Laboratory guide in market milk

Preface

The production and handling of clean milk is based on scientific principles. It is true that many of these principles are simple in their ^application and oftentimes on account of their simplicity they are overlooked and neglected. It is the purpose of this laboratory guide to enable the student to better understand the application of science to clean milk production, and to impress on his mind the necessity for attention to detail in this branch of Dairy Industry.

Our ideas concerning the best methods of clean milk production are constantly changing. The Author recognizes that this will necessitate frequent revision of this book and an effort will be made to keep this laboratory guide thoroughly up-to-date.

H. E. Ross.

Dairy Laboratories

New York State College of Agriculture

at Cornell University

It is generally accepted that clean milk means milk which is free from microorganisms or the products of their action. It is possible to conceive of milk being impure from something other than microorganisms or their products, such as the addition of some poisonous substance to milk. The possibility of such contamination is, however, so rare and so remote that the words "imptire milk," have come to mean that which is affected by the action of microorganisms.

For this reason all operations and experiments performed in a laboratory should be done in such a way as to prevent bacterial contamination, and all dairy utensils with which the milk comes in contact should be rendered sterile so far as possible. This can be done by thoroughly scalding all dairy apparatus, or better still by exposing them to live steam for not less than one hour. If the dairy utensils are scalded by means of hot water, the temperature of the water should be not less than i8o°F. and it should be as near the boiling point as possible.

Dippers and other dairy utensils in which milk is handled, or which comes in contact with the milk in any way, should not be laid on the floor and then placed in the milk. Care should be taken not to touch the surfaces of dairy utensils, such as coolers, bottle fillers and so forth, with the hands. Water even in small amounts, may, if allowed to enter milk, cause it to putrefy.

Cleaning Dairy Utensils

Dairy utensils must be thoroughly cleaned if milk is to be handled in a sanitary manner. The proper way in which to clean a dairy utensil is to first rinse it with cold or luke-warm water, preferably the latter. This removes most of the milk from the utensil and prevents later cooking of the albimien of the milk on to the apparatus, when it is scalded or sterilized. The utensil should next be thoroughly washed by means of a brush and hot water in which there has been dissolved some good washing powder. An excessive amount of powder is not necessary, a tablespoonful to a pail of hot water is usually sufficient. The utensil should then be scalded in hot water, and if possible, exposed to the action of live steam for not less than one hour, thereby rendering the utensil as sterile as possible. It should be kept in a place where it will not become recontaminated.

EXPLANATION OF EXERCISE I

In studying any dairy utensil, it should be noted whether the utensil is so arranged and constructed as to best fulfill the purpose for which it is intended. All dairy utensils should be as simple as possible in construction. They shovild have no seams and crevices into which milk can collect. Any cracks or seams in copper or tin surfaces should be well flushed with solder. AH parts should be accessible so that they may be thoroughly cleaned. They should be strong and durable and at the same time, any extra metal or other material is objectionable. On account of its durability and the ease with which it may be cleaned, metallic is usually preferable to wooden construction.

When possible, metallic construction should be of some non-rustable material.

EXERCISE I A Study of Dairy Apparatus

1. Bottle Fillers — Study the tubes of the different fillers used. Show by drawings how the milk flows from the tank through the tube into the bottle, and the provision made for removing air and surplus milk from the bottle.

Pasteurizers — Show by cross-sectional drawing the method of operation of a holder pasteurizer and a flash pasteiuizer.

2. Clarifiers — Explain the action of a centrifugal clarifier. In each case show by means of a drawing the chief differences between the inner device of the clarifier and a cream separator of the same make. Also compare the relative speed of clarifiers and separators of the same make and having the same capacity per hour.

3. Coolers — Make drawings of a conical and tubular type of cooler and explain the action of each.

In case of the tubular cooler, show its connection with a brine barrel and indicate the relative position of the cooler, brine barrel and pump.

4. Milk Bottles — Make drawings of two different styles of milk bottles.

DIRECTIONS FOR STANDARDIZATION

The process of standardization consists in raising or lowering the percentage of fat in milk or cream to a definite standard. This is done by adding milk of a higher or lower fat content, than the material which is being standardized.

Some market milk does not normally contain sufficient fat to be satisfactory to the consimier. In order to make this milk satisfactory the dealer oftentimes standardizes it by the addition of cream.

Since the law states that unadvdterated milk is milk to which nothing has been added or anything taken aw&,y, there has been raised some slight question as to the legality of the process of standardization. However, the addition of cream to milk increases its value, so that no serious objection has been raised to that part of the process. One would, however, have no right to reduce the fat content of milk by the addition of skimmed milk, as this would be essentially the same as removing fat from the milk.

At the present time much of the cream sold is paid for on a basis of its fat content and for this reason a knowledge of standardization is useful to the cream shipper. If a dealer receives a certain price for cream containing a definite percentage of fat it is desirable to have no more or no less fat than the percentage agreed upon. If there is more fat than the contract calls for, the seller loses, and if there is less fat the buyer loses.

In standardization there are two classes of problems involved: first, one in which two products containing a known percentage of fat are mixed to make a definite amount of milk or cream containing a fixed percentage of- fat, and second, one in which a definite amount of milk or cream of a known percentage of fat is used and enough of some other product added to make the resulting mixture test the desired percentage of fat. In the first case the amount is definite, and in the second case it is indefinite.

The usual method of working standardization problems is quite difficult, but Pearson has devised a method which greatly simplifies the computation. It is as follows: Draw a rectangle and place in the center of it the percentage of fat desired. On the left hand comers place the percentages of fat in the materials to be mixed. It is customary to place the larger percentage on the upper left hand corner and the smaller percentage on the lower left hand comer, although the position of these numbers might be reversed without affecting the results. Subtract the smaller number on the left hand comer of the rectangle from the number in the center and place the remainder on the diagonally opposite right hand comer. Then subtract the number in the center of the rectangle from the larger number on the left hand comer and place the remainder on the diagonally opposite right hand comer. The two mmibers on the right hand comers of the rectangle represent the mmiber of potmds of materials required. The sum of these two numbers will be a mixtiu"e containing the desired percentage of fat, expressed by the number in the center of the rectangle.

In each case the nimiber on the right hand comer of the rectangle corresponds to the number on the left hand comer directly opposite.

A few concrete examples will illustrate the rectangle method of working problems in standardization.

Problem I. How many pounds of 23% cream and 3% milk will be required to make 500 pounds of an 18% cream? Using our diagram as described above we have the following results:

These results mean that if five povmds of 3% milk were mixed with IS poimds of 23% cream the result will be 20 pounds of a mixture testing 18%. The amount of the mixture desired was 500 pounds, which is twenty-five times the amount obtained with the rectangle method (500 -^ 20 = 25). If we multiply the numbers on the upper and lower right hand comers of the rectangle by twenty-five we will obtain respectively the pounds of 23% cream and 3% milk required to make 500 pounds of an 18% mixture. These are 375 potmds of 23% cream (15 x 25 = 375), and 125 pounds of 3% milk (5x25 = 125).

The problem may also be worked by simple proportion : 5:20 :: X : 500

20X = 7500 X = 375 pounds of 23% cream.

lO

In the above problems the amount of the mixture desired is definite.

In working problems in standardization it is wisest to prove the answer as this will show if the results are correct. While proving a problem will point out errors it will not show where mistakes have been made. The proof of the above problem is as follows:

Proof:

It is desired to make 500 pounds of an 18% mixture which would necessarily contain 90 pounds of fat (500 X .18 = 90). According to our computations the 500 pounds of 18% cream will consist of 125 pounds of 3% milk and 375 pounds of 23% cream. If these materials furnish 90 pounds of fat, the problem is worked correctly. One hundred twenty-five pounds of 3% milk will contain 3.75 pounds of fat: (1.25 X .03 = 3.75). Three hundred seventy-five pounds of 23% cream will contain 86.25 pounds of fat (375 X .23 = 86.25), 86.25 -f- 3.75 = 90 pounds of fat.

In the following problem the amount of mixture to be made up is indefinite.

Problem 2 :

How much 23% cream must be mixed with 500 pounds of 3% milk to make a mixture testing 1 8% ? Using our diagram according to the directions previously given we have the following results:

These results mean that we must mix the materials in the proportion of 15 pounds of 23% cream to five pounds of 3% milk to make an 18% mixture. According to the conditions of the problem we must use 500 pounds of 3% milk which is 100 times as large as the amount given in the above proportion (500 -^ 5 = 100). The 23% cream and the 3% milk must be kept in the proportion of 15:5 and if the 3% milk is increased one hundred times the 23% cream must be increased the same number of times. This would give 1500 pounds of 23% cream (15 X 100 = 1500), which should be added to the 500 pounds of 3% milk, giving 2000 pounds of an 18% mixture. The problem may also be worked by simple proportion.