The improved form of milking-pail shown in fig. 1 has rests or brackets,
which the milker when seated on his stool places on his knees; he thus
bears the weight on his thighs, and is entirely relieved of the strain
involved in gripping the can between the knees. The milk sieve or
strainer (fig. 2) is used to remove cow-hairs and any other mechanical
impurity that may have fallen into the milk. A double straining surface
is provided, the second being of very fine gauze placed vertically, so
that the pressure of the milk does not force the dirt through; the
strainer is easily washed. The cheese tub or vat receives the milk for
cheese-making. The rectangular form shown in fig. 3 is a Cheshire
cheese-vat, for steam. The inner vat is of tinned steel, and the outer
is of iron and is fitted with pipes for steam supply. Round cheese-tubs
(fig. 4) are made of strong sheets of steel, double tinned to render
them lasting. They are fitted with a strong bottom hoop and bands round
the sides, and can be double-jacketed for steam-heating if required.
Curd-knives (fig. 5) are used for cutting the coagulated mass into cubes
in order to liberate the whey. They are made of fine steel, with sharp
edges; there are also wire curd-breakers. The object of the curd-mill
(fig. 6) is to grind consolidated curd into small pieces, preparatory to
salting and vatting; two spiked rollers work up to spiked breasts.
Hoops, into which the curd is placed in order to acquire the shape of
the cheese, are of wood or steel, the former being made of well-seasoned
oak with iron bands (fig. 7), the latter of tinned steel. The cheese is
more easily removed from the steel hoops and they are readily cleaned.
The cheese-press (fig. 8) is used only for hard or "pressed" cheese,
such as Cheddar. The arrangement is such that the pressure is
continuous; in the case of soft cheese the curd is merely placed in
moulds (figs. 9 and 10) of the required shape, and then taken cut to
ripen, no pressure being applied. The cheese-room is fitted with
easily-turned shelves, on which newly-made "pressed" cheeses are laid to
ripen.
[Illustration: FIG. 1.--Milking-Pail.]
[Illustration: FIG. 2.--Milk Sieve.]
[Illustration: FIG. 3.--Rectangular Cheese-Vat.]
[Illustration: FIG. 4.--Cheese-Tub.]
[Illustration: FIG. 5.--Curd-Knives.]
[Illustration: FIG. 6.--Curd-Mill]
[Illustration: FIG. 7.--Hoop for Flat Cheese.]
[Illustration: FIG. 8.--Cheese-Press.]
[Illustration: FIG. 9.--Cheese-Mould (Gervais).]
[Illustration: FIG. 10.--Cheese-Mould (Pont l'Eveque).]
[Illustration: FIG. 11.--Milk-Pan.]
[Illustration: FIG. 12.--Skimmer.]
In the butter dairy, when the centrifugal separator is not used, milk is
"set" for cream-raising in the milk-pan (fig. 11), a shallow vessel of
white porcelain, tinned steel or enamelled iron. The skimming-dish or
skimmer (fig 12), made of tin, is for collecting the cream from the
surface of the milk, whence it is transferred to the cream-crock (fig.
13), in which vessel the cream remains from one to three days, till it
is required for churning. Many different kinds of churns are in use, and
vary much in size, shape and fittings; the one illustrated in fig. 14 is
a very good type of diaphragm churn. The butter-scoop (fig. 15) is of
wood and is sometimes perforated; it is used for taking the butter out
of the churn. The butter-worker (fig. 16) is employed for consolidating
newly-churned butter, pressing out superfluous water and mixing in salt.
More extended use, however, is now being made of the "Delaiteuse" butter
dryer, a centrifugal machine that rapidly extracts the moisture from the
butter, and renders the butter-worker unnecessary, whilst the butter
produced has a better grain. Scotch hands (fig. 17), made of boxwood,
are used for the lifting, moulding and pressing of butter.
[Illustration: FIG. 13.--Cream-Crock.]
[Illustration: FIG. 14.--Churn.]
[Illustration: FIG. 15.--Butter-Scoop.]
In the centrifugal cream-separator the new milk is allowed to flow into
a bowl, which is caused to rotate on its own axis several thousand times
per minute. The heavier portion which makes up the watery part of the
milk flies to the outer circumference of the bowl, whilst the lighter
particles of butter-fat are forced to travel in an inner zone. By a
simple mechanical arrangement the separated milk is forced out at one
tube and the cream at another, and they are collected in distinct
vessels. Separators are made of all sizes, from small machines dealing
with 10 or 20 up to 100 gallons an hour, and worked by hand (fig. 18),
to large machines separating 150 to 440 gallons an hour, and worked by
horse, steam or other power (fig. 19). Separation is found to be most
effective at temperatures ranging in different machines from 80 deg. to
98 deg. F., though as high a temperature as 150 deg. is sometimes
employed. The most efficient separators remove nearly the whole of the
butter-fat, the quantity of fat left in the separated milk falling in
some cases to as low as 0.1. When cream is raised by the deep-setting
method, from 0.2 to 0.4% of fat is left in the skim-milk; by the
shallow-setting method from 0.3 to 0.5% of the fat is left behind. As a
rule, therefore, "separated" milk is much poorer in fat than ordinary
"skim" milk left by the cream-raising method in deep or shallow vessels.
The first continuous working separator was the invention of Dr de Laval.
The more recent invention by Baron von Bechtolsheim of what are known as
the Alfa discs, which are placed along the centre of the bowl of the
separator, has much increased the separating capacity of the machines
without adding to the power required. This has been of great assistance
to dairy farmers by lessening the cost of the manufacture of butter, and
thus enabling a large additional number of factories to be established
in different parts of the world, particularly in Ireland, where these
disc machines are very extensively used.
[Illustration: FIG. 16.--Butter-Worker.]
[Illustration: FIG. 17.--Scotch Hands.]
[Illustration: FIG. 18.--Hand-Separator.]
The pasteurizer--so named after the French chemist Pasteur--affords a
means whereby at the outset the milk is maintained at a temperature of
170 deg. to 180 deg. F. for a period of eight or ten minutes. The object
of this is to destroy the tubercle bacillus, if it should happen to
exist in the milk, whilst incidentally the bacilli associated with
several other diseases communicable through the medium of milk would
also be killed if they were present. Discordant results have been
recorded by experimenters who have attempted to kill tubercle bacilli in
milk by heating the latter in open vessels, thereby permitting the
formation of a scum or "scalded layer" capable of protecting the
tubercle bacilli, and enabling them to resist a higher temperature than
otherwise would be fatal to them. At a temperature not much above 150
deg. F. milk begins to acquire the cooked flavour which is objectionable
to many palates, whilst its "body" is so modified as to lessen its
suitability for creaming purposes. Three factors really enter into
effective pasteurization of milk, namely (1) the temperature to which
the milk is raised, (2) the length of time it is kept at that
temperature, (3) the maintenance of a condition of mechanical agitation
to prevent the formation of "scalded layer." Within limits, what a
higher temperature will accomplish if maintained for a very short time
may be effected by a lower temperature continued over a longer period.
The investigation of the problem forms the subject of a paper[12] in the
17th _Annual Report of the Wisconsin Agricultural Experiment Station_,
1900. The following are the results of the experiments:--
1. An exposure of tuberculous milk in a tightly closed commercial
pasteurizer for a period of ten minutes destroyed in every case the
tubercle bacillus, as determined by the inoculation of such heated
milk into susceptible animals like guinea-pigs.
2. Where milk is exposed under conditions that would enable a pellicle
or membrane to form on the surface, the tubercle organism is able to
resist the action of heat at 140 deg. F. (60 deg. C.) for considerably
longer periods of time.
[Illustration: FIG. 19.--Power Separator.]
3. Efficient pasteurization can be more readily accomplished in a
closed receptacle such as is most frequently used in the commercial
treatment of milk, than where the milk is heated in open bottles or
open vats.
[Illustration: FIG. 20.--Refrigerator and Can.]
4. It is recommended, in order thoroughly to pasteurize milk so as to
destroy any tubercle bacilli which it may contain, without in any way
injuring its creaming properties or consistency, to heat the same in
closed pasteurizers for a period of not less than twenty minutes at
140 deg. F.
Under these conditions one may be certain that disease bacteria such
as the tubercle bacillus will be destroyed without the milk or cream
being injured in any way. For over a year this new standard has been
in constant use in the Wisconsin University Creamery, and the results,
from a purely practical point of view, reported a year earlier by
Farrington and Russell,[13] have been abundantly confirmed.
[Illustration: FIG. 21.--Cyclindrical Cooler or Refrigerator.]
Dairy engineers have solved the problem as to how large bodies of milk
may be pasteurized, the difficulty of raising many hundreds or thousands
of gallons of milk up to the required temperature, and maintaining it at
that heat for a period of twenty minutes, having been successfully dealt
with. The plant usually employed provides for the thorough filtration of
the milk as it comes in from the farms, its rapid heating in a closed
receiver and under mechanical agitation up to the desired temperature,
its maintenance thereat for the requisite time, and finally its sudden
reduction to the temperature of cold water through the agency of a
refrigerator, to be next noticed.
Refrigerators are used for reducing the temperature of milk to that of
cold water, whereby its keeping properties are enhanced. The milk flows
down the outside of the metal refrigerator (fig. 20), which is
corrugated in order to provide a larger cooling surface, whilst cold
water circulates through the interior of the refrigerator. The conical
vessel into which the milk is represented as flowing from the
refrigerator in fig. 20 is absurdly called a "milk-churn," whereas
milk-can is a much more appropriate name. For very large quantities of
milk, such as flow from a pasteurizing plant, cylindrical refrigerators
(fig. 21), made of tinned copper, are available; the cold water
circulates inside, and the milk, flowing down the outside in a very thin
sheet, is rapidly cooled from a temperature of 140 deg. F. or higher to
1 deg. above the temperature of the water.
[Illustration: FIG. 22.--Butyrometer.]
The fat test for milk was originally devised by Dr S. M. Babcock, of the
Wisconsin, U.S.A., experiment station. It combines the principle of
centrifugal force with simple chemical action. Besides the machine
itself and its graduated glass vessels, the only requirements are
sulphuric acid of standard strength and warm water. The machines--often
termed butyrometers--are commonly made to hold from two up to two dozen
testers. After the tubes or testers have been charged, they are put in
the apparatus, which is rapidly rotated as shown (fig. 22); in a few
minutes the test is complete, and with properly graduated vessels the
percentage of fat can be read off at a glance. The butyrometer is
extremely useful, alike for measuring periodically the fat-producing
capacity of individual cows in a herd, for rapidly ascertaining the
percentage of fat in milk delivered to factories and paying for such
milk on the basis of quality, and for determining the richness in fat of
milk supplied for the urban milk trade. Any intelligent person can soon
learn to work the apparatus, but its efficiency is of course dependent
upon the accuracy of the measuring vessels. To ensure this the board of
agriculture have made arrangements with the National Physical
Laboratory, Old Deer Park, Richmond, Surrey, to verify at a small fee
the pipettes, measuring-glasses, and test-bottles used in connexion with
the centrifugal butyrometer, which in recent years has been improved by
Dr N. Gerber of Zurich.