simple
outfit (Fig. 74), it is possible at all times and without data as to
the volume or weight of the “mix,” for the manager of the factory to
determine the over-run in any lot of ice-cream made by his employees.
[48] Benkendorf, G. H., et al., “Some improved dairy tests and
methods,” Wis. Exp. Sta., Bul. 241, 1914.
_Method of making the over-run test._
To obtain a 50 cubic centimeter sample, the metal sampler should be
pressed down into the hardened ice-cream until it is entirely below
the surface, and allowed to remain there for a minute or two, to become
chilled. Then it should be drawn out and the protruding ice-cream
removed from both ends of the sampler with a case knife or small piece
of flat metal. (When a continuous freezer is used, a metal sampler with
a closed bottom, like a cup, can be held under the spout of the freezer
until heaping full, then the surplus scraped off.)
The 200 cubic centimeter flask should be filled exactly to the mark on
the neck with hot water and the sampler held in the funnel, the stem
of which is inserted in the neck of the 250 cubic centimeter flask, a
little of the hot water poured over the sampler until the ice-cream
slips out of it, then all the remaining hot water slowly poured over
this.
The foam which appears in the neck of the 250 cubic centimeter
flask should be destroyed by adding 1 cubic centimeter (or 2 cubic
centimeters if necessary) of ether with the pipette. As soon as the
foam has disappeared, the flask may be filled with water exactly to the
250 cubic centimeter mark by means of the burette, which has previously
been filled to the zero mark.
_How to make the calculations._
The number of cubic centimeters of water and ether used to bring the
volume up to the 250 cubic centimeters mark, represents the shrinkage
which the 50 cubic centimeter sample of ice-cream has undergone when
melted. Subtracting this shrinkage from 50 gives the original volume
of the “mix” before freezing. To determine the percentage of over-run,
the number of cubic centimeters of shrinkage should be divided by the
number of cubic centimeters that were in the original mixture.
_Example:_ _Cubic centimeters_
Sample used 50
Ether used to reduce foam 1
Water used to bring to 250 c.c. mark 15.5
Water and ether used (15.5 + 1) 16.5
Volume of “mix” before freezing (50 - 16.5) 33.5
Per cent of over-run (16.5 ÷ 33.5) 49.25 per cent
=172. Test to determine the hardness of ice-cream.=--The apparatus[49]
used for determining hardness was reproduced from the description of a
similar piece of apparatus by A. E. Perkins. It consisted of a wooden
frame made of 2 × 4-inch lumber, with cross pieces on the bottom so
that it stood firmly in an upright position. A cross piece, about one
foot from the bottom of the frame, made the support for holding the
sample. At the top of this support was an adjustable wooden screw
for holding the electro-magnet. By adjustment with this screw, the
magnet could be lowered or raised several inches. This adjustment was
necessary so that the height of the needle could be made constant with
all samples. The drop frame which holds the needle and which is held up
by the magnet until the electric current from the batteries is broken,
was made from very light ³⁄₈-inch piping, the width being sufficient to
give a free drop without touching the mold, and long enough to reach
below the platform when the magnet was at its highest point. The wires
from the magnet led to a cut-off key on the side frame and from there
to a pair of dry cells from which the current was derived. The needles
were of different sizes but the same weight, thus eliminating the
necessity of adjustments to obtain constant weight. The needles were
marked from their points upward, in centimeters and fractions thereof,
to show the depth of penetration. The height of the drop was always 100
millimeters, being measured carefully with a metric rule before each
determination.
[49] Holdaway, C. W., and Reynolds, R. R., “Effects of binders upon the
melting and hardness of ice-cream,” Va. Exp. Sta., Bul. 211, 1916.
In making the determination, the frame with a suitable needle and
weights is suspended from the electro-magnet, and the material to
be tested placed in position beneath the needle, the height being
regulated as already described. The frame is then released by means of
the key. The depth of penetration is ascertained from the marks on the
needle and confirmed by measuring with the metric rule. The suspension
of the weights far below the needle brings the center of gravity of
the falling portion of the apparatus below the point of the needle,
causing the latter invariably to assume a vertical position, rendering
it much easier to ascertain the true depth of penetration than would
be the case if the point of the needle were at or below the center of
gravity. After its release by the electro-magnet, the apparatus meets
with no resistance in its fall, except that offered by the air, until
the point of the needle reaches the surface of the cream. The amount
of weight acting on the needle is known and the distance through which
it falls is constant. If, however, too much weight or too small a
needle is employed, the latter continues to sink slowly, making an
accurate reading of the depth of penetration impossible. In the reverse
case, with too large a needle or too little weight, the penetration
is of course much less and the percentage of experimental error
proportionately greater. As there was a large variation in the hardness
of the various fillers, three sets of needles were employed and in this
way much of the error was eliminated. The size of the needles were:
large ⁵⁄₁₆ inch or 7.93 millimeters, medium ⁴⁄₁₆ or 6.35 millimeters,
and small ³⁄₁₆ or 4.76 millimeters in diameter. The tests were made
by allowing each needle to penetrate the ice-cream three times. The
point of penetration was varied from center to points near the edge as
there was a possibility of the cream being harder near the edge than in
the center. The depth of penetration of each needle was expressed in
millimeters. The work was done in a cold storage with the temperature
near 0°C.
[Illustration: FIG. 75.--Mojonnier tester for fat and total solids.]
MOJONNIER TESTER
Considerable time is required to make some of the tests, after the
chemical method, such as those for solids in the different milk
products. Mojonnier Brothers have devised a test both for fat and
solids which is accurate and saves much time. A description of this
test follows. The machine is shown in Fig. 75. The numbers on the
arrows refer to numbers in the text, as follows:
(1) All tests for butter-fat are made upon this side.
(2) All tests for total solids are made upon this side.
(3) Butter-fat extraction flasks in centrifuge baskets.
(4) Eight 3½ inch aluminum dishes for butter-fat tests (the larger
ones). The one tall counterpoise counterbalances each dish. Fat
dishes have no covers.
(5) Eight 3-inch aluminum dishes for solids tests (the smaller ones).
The one short counterpoise counterbalances each dish. Cover prevents
absorption of moisture from the air during weighing. Counterpoise
balances both dish and cover.
(6) Fat vacuum oven. The temperature in this oven is maintained at
135 deg. C. Thermometer (10) extends into vacuum oven and rests on
hot plate. The mercury bulb fits snugly in removable brass mercury
well. Once a month this mercury well should be refilled with mercury.
Be careful to see that the well always forms good contact with hot
plate. Regulate temperature by rheostat (15).
(7) Cooling chamber. Water at room temperature from the tank (28) in
bottom part of the fat tester, is pumped by means of circulating pump
in power unit (20) through the flat hollow sheet brass plate inside
the cooling chambers and from there into pipe back of tester back
into tank. Operator must watch outlet on cooling chamber and see that
water is flowing at all times while the motor is turned on. If water
is not running, you may know that the water in the storage tank is
low. Keep tank filled at all times. In winter to prevent freezing,
put a gallon of denatured alcohol into tank.
(8) Solids oven. Maintained at 100 deg. C. Regulate temperature by
means of rheostat (16). Follow instructions in (6) above closely for
method of placing thermometer. Keep joints at door clean, and grease
with vaseline sliding surfaces. This insures a more perfect vacuum.
(9) A 250 deg. C. thermometer for solids oven. Wire on rubber
connections.
(10) A 250 deg. C. thermometer for fat oven.
(11) Vacuum gauge is on main suction line from vacuum pump. This
registers vacuum of either oven, or of both ovens simultaneously.
(12) Solids plate. Maintained at 180 deg. C. The thermometer can be
placed in nickel plated mercury well with base that rests directly
upon plate. See that this side is level.
(13) Fat plate. Maintained at 135 deg. C. During the evaporation of
ether from the dishes, the temperature falls. Some operators prefer
to keep temperature at 150 deg. C. to start and place dishes only
halfway upon plate. As the plate cools, the dish may be pushed over
until it is entirely upon hot plate.
(14) Rheostat for fat plate. Turning rheostat handle forward
increases temperature. Turning handle backward decreases temperature.
It is important to see that the lever on handle makes good contact
with separate buttons and not with two buttons at a time. As soon as
right button has been found that maintains constant temperature, mark
this point upon rheostat rim. In starting up tester, each day, you
may turn handle on full and then when temperature is up to within 10
degrees of right point, turn handle back to previously marked button.
Same instructions apply for all rheostats.
(15) Rheostat for fat oven.
(16) Rheostat for solids oven.
(17) Rheostat for solids plate.
(18) Handle for centrifuge.
(19) In case the operator forgets temperature and time for treating
samples at various points, he may notice the temperature and time
below each snap switch for each hot plate.
(20) The power unit consists of a high vacuum pump, a water
circulating pump, and a suction fan all driven by a single motor.
Vacuum pump must be submerged in oil furnished with tester. Fill
chamber up to air cock with oil.
(21) Automatic burettes. The cans holding the water, ammonia,
alcohol, ethyl ether and petroleum ether are placed in this order.
This is the order in which these reagents are added to the flasks
containing the weighed sample of milk. Each division delivers the
proper amount for a single extraction.
(22) Place this hood over fat dishes when evaporating off ether, so
that the suction fan may draw off ether fumes to outside of building.
(23) Fasten these legs to floor with lag screws.
(24) This side need not be fastened to floor. In case it is
necessary to take out power unit, it is necessary only to disconnect
connections in rear of machine and move this part of machine forward.
(25) The balance is the heart of the machine. Operator must keep it
level, clean and handle it carefully. Raising and lowering knife
edges must be done gradually and with care. Make it a habit of
cleaning balance daily. The weights must be kept clean, and as soon
as you notice that some of the smaller weights are wearing out, order
new ones.
(26) This cock exhausts vacuum from oven when cock (27) is closed. It
must be kept closed when vacuum is turned on oven.
(27) This cock puts vacuum from main line into vacuum oven. Set of
cocks at right is for solids oven, and at the left for fat oven.
(28) In top of fat plate holder there is a hole communicating with
suction fan on power unit. When the exhaust pipe on suction fan is
run out of window of laboratory and the hood is over the dishes, all
fumes of ether will be driven from the room.
(29) Screw stool to floor.
(30) A wash stand for washing all glassware should be provided.
=173. General preliminary information.=--In the operation of the
Mojonnier tester, several steps remain the same regardless of the
product being tested. Among these are the following:
(1) _How to use the balance._
Two types of balances are in principal use--namely, the old type with
graduated beam and rider, and the new type called “Chainomatic” with
the chain and vernier. The care to give to either type of balance is
the same. The difference is in the method of balancing the object to
be weighed, and of reading the weight. These points will be discussed
separately.
A balance is a delicate instrument, and care needs to be exercised in
its use at all times. The weights likewise require careful handling.
Lack of care in the weighing operations may lead to entirely
erroneous results, and thus defeat the object aimed at, namely,
accuracy of the tests.
The balance is inclosed in a glass case to shield it from dust,
air currents, and moisture. Perhaps the largest factor affecting
accuracy in weighing,--granting other conditions to be right, is
temperature. If the object to be weighed is of a lower temperature
than the balance case, it will weigh apparently more than its actual
weight. If of a higher temperature than the balance case, it will
weigh apparently less than its actual weight. The object should,
therefore, be as closely as possible of the same temperature as that
of the air in the balance case. The water cooled desiccator used upon
the Mojonnier tester has been designed primarily to facilitate the
equalizing of the temperature between the dishes to be weighed and
the balance case. See, therefore, that the temperature of the water
in the circulating system is as nearly as possible the same as the
temperature of the balance case.
All parts of the balance and weights should be kept free from dust.
A cover to be placed over the balance case at night serves a very
useful purpose. Use a camel’s hair brush to remove the dust from
both the balance and the weights. A small beaker partly filled with
sulfuric acid should be kept in one corner of the balance case.
Replace the sulfuric acid when it becomes saturated with moisture.
Protect the balance against vibration, and see that it is in exact
level. The air bubble in the spirit level should be in the exact
center. This can be readily accomplished by means of the leveling
screws under the balance case.
The balance should be in exact equilibrium at all times. That is, the
pointer should oscillate an equal number of divisions on each side
of zero upon the pointer scale. If the pointer swings too far to the
right, turn the adjusting screw upon the beam to the right. If it
swings too far to the left, turn the adjusting screw to the left.
Place object to be weighed upon the left hand pan, and the weights
or counterpoises upon the right hand pan. Handle the weights with
the forceps only, using the right hand. Use the left hand to release
the beam from the support, and to raise or lower the balance door.
The weights should be placed upon the pan in a systematic order,
beginning with a weight that is judged to be somewhat too heavy.
Lower weights are then tried in succession in a systematic order
until equilibrium results.
Upon the old style balance, adjustments under 5 or 10 milligrams
(depending upon the construction of the balance) are made by means of
the rider. Keep the balance door closed while the final adjustment
is being made. Determine the relation between the divisions upon
the rider beam, and the pointer scale. This relation varies with
different balances, but when once ascertained upon a given balance
it remains a constant value, and if applied in making a weighing,
a great deal of time can be saved. For example, if the pointer
oscillates six divisions to the right of zero, and four divisions
to the left, with a balance having a relation of .0002 gram to one
division upon the pointer scale, the rider is moved .0004 gram to the
right to bring the balance into equilibrium.
Upon the Chainomatic balance, adjustments under .0500 gram are made
by means of the screw and vernier. Determine the relation between the
divisions upon the vernier, and the pointer scale. If the pointer
swings too far to the right, lower the slide,--if too far to the
left, raise the slide. About .003 gram upon the vernier usually
equals one division upon the pointer scale.
Exercise great care in recording the weights. A double check should
be made by reading both the weights upon the balance pan, and the
weights that are missing from the set. The weights should be placed
upon a paper near the front of the balance case, with the values of
the weights marked upon the place where the respective weights are
kept. Remember that one misread weight will spoil an entire test.
Upon the Chainomatic balance read weights as follows:
(a) Sum of all gram weights equals whole number.
(b) Sum of 100 or multiple of 100 milligrams equals first decimal.
(c) Sum of 10 or multiple of 10 milligrams equals second decimal.
Out of a possible total of 100 milligrams, 50 milligrams are obtained
from the fractional weight, and 50 milligrams from the vernier beam.
(d) The third decimal is obtained from the vernier beam. Read the
value of the line just above the small 0 upon the slide.
(e) The fourth decimal is the value upon the slide that is in an
exact line with any given line upon the vernier beam.
(2) _Care to give to the power unit and the water circulating unit._
Keep the water tank well filled with water. Add about one quart light
machine oil to the water in the tank to keep the water pump well
lubricated. If the tester is located in a cold room in winter, add
one gallon denatured alcohol to the tank to prevent freezing.
Keep the vacuum pump chamber properly filled with the right kind
of oil. The oil should just about reach the top of the pistons, as
indicated by the glass upon the side, or cock upon the end.
Give the motor proper care. It should receive the same attention
as given to any motor, that is, it is to be kept cleaned and well
lubricated.
Should any knocks develop upon the power unit, remedy the same
immediately. The construction is very simple, and with a little
study, the care and operation of the power unit should be readily
learned.
(3) _Care to give to the vacuum ovens and coolers._
Keep sufficient mercury in the mercury well to insure good contact
between the thermometer and the mercury well. The mercury well should
rest directly upon the hot plate. Otherwise incorrect temperature
will be indicated by the thermometer. Keep the ground joint between
the lid and the oven thoroughly cleaned. In case that it is difficult
to get the proper amount of vacuum, look first to this place for
trouble. Sometimes it may be necessary to use a small amount of
vaseline, but as a rule, the best results are obtained by keeping the
ground joints thoroughly clean. Be sure that the thermometer opening,
and the openings upon the bottom of the oven are thoroughly sealed.
It may be necessary to replace the rubber tubing at these points in
case that leakage develops.
Be sure to see that the cooling desiccators are kept from freezing
temperatures. If the water in the cooling plates should freeze, it
would ruin the plates. Watch the water coming out of the coolers, in
order to be sure that the circulation is correct.
(4) _General care of the tester._
Keep the tester clean and free from the accumulation of unnecessary
material at all times. It is impossible to do accurate work if the
apparatus is not in the best of condition. All japanned parts can
be cleaned either with engine oil, applied to a clean cloth, or by
washing with good soap and water.
(5) _How to clean the dishes and the glassware._
The solids dishes should be soaked in water after the test has been
completed, and the solids then removed by means of a brush suited
to the purpose. They should then be thoroughly cleaned and dried,
and placed in the vacuum oven until required for further use. The
fat dishes should be treated with a small quantity of gasoline until
the fat is all dissolved, and this treatment repeated a second time.
Finally, the dishes are to be cleaned with a dry cloth, and placed in
the vacuum oven until needed. Do not use any water upon the fat dish.
All glassware should be washed either immediately after being used,
or it should be placed in water until washed. Extraction flasks
should be thoroughly washed with tap water and then washed out with
distilled water. If flasks become dirty, wash with washing powder
and shot, or use washing powder with a brush specially designed for
this flask. Clean pipettes with brush and water. Use washing powder,
if necessary. Rinse successively with water, alcohol, and ether, and
then dry by holding at exhaust cock leading to the vacuum oven, or
place upon pipette holder between fat oven and cooler.
(6) _How to heat the dishes before weighing._
Give both the solids and the fat dishes the same treatment before
weighing the same empty as is given to them when the same are to be
weighed with the solids or the fat respectively in the same. Do not
attempt to weigh dishes that have not been heated previous to being
weighed.
(7) _How to cool the dishes._
Transfer the solids and the fat dishes from the respective vacuum
ovens to the respective coolers, and weigh the same as rapidly as
possible. Weigh the solids dish with the cover on, and the fat dish
without any cover.
(8) _How to adjust temperatures._
The temperatures upon the two outside hot plates and the two vacuum
ovens can be closely regulated by means of the rheostats. If the
voltage is constant, the temperature will remain very near to the
point desired for a long period of time after the rheostats have been
properly adjusted. Ascertain by test, just where it is necessary to
hold the rheostat in order to get the required temperature. After
this point is once ascertained, the rheostat can be set at the point
required and the temperature allowed to come up automatically, when
starting in the morning.
(9) _How to prepare the samples._
Care and good judgment requires to be exercised in preparing samples
of the various dairy products preparatory to weighing out samples of
the same for the test. This is explained more in detail in the more
extended descriptions following the various products outlined in
these directions.
(10) _How to weigh samples for the fat test._
Several methods are in use for weighing the samples for the fat test,
depending on the product that is being tested. The weighing cross
with the short pipettes can be used successfully on a number of
dairy products. Numerous advantages are gained by using this method,
provided the product to be tested permits of its use. Five different
samples can be weighed with only six weighings, and if care is taken,
great accuracy is obtainable. Several products can be pipetted out,
taking ten grams and where possible, this is a very accurate method.
The pipettes are graduated to discharge ten grams of whole milk at
60 deg. F., allowing 15 seconds for draining the pipette after the
milk has all run out, and then blowing out the last drop of milk in
the pipette. Again, when sample shows signs of separation of fat,
the only satisfactory method is to warm up the sample until the fat
is melted, and mix thoroughly. While stirring the well mixed sample,
pipette out a sample into a cleaned, dried and weighed extraction
flask suspended from the balance beam. If flask is wet on inside it
should be weighed with cork.
(11) _Size of samples to take for the fat test._
The size of sample to use varies, depending on the product being
tested, and it ranges from one gram in the case of butter, to ten
grams in the case of raw milk. See instructions in diagram.
(12) _How to add the reagents._
The reagents should be added in the following order: Water, ammonia,
alcohol, ethyl ether and petroleum ether. The burettes upon the
dispensing cans are graduated to deliver the proper charge required.
See instruction diagram.
(13) _How to shake the flask._
If only one sample is being tested, this can be shaken by hand.
As many as four samples can be shaken at one time in the shakers
furnished with the equipment. The flask should be held with large
bulb down and small bulb extending upward. In this position they are
shaken vigorously lengthwise of flask. After shaking five or six
times, allow liquid in small bulb to run back into large bulb. Repeat
this operation at least four times. There is no danger in shaking the
samples too much, but rather of not shaking them enough.
(14) _How to centrifuge the flask._
If only one sample is being centrifuged at a time, place a
counterpoise upon the opposite side of the centrifuge in order to
balance the head. Always see that there is about the same weight upon
both sides of the centrifuge.
(15) _How to pour off the ether solutions._
Remove the cork by twisting carefully from the flask. Pour off the
ether solution as completely as possible, taking care not to allow
any of the liquid under the ether to flow out of the flask. This can
be avoided if the dividing line between the ether solution and the
remaining solution is carefully watched, while pouring off. In the
first extraction, a larger amount of the ether solution can remain in
the flask than in the second extraction. In the second extraction the
fat dish should be placed on the tester top, and the operator should
look down on the ether solution as it is being poured off, observing
the point where the ether has been all removed. By following this
method, all but one or two drops of the ether solution should be
recovered, provided the dividing line was in the right place before
pouring off.
(16) _How to bring up the dividing line._
Inability to pour off the ether solution closely is due to the fact
that the dividing line between the ether solution and the remaining
solution is too low in the lower bulb of the flask. At the end of
the first extraction, the dividing line can remain without change,
taking care to pour off the ether solution as closely as possible,
regardless of the position of the dividing line. At the end of the
second extraction, remove the stopper from the flask, and drop in
sufficient distilled water from the burette into the extraction flask
to raise the dividing line to the desired point. This should be done
just before pouring off the ether. If this procedure is followed, it
becomes possible to remove the ether almost to the last drop.
(17) _How to evaporate the ether from the dish._
It is important to maintain the proper temperature upon the outside
hot plate. If the temperature is allowed to go below 135 deg. it
takes too long to evaporate the ether solution. On the other hand,
if it rises much above 135 deg. there is danger of the ether boiling
out over the top of the dish. If the plate is too hot, it is best to
place only part of the dish in contact with the plate. We recommend
that the hood be placed over the dishes, and that the ether fumes
be blown out of the room by means of the blower. It is dangerous to
allow the ether fumes to evaporate into the working room, and besides
it makes it very unpleasant for the operator to work in contact with
these vapors.
(18) _How to heat the fat dish in the oven._
Do not transfer the fat dish to the vacuum oven until all of the
ether solution has been evaporated upon the outside plate. If this
is not done, the contents of the dish are quite likely to spatter in
the oven. It is very important to maintain the proper temperature
conditions, and also the proper vacuum upon the fat dishes, while
the same are being heated in the oven. If for any reason, there
should be difficulty in attaining either the proper heat or the
proper vacuum, the trouble should be immediately investigated and
removed.
(19) _How to weigh the fat dish._
The fat dishes are to be transferred from the vacuum oven to the
cooler, in which they are to remain for seven minutes before being
weighed. The weighing should be done as promptly as possible.
(20) _How to calculate the percentage of butter-fat._
Divide the weight of the butter-fat by the weight of the sample
taken. Multiply the result thus obtained by 100 in order to arrive at
the percentage of butter-fat in the sample.
(21) _Weight of sample to take for the solids test._
This varies with the product to be tested, ranging from .25 of a gram
in the case of sweetened condensed milk, to 2 grams in the case of
fresh milk.
(22) _How to weigh the solids sample into the dish._
The samples can be weighed from the weighing cross, or in several
cases it is advantageous to weigh the samples directly into the
solids dish.
(23) _How to add water to the samples in the dish._
For this purpose, always use best distilled water. It is well to run
a blank upon the water to determine if it is free from solid matter.
Reject any water that may contain any solid matter. Add sufficient
water to make up the total volume, not to exceed 2 cubic centimeters.
Agitate the sample with the water in the dish so that the remainder
will be uniformly distributed over the bottom of the dish.
(24) _How to treat the sample upon the outside hot plate._
It is very important to have the outside hot plate as nearly 180
deg. as possible. If the temperature is less than 180 deg. there
will be insufficient bubbling of the sample, so that the surface
will be improperly broken. If a temperature above 180 deg. is used,
there is great danger of the samples spattering out of the dish.
Heat the samples in the dish until they just begin to turn brown.
This is one of the most important steps in the entire operation, and
unless properly watched, an error may be introduced at this point.
Insufficient heating may give high results, and over heating may give
low results.
(25) _Temperature and vacuum to maintain in solids oven._
Keep the solids oven at a temperature of as nearly 100 deg. as
possible. This applies to all products to be tested. Also see that
there is at least 20 inches of vacuum upon the vacuum oven. If the
tester is properly operated, it should be possible to maintain 25
inches of vacuum at all times.
(26) _How long to retain the dish in the solids oven._
This varies with the products to be tested. The minimum time is ten
minutes and in the case of sweetened condensed milk, in order to get
absolute results, it is best to dry the samples an hour and a half.
(27) _How to cool the solids dish._
Transfer the dish from the oven to the cooler promptly, and keep the
same in the cooler for five minutes with the water circulating during
this time.
(28) _How to heat the solids dish._
Always weigh the solids dish with the dish cover upon the dish. Make
the weighings as rapidly as possible, as otherwise the sample is
quite likely to absorb moisture from the atmosphere.
(29) _How to calculate the percentage of total solids._
Divide the weight of the total solids by the weight of the sample
taken, and multiply the result by 100, which will give the percentage
of total solids in the sample.
(30) _Order of operations in testing evaporated milk for butter-fat
and total solids with Mojonnier tester._
In the following outline, the procedure described is that used in the
case of evaporated milk. The procedure in the case of other products
is much the same, but as described in directions, differences may
occur in the methods of weighing the samples; the size of the samples
to use; the quantity of water or the reagent to add; the method of
shaking, and the method of centrifuging. The outline presumes that
only one operator is doing the work. When speed is required, a helper
to the operator can materially shorten the time required. In that
case, the order of operations will need to be slightly modified.
(1) See that respective dishes have been in vacuum oven at least five
minutes while ovens are heated with vacuum on.
(2) Place respective dishes in cooling ovens, turn pump on, and set
bell for five minutes for solids and seven minutes for fat.
(3) Weigh solids dish first--being careful to put cover on dish, and
record weight and number upon laboratory report. Put dish back into
cooling oven.
(4) Weigh fat dish without cover. Record weight and number upon
laboratory report, and put fat dish back in cooling oven.
(5) Fill one 5-gram and one 1-gram pipette with milk, and place upon
weighing cross.
(6) Weigh above and note weight on laboratory report under “pipettes
plus milk” column.
(7) Transfer milk in 5-gram pipette to extraction flask, and return
empty pipette to weighing cross.
(8) Weigh again, and note weight in fat column under “pipettes.”
(9) Put above weight in solids column of laboratory report, also
under heading of “pipettes plus milk.”
(10) Transfer milk from one gram pipettes to the weighed solids dish,
and return pipette to weighing cross.
(11) Place weighing cross upon balance, weigh, and record weight
under the heading “pipettes.”
(12) Add equal volume of distilled water to solids dish, distribute
evenly, and place on solids hot plate.
(13) When evaporation has taken place, put in solids oven.
(14) Turn on vacuum and set bell for ten minutes.
(15) At this point take extraction flasks with milk in and make first
extraction, centrifuge and pour ether into fat dish.
(16) Make second extraction, same as 15.
(17) During above period solids bell will ring and solids dish should
be transferred to cooling oven, and bell set for five minutes.
(18) As soon as ether has evaporated, place dish in fat oven, turn
vacuum on, and set bell for five minutes.
(19) When solids bell rings, weigh dish and record weight.
(20) When fat test bell rings, transfer to cooling oven, and set bell
again for seven minutes.
(21) Complete subtractions on laboratory report.
(22) Weigh fat dish, turn pump off, and finish calculations.
(23) From tests obtained, determine what material to add to
standardize batch.
=174. Testing evaporated, sweetened condensed, bulk condensed milk
ice-cream (mix or melted), for fat and total solids.=--The process is
outlined in the following steps:
(1) Wash solids dishes with warm water and fat dishes with gasoline.
Dry with a towel and place into heated vacuum oven for five minutes,
with vacuum on. At the end of five minutes, put these dishes into
cooler and with pump still running, keep them there for five minutes
before weighing. Do not turn off motor until last dish is weighed out
of cooling chamber.
(2) While dishes are being heated and cooled, wash pipettes with
water, alcohol and ether, and dry by applying vacuum at exhaust cock
upon tester. Always use clean and dry pipettes for each different
sample. Aim to clean pipettes as well as all glassware, immediately
after using.
(3) It is very important to keep the extraction flasks clean. Wash
these with warm water immediately after extraction is finished. Wash
with washing powder and shot when necessary.
(4) Keep solids dishes in cooler for at least five minutes, weigh
accurately to .0001, using the proper counterpoise. Weigh solids
dishes with cover on. Keep fat dishes in cooler for seven minutes
before being weighed. Fat dishes do not have cover.
(5) Use pipettes as follows: Fill 5-gram pipettes up to 5 gram mark
for butter-fat and 1 gram pipette up to 1 gram mark for total solids.
If duplicates are to be run, fill two pipettes from the same sample.
As pipettes are filled, place lower end into cleaned and dry rubber
tubes which are pressed upon knobs at ends and center of weighing
cross. Either five or less samples for butter-fat or five or less for
total solids may be pipetted out.
(6) Weigh the cross with the pipettes containing the milk on chemical
balance accurately to .0001 gram. Run milk from pipette into proper
flask, or 3 inch dish if making solids test. The pipettes may be
distinguished by the number upon each cross. Replace pipette and
weigh again. Difference in weight gives weight of sample. Repeat
until all samples are run into proper flasks, and into weighed solids
dishes if solids are determined along with the fat.
For fat in sweetened condensed milk use a 5-gram sample. The 5-gram
pipette delivers approximately 5 grams between the 5 gram mark and
the base of the bowl of the pipette.
Some operators prefer to mix 200 grams of sweetened condensed milk
with 200 grams of water, weighing these carefully upon a Harvard trip
scale sensitive to .1 gram. In this case, care must be exercised to
obtain the exact weight of both milk and water and to stir these
thoroughly with glass or metal rod before taking sample. A tall
tumbler, a one-pound bottle or a quart cup, make good containers in
which to make mixture. A 10-gram sample of this mixture is used.
This is best weighed out by using two 5-gram pipettes on weighing
cross.
For total solids, weigh out ¹⁄₂ (.5000) to ³⁄₄ (.7500) gram of this
mixture. If the undiluted milk is used, take as nearly ¹⁄₄ (.2500)
gram as possible.
For regular 8 per cent plain bulk condensed milk, use same size
samples and treat same as evaporated milk. For 12 per cent
superheated condensed milk, mix 100 grams milk with 300 grams water
upon Harvard trip scale. Weigh 10 gram sample of this mixture into
flask for fat, and a 2 gram sample into solids dish for solids.
Multiply percentages obtained by 4 for correct percentages, when a 1
to 4 dilution is made.
=175. Fat determination.=--The following steps should be followed when
making the fat test.
(1) Remove flask from holder and run 4 cubic centimeters water (one
charge on water burette) into each flask. Be careful not to add more.
Shake well until all of sample is mixed with water. This can be done
without inserting cork.
For sweetened condensed milk, if not diluted with water, add 8 cubic
centimeters of hot water with a pipette. To get hot water, place fat
dish filled with distilled water upon solids plate. If sweetened milk
has been previously diluted with water and a 10 gram sample has been
used, it is not necessary to add water. It is very necessary to shake
the flasks containing the sweetened condensed milk very thoroughly
after the addition of each reagent. Sweetened condensed milk requires
more shaking than any other liquid milk product.
(2) Before replacing flask into holder, add 1¹⁄₂ cubic centimeters C.
P. ammonia, one charge on burette. Shake well so that all of sample
is well mixed with ammonia. This can be done without inserting cork.
(3) Add 10 cubic centimeters of 95 per cent alcohol. Insert cork,
twisting cork in firmly, using best quality corks only. Replace the
flask into flask holder. Shake thoroughly, and see that no milk
adheres to any part of flask undissolved. In case particles of milk
stick to side of flask, shake thoroughly until these are washed away.
It is of utmost importance to shake thoroughly at this point.
(4) Add 25 cubic centimeters ethyl ether, insert corks and shake
vigorously, lengthwise of flask, with liquid in large bulb of flask,
and small bulb extended upward. Stop shaking at end of five seconds
until all liquid has run into large bulb and repeat vigorous shaking
for four five-second periods.
(5) Add 25 cubic centimeters petroleum ether and shake in same way.
(6) Place extraction flasks into centrifuge and whirl for thirty
turns at speed of about 600 revolutions a minute. Have centrifuge
balanced with small oil sample bottles furnished with tester. Double
time for sweetened condensed milk.
(7) Place four 3¹⁄₂ inch dishes in line on shelf adjoining hot plate,
keeping them in order in which their weights were posted on record
sheet. Aim to have numbers on flasks correspond with number of dishes.
(8) Pour ether extraction above dividing line into proper dishes
and slide dishes over onto hot plate which should be held at a
temperature of 135 deg. C, as indicated by thermometer inserted in
nickel plated mercury well. Be careful to pour off no solid matter.
Cover dishes with hood.
(9) Repeat the extraction, shaking first to prevent formation of
precipitate, then adding successively 5 cubic centimeters of 95 per
cent alcohol, then 25 cubic centimeters ethyl ether and then 25 cubic
centimeters petroleum ether, and shake vigorously after the addition
of each of above three reagents for four five-second periods.
(10) Whirl in centrifuge for thirty turns.
(11) Move aluminum dishes back upon shelf adjoining hot plate, when
almost dry, and pour the second extraction into proper dishes. Never
pour extraction into hot dish. Remove dish from hot plate as soon as
ether is all evaporated.
(12) When all of ether has evaporated, place dishes into vacuum
oven which should have a temperature of 135 deg. C. Keep them there
for five minutes after the vacuum gauge shows at least 22 inches of
vacuum.
(13) Place dishes into cooler for seven minutes, with pump outfit
running. See that water is running through cooling plates.
(14) Place counterpoise for dish and the approximate weight for fat
on right hand balance pan.
(15) Transfer dish to left hand balance pan and weigh quickly to 0.10
milligram (0.0001 gr.).
(16) Weight of fat divided by weight of sample taken, multiplied by
100 represents percentage butter-fat.
=176. Total solids determination.=--The steps in making the test are as
follows:
(1) The temperature of the hot plate in the solids vacuum oven must
be 100 deg. C. The temperature of the outside solids plate must be
170 deg. to 180 deg. C.
(2) To weighed milk in solids dish, add about 1 cubic centimeter
water and distribute mixture evenly over bottom of dish, immediately
after weighing. For sweetened condensed milk, use hot water, or place
momentarily on hot plate and distribute evenly over dish by shaking
sidewise very carefully after cold water is added.
(3) Place not more than two dishes at once upon hot plate, which must
be perfectly level. Allow all visible moisture to evaporate. During
the evaporation turn the dishes around with crucible tongs slowly so
as to produce an even boiling over the whole bottom surface of the
dishes. The dishes must be watched carefully during the evaporation.
This step should require not more than two minutes. The end point is
reached when bubbling and crackling ceases and sample shows first
trace of brown. Vigorous boiling without spattering and complete
evaporation are fundamentally essential.
(4) Place dishes into vacuum oven which must be at 100 deg. C. and
turn on the vacuum. Heat for ten minutes. In the case of sweetened
condensed milk keep it for ninety minutes in vacuum oven, or heat for
twenty minutes and deduct 30 per cent from result. The gauge should
register not less than 22 inches of vacuum. If for any reason you
cannot obtain at least 22 inches of vacuum, then leave your dishes in
oven for twice the regular time.
(5) Remove from oven and place into cooler. Allow dishes to cool for
five minutes.
(6) Weigh dishes with covers on, being careful to weigh quickly and
very exactly.
(7) Weight of dry solids divided by weight of milk taken, multiplied
by 100, represents percentage total solids.
=177. Testing butter.=--Both the fat and the moisture may be determined
by this test. The sample may be prepared in either of two ways:
_Method I._ Remove about one-half pound butter from the different
parts of the churn or tub with a butter trier, and put this into
wide-mouthed bottle or Erlenmeyer flask fitted with rubber stopper
having a thermometer in the center of the stopper, and reaching down
into the mass of butter. Heat bottle in hot water until thermometer
reaches 40 deg. C. or 104 deg. F. If this temperature is not
exceeded, there is very little danger of the butter-fat spreading
rapidly from the curd. Shake vigorously.
_Method II._ Another very satisfactory method of preparing butter for
sampling is to put butter as it comes from churn or tub into Mason
jar, beaker, glass tumbler, or wide-mouthed bottle, any of which may
be covered tightly to prevent evaporation. Allow these to stand in
warm room or in warm water until the butter is soft enough so that it
may be stirred thoroughly with table knife, spatula, or a mechanical
stirrer. At temperature of about 75 deg. to 80 deg. F. butter stirs
into a waxy form from which water or casein will not separate. In
this form, it is put into boat or flask to be weighed.
Fat determination:
(1) If sampling method I is used, measure (about) 1 gram into weighed
butter boat. Weigh quickly and insert boat into flask. If sampling
method II is used, put about 1 gram of the butter sample into weighed
boat, weigh quickly, and insert into extraction flask.
(2) Remove flask from holder and add to extraction flask 9 cubic
centimeters hot water from aluminum dish placed on fat plate. Mark
10-gram pipette up to 9 cubic centimeter and use this for measuring
hot water. Shake vigorously so as to mix butter thoroughly with water.
(3) Before replacing flask into holder, add 1¹⁄₂. cubic centimeters
C. P. ammonia and shake thoroughly, making sure that butter is
thoroughly mixed with ammonia.
(4) Add 10 cubic centimeters of 95 per cent alcohol. Insert cork.
Replace flask into flash holder. Shake flask thoroughly with cork
inserted. Use best quality corks only.
(5) Cool flask by running cold water over lower end of extraction
flask, if flask is very hot. This is not ordinarily necessary.
(6) Add 25 cubic centimeters ethyl ether. Insert corks, shake
vigorously until all butter is dissolved out of boat. Then add 25
cubic centimeters petroleum ether and repeat operation.
(7) Centrifuge flasks, turning handle thirty turns after centrifuge
has reached a speed of about 600 revolutions a minute.
(8) Pour off extractions into proper weighed 3¹⁄₂ inch aluminum
dishes. Repeat above extraction, adding successively 5 cubic
centimeters of 95 per cent alcohol, then 25 cubic centimeters of
each ether. Excepting for very accurate work, a third extraction is
not necessary. The second extraction will remove all but .10 to .15
per cent of the butter-fat. For factory control work this would be a
good margin of safety.
(9) Evaporate off ether at 135 deg. C. on “fat plate,” and when all
of ether is off, dry fat in fat oven held at 135 deg. C. for five
minutes after the vacuum has reached at least 22 inches.
(10) Cool, weigh, and calculate percentage butter-fat as in regular
fat test.
To determine moisture in butter:
If sampling method I is used, keep butter at 140 deg. F. and mix
thoroughly and while well mixed, weigh 1 gram into the solids dish
as quickly as possible to prevent evaporation. If second method of
sampling is used, weigh 1 gram of butter into the solids dish. Heat
on hot plate at 180 deg. C. until foaming ceases, and then place
in vacuum oven held at 100 deg. C. for seven minutes. Cool, weigh
and calculate percentage solids; 100 less this figure represents
percentage moisture.
=178. Testing fresh milk, skim-milk, whey, buttermilk for fat and total
solids.=--The fat test is made as follows:
(1) Use the 10 gram pipettes for measuring out 10 grams of milk into
cleaned but not necessarily dried Mojonnier extraction flask. Use
only 10 gram pipettes furnished with tester and do not use 10 cubic
centimeter pipettes. The pipette is graduated to deliver 10 grams of
milk, after allowing all milk to run out and letting it drain for
fifteen seconds longer, then blowing gently to remove last drop.
The pipette must be perfectly clean and dry before being used. Wash
frequently with sulfuric acid, water, alcohol, and ether to insure
having a clean pipette.
(2) Make extractions exactly as in test for butter-fat in condensed
milk, excepting that no water need be added, and in second extraction
only 15 cubic centimeters of each ether need be used.
(3) Percentage butter-fat is obtained by multiplying the weight of
the extracted butter-fat by 10.
(4) If any of these products have soured badly, double the quantity
of ammonia in the regular extraction and shake until all particles
are dissolved.
Total solids determination:
Determining total solids as in evaporated milk, excepting that a
2-gram sample is weighed out, and no water need be added to spread
the milk over the bottom of the dish.
=179. Testing powdered milk, cocoa, malted milk and milk chocolate for
fat and total solids.=--
Mix the sample thoroughly, making sure that it is sufficiently
pulverized, and representative of the entire lot to be tested. In the
case of milk chocolate, pulverize the sample very thoroughly, in a
close grained mortar. Transfer the pulverized sample promptly to a
sealed jar. Mix before removing portions for testing.
Butter-fat determination:
(1) Weigh out rapidly, to prevent absorption of moisture from the
air, about 1 gram of milk powder into butter boat. In case of malted
milk, milk chocolate and cocoa, weigh out a 0.5 gram sample.
(2) Add 8.5 cubic centimeters of hot water to flask. Insert cork.
Heat flask in water boat, and shake thoroughly until the sample is
well mixed.
(3) Add 1.5 cubic centimeters (one charge) ammonia, and shake
thoroughly.
(4) Add 10 cubic centimeters of 95 per cent alcohol. Shake
thoroughly. Cool the flask, if necessary.
(5) Continue the extraction exactly as directed under the butter-fat
determination, paragraphs 4, 5, 6, and 7, inclusive.
Total solids determination:
Use .3000 gram sample. Add 2 cubic centimeters distilled water to the
sample in this dish. Otherwise continue the determination exactly as
directed under total solids determination in cheese.
=180. Testing cream for fat and total solids.=--
Mix sample thoroughly in the container. If the cream has been
homogenized, it can be weighed with the weighing pipettes as
described under 5, page 230 of these directions. If the cream is
churned or lumpy it has to be heated until the fat is all just barely
melted, and the entire mixture is uniform. Cream is a product that
is subject to many variations in composition, degree of acidity, and
physical condition. For these reasons, the operator needs to exercise
the best judgment possible. The method of operation may require, at
times, slight modification, depending on the condition of the sample.
Butter-fat determination:
(1) For cream testing under 15 per cent butter-fat, take about a 2
gram sample, using 2-gram pipette. For cream testing over 15 per
cent butter-fat take a 1-gram sample. If practicable, weigh out of
pipette as described under 5, page 230. Otherwise weigh the sample in
the butter boat, or directly into the extraction flasks, which were
previously weighed.
(2) Remove flask from the holder and add enough water to make a total
of 10 cubic centimeters. Insert cork and mix thoroughly.
(3) Before replacing flask in holder, add 1.5 cubic centimeters (one
charge) of ammonia. If the cream is sour add 3 cubic centimeters of
ammonia. This is very important.
(4) From this point to the end of the test, continue as stated on
page 231, beginning at paragraph 2 to paragraph 16, inclusive. At
the end of the second extraction it may be necessary to add quite a
little more alcohol, in order to bring the dividing line up to the
required height.
Total solids determination:
Use a 1.0 gram sample. Add 1 cubic centimeter distilled water to the
sample in the dish. Otherwise proceed exactly as directed in sections
3 to 7 of page 233.
=181. List of precautions to observe in operating Mojonnier tester.=--
(1) Before the reagents are put into the cans, be sure that the cans
are thoroughly cleaned by washing all parts, first with warm water,
then alcohol and then ether. Every third or fourth time cans are
filled, empty out last portion of reagents, and use for cleaning
purposes.
(2) The bottoms of all dishes should be kept as flat as possible. Any
bulging may be worked out by resting dishes upon marble plate in
front of balance, rubbing entire bottom surface with thumbs. Operator
should observe this every time dishes are cleaned. This is very
important.
(3) The calcium chloride in the coolers should be changed every three
or four weeks. The same calcium chloride may be used over and over by
drying the used calcium chloride in tin dishes placed upon hot plate
held at 135 deg. C. for at least five hours.
(4) The bottles should be whirled in the centrifuge until the ether
extraction is perfectly clear. About thirty turns at a normal speed
are to be recommended. For sweetened condensed milk this time must be
doubled.
(5) Be sure to keep extraction flasks perfectly clean. Wash often
with sulfuric acid and washing powder, if necessary. If particles
cling to the sides put in small shot, washing powder and hot water,
and shake thoroughly.
(6) Keep temperature regulated as nearly to standard temperature as
possible.
(7) Never pour off extraction into a hot dish. Remove dish from plate
before second extraction is run into dish.
(8) Be careful to pour off ether into dishes slowly at first and
gradually increase stream until full stream is running.
(9) In using weighing pipettes, make sure that neck of flask is free
from water when pipette is inserted.
(10) Always use clean and dried pipettes.
(11) If the samples for solids have to stand for any length of time,
add the water just as soon as they are measured out, otherwise
there is a tendency to dry and a good mixture with water cannot be
obtained. Keep dishes upon marble plate beside the balance, and not
on hot plate support.
(12) Redistill ethyl ether and petroleum ether, unless they are known
to be pure. This is unnecessary if these are bought from a reliable
firm.
(13) Make sure that water is always running through cooling plate.
Watch pipe back of cooler. If tester is located in cold room in
winter, add a gallon of denatured alcohol to tank to prevent freezing.
(14) Always aim to weigh empty dishes just before you are ready to
use them. It is not advisable to weigh them a long time before they
are used.
(15) It is fundamentally important to see that weights are read and
posted rightly. Operator should-keep his weights in systematic order
upon balance pan. When a reading is taken, it should be checked at
least three times. Learn to make weighing absolutely correct. One
figure misread may cost a month’s salary.
(16) Every operator should from time to time have a sample checked by
a thoroughly reliable laboratory. Mojonnier Bros. Company, Chicago,
Illinois, maintain such a laboratory exclusively for this purpose.
Charges very moderate.
If results on fat are high as compared with check results, the cause
may be one of the following:
(a) Not keeping bottoms of dishes flat.
(b) Improper shaking and centrifuging shown by non-fatty residue in
dish.
(c) Improper reagents (if in doubt run test upon reagents
substituting water for milk).
(d) Temperature in fat oven too low.
(e) Dirt has gotten into dish after ether was poured into it.
(f) Improper reading or posting of weights. Weights have lost weight
from use.
If results on fat are low as compared with check results, the cause
may be one of the following:
(a) Leaky corks. Use best corks obtainable.
(b) Insufficient shaking.
(c) Adding too much water.
(d) Having dividing line too low, so that too much ether is left
behind. If such is the case, add more alcohol to bring line to the
proper height, before pouring off, or make a third extraction.
(e) Too high temperature in vacuum oven.
(f) Not having water running through cooler. Tank must be kept filled.
(g) Improper reading or posting of weights.
If results on total solids are too high, as compared to check results
the cause may be one of the following:
(1) Bottoms of dishes are not kept flat.
(2) Evaporation upon solids plate has not been carried far enough. Be
sure to manipulate dish so that vigorous boiling takes place upon the
entire surface of the bottom of the dish. Do not remove dish until
all visible moisture is off or until first trace of brown coloration
appears.
(3) Improper reading or recording of weights. Weights have lost
weight from use.
(4) Dirt has fallen into dish after sample has been weighed into it.
(5) Temperature in vacuum oven is too low.
(6) Vacuum is not up to standard.
If results on total solids are too low, the cause may be one of the
following:
(1) Sample is browned too much upon outside hot plate.
(2) Temperature in vacuum oven is above 105 deg. C.
(3) Milk spattered from dish. This will not happen if temperature is
kept at 180 deg. C.
(4) Improper reading or recording of weights.
(5) Water is not running through cooler.
MOJONNIER OVER-RUN TESTER
A simple test for determining the percentage of swell or over-run has
been devised by Mojonnier Brothers. This can be used in connection with
the freezing to obtain a uniform over-run on each freezer of ice-cream.
The tester is shown in Fig. 76.
The over-run tester should be placed in the freezer-room between two
freezers, as it is designed to work both sides. The base or pedestal
should be levelled carefully as follows: Place level on surface just
over the pedestal cabinet. This should be levelled in both ways. When
pedestal is levelled, fasten securely with lag screws or bolts to
floor, using same method employed in fastening base of freezers to
floor.
In large freezer-rooms when a girl makes over-run tests and records the
over-run and advises the freezer man when to draw, one over-run tester
for each six freezers will suffice. When the freezer man makes his
own tests and records, one over-run tester will suffice for each four
freezers; that is, two freezers on either side.
=182. Adjusting cups for mix.=--The cup should be adjusted for every
batch, except in some ice-cream plants, where the butter-fat and
total solids are carefully standardized. In such cases, after the cup
has been adjusted, it will require very little, if any, adjusting
thereafter. For instance, if the mix is standardized to 8 per cent
butterfat and 33 per cent total solids and is kept at this standard by
careful testing, no adjustments need be made. The threads of the cup
are slightly greased with vaseline before being shipped. They should be
slightly greased occasionally, to facilitate free action.
[Illustration: FIG. 76.--Mojonnier over-run tester.]
The following directions should be followed:
See that the telescopic base of over-run cup is unscrewed as far as is
necessary to hold 500 gram mix (counterpoised by the 0 per cent weight.
This will be a little less than one pint). Place empty cup in suspended
cup holder. Fill dipper with the finished mix from hopper, or pipe
line, and pour in the mix until dial indicator points to 0 per cent.
The mix should contain all ingredients, namely, sugar, gelatine, and
the like.
Remove the cup of mix from the scale, place the slotted base on the
metal cleat underneath the weighing frame. Adjust this telescopic base
by turning cup around so that the top of mix comes exactly even with
the top of the cup. Carefully lock the base of the cup in position by
means of the knurled locking ring.
After the cup is adjusted, empty the mix back into the hopper over the
freezer, and rinse out the cup in a pail or five-gallon can of warm
water, making ready for the over-run determinations. There is now a
fixed relation between the capacity, and the weight of the cup and the
markings on the scale dial.
=183. Actual operation.=--A heaping cup of frozen ice-cream should
be drawn from the freezer, scraping excess off with the broad plated
knife, to an even level. Cup is placed in suspended weighing frame. The
dial indicator will immediately show the percentage of over-run. If
it points to 60, it indicates 60 per cent over-run; if to 90, 90 per
cent and so on. Two operators may use the same over-run tester at the
same time if desired, one working from either side. Repeated use of the
tester will enable the operator to handle the work with considerable
dexterity and speed.
=184. Controlling the over-run.=--While there is no set rule that can
be followed regarding the control of over-run, the following may offer
some suggestions to operators:
There are two approved methods for operating the Mojonnier ice-cream
over-run tester.
1. By a special tester, either a girl or a man whose sole duties are
to test the frozen ice-cream carefully, and notify the freezer man when
to draw the ice-cream from the freezers, that is, after it has reached
the desired over-run. In this method, one operator may run six freezers
for each over-run tester.
2. When the freezer man makes his own tests just before drawing the
ice-cream from the freezers. In order properly to control the over-run,
there should be one tester for each four freezers.
The first method applies particularly when from one to eight freezers
are used. The second method applies to large plants having more than
eight freezers in use, and where there is difficulty in procuring
adequate help, or when it becomes necessary to change help frequently.
_First operation:_ When starting to freeze a new batch, see that
over-run cup is adjusted as described.
_Second operation:_ Draw exactly five gallons of cream into the
hopper above freezers when using a ten-gallon freezer. (If larger
freezers are used, draw a volume into the hopper equal to one-half
rated capacity of freezer.) It is well to graduate and mark very
plainly the one-half capacity upon the hopper of the freezer.
_Third operation:_ Run mix into the freezers as usual, filling all
four freezers, while the freezers are running.
_Fourth operation:_ Turn on the brine and continue whipping.
_Fifth operation:_ The brine temperature and the brine pressure
should be such that about 100 per cent over-run can be obtained with
the brine turned off, and by turning on the brine again, will result
in the over-run going down too quickly. If turning on the brine after
whipping does not reduce the over-run, it is an indication of poor
brine temperature. In that case, shutting down the machine for a
short time is advisable, in order to get the brine temperature down
to a point where freezing may be done efficiently, and the yield or
over-run kept under proper control.
It is well to regulate the proper pressure according to the brine
temperature until the desirable over-run is obtained. There is a
fixed relation between these two factors, and by using the over-run
test as a guide, it is possible to adjust the pressure to the
temperature necessary to obtain the best over-run.
Brine valves on each freezer should be kept in good condition so
that when they are turned off, there is no flow of brine through
the freezer. A leaky valve may cause the over-run to refuse to go
up, due to the low temperature of the batch, thus preventing proper
whipping. Whip with the brine on until the ice-cream is quite stiff.
At this point, take test for over-run. If a satisfactory over-run
is procured, turn on brine and draw off batch. If a satisfactory
over-run has not yet been obtained, turn on the brine and continue
whipping until by repeated test, the proper over-run is obtained.
After the freezer is emptied, this operation is repeated in the same
way.
Many operators make it a point to draw off ice-cream when over-run
shows between 90 and 100. Ice-cream with over-run of more than 110
per cent is usually not a satisfactory commercial product.
_Sixth:_ Record under the proper freezer number on the freezer-room
blank, the final over-run test indicated when the cream is drawn.
Do not record any but the final result. This will form a valuable
check on the volume of ice-cream as recorded in the hardening-room.
It is possible in this way for the manager of the plant to obtain an
accurate idea of how careful the over-run has been controlled.
_Operating under the second method, or when a girl makes the over-run
tests._
Under this method, the helper in the freezer-room should not draw off
the ice-cream until it has been carefully tested and controlled. One
girl can test and control the over-run of ice-cream from six freezers
with one over-run tester, having three freezers on each side. She
can keep close watch of the frozen cream through the peep hole in
top of the freezer. As soon as the cream seems to be of the proper
consistency, a test of the over-run should be made.
_Principal causes of variation in over-run:_
The following factors influence the over-run:
(1) Milk solids in the mix
(2) Butter-fat in the mix
(3) Speed of freezers
(4) Proper ratio between solids
not fat and butter-fat
(5) Age of mix
(6) Acidity of mix
(7) Brine pressure
(8) Brine temperature
(9) Time of freezing
(10) Amount of mix drawn into freezer
(11) Blades of dasher dull or worn
(12) Slipping of belt
(13) Leaky brine valves
(14) Type of freezers
TABLE XIII
Summary of Methods of Making Fat Tests and Total Solids Tests with the
Mojonnier Tester
-----------+--------------+---------+---------+
| | | |
| | | |
| | | |
| | | |
| | | |
| | |_Size of |
_Product |_How to |_How to |sample to+
to be |prepare |weigh fat|take for |
tested_ |samples_ |sample_ |fat test_|
-----------+--------------+---------+---------+
_Fresh |Mix |Measure |10 grams |
milk_ |thoroughly |with 10 | |
| |gram | |
| |pipette. | |
| |Drain | |
| |pipette | |
| |15 | |
| |seconds | |
| | | |
| | | |
| | | |
| | | |
| | | |
-----------+--------------+---------+---------+
_Skim- |Mix | „ | „ |
milk_ |thoroughly. | | |
|Get | | |
|representative| | |
|sample | | |
-----------+--------------+---------+---------+
_Whey_ | „ | „ | „ |
| | | |
| | | |
| | | |
| | | |
| | | |
-----------+--------------+---------+---------+
_Butter- |Mix thoroughly| „ | „ |
milk_ | | | |
| | | |
-----------+--------------+---------+---------+
_Evaporated|Shake in can |Use cross|Weigh |
milk_ |very |and 5 |about |
|thoroughly| |gram |5 grams |
| |pipette | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
-----------+--------------+---------+---------+
_Bulk un- |Mix very | „ | „ |
sweetened |thoroughly. | | |
condensed |Get | | |
milk_ |representative| | |
|sample | | |
-----------+--------------+---------+---------+
_Bulk, | „ |Use cross|About 3 |
extra heavy| |and one 5|grams |
unsweetened| |gram | |
condensed | |pipette | |
milk_ | | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
-----------+--------------+---------+---------+
_Sweetened |Proceed |Use cross|About |
condensed |without |and 5 |5 grams |
milk_ |diluting. |gram | |
|Mix thoroughly|sample | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
-----------+--------------+---------+---------+
_Ice-cream |Mix |Use cross| „ |
mix_ |thoroughly. |and 5 | |
|Heat slightly |gram | |
|if necessary |pipette | |
|to melt fat |and weigh| |
| |rapidly | |
| |or weigh | |
| |directly | |
| |into | |
| |flask | |
| | | |
| | | |
-----------+--------------+---------+---------+
_Cream |Mix |Use weigh|About 2 |
testing |thoroughly. |cross |grams |
less than |Heat slightly |with 2 | |
25% b. f._ |if necessary |gram | |
|to melt fat |pipette. | |
| |If | |
| |necessary| |
| |use boat | |
| |or weigh | |
| |directly | |
| |into | |
| |flask | |
| | | |
-----------+--------------+---------+---------+
_Cream | „ | „ |About |
testing | | |1 gram |
more than | | | |
25% b. f._ | | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
-----------+--------------+---------+---------+
_Malted |Mix |Use |.5 gram |
Milk_ |thoroughly. |butter | |
|Get |boat, or | |
|representative|weigh | |
|sample |directly | |
| |into | |
| |flask | |
| | | |
-----------+--------------+---------+---------+
_Milk |Pulverize in | „ | „ |
chocolate_ |close grained | | |
|mortar. | | |
||Transfer to | | |
|sealed jar | | |
-----------+--------------+---------+---------+
_Cocoa_ |Mix | „ | „ |
|thoroughly. | | |
|Get | | |
|representative| | |
|sample | | |
-----------+--------------+---------+---------+
_Cheese_ |Pulverize in | „ |1.0 gram |
|close grained | | |
|mortar. | | |
|Transfer to | | |
|sealed jar | | |
-----------+--------------+---------+---------+
_Butter_ |See detailed |Use | „ |
|directions |butter | |
| |boat | |
| | | |
| | | |
| | | |
| | | |
-----------+--------------+---------+---------+
_Skimmed- |Pulverize in |Use |About 1 |
milk |close grained |butter |gram |
powder_ |mortar. |boat or | |
|Transfer to |weigh | |
|sealed jar |directly | |
| |into | |
| |flask | |
| | | |
-----------+--------------+---------+---------+
_Whole-milk| „ | „ | „ |
powder_ | | | |
| | | |
-----------+--------------+---------+---------+