The book of ice-cream

Several milk products are commonly used in ice-cream, namely: whole and skimmed-milk, cream, condensed milk, evaporated milk, milk powder and butter. These may be utilized singly or in combinations. The most important characteristic of the milk products is their flavor which should be clean and sweet; if not, it is likely to impart its undesirable flavor to the ice-cream. Much might be written on the production, care and composition of the milk and cream. Space will not permit this, but the essential factors as related to ice-cream will be discussed.

5. Method of securing supply.

—The ice-cream industry offers an entirely different problem from the other branches of the dairy industry in relation to securing a supply of milk and cream. This is due to the location. There are usually brokers or commission men who are willing to handle butter, cheese, condensed milk and other dairy products which are not comparatively as perishable as ice-cream. Therefore, the butter, cheese, and condensed milk plants are located where they can secure easily a supply of raw milk, which is in the country. On the other hand, there are no brokers or commission men who handle ice-cream; therefore, the ice-cream is sold directly to the retailer or consumer. Because of the ease of delivery, the ice-cream plant is located in the center of population, namely, the city or village. It has not proved satisfactory, either from the view point of quality or cost of production, to make the ice-cream near the supply in the country and ship the finished product to the city.

Due to the location of the ice-cream plant in the city, there are four ways of securing the raw materials:

1. Buy milk and cream from dealer.

2. Operate creamery in country and get supply from it.

3. Use surplus from other dairy operations, and purchase necessary balance.

4. Use of homogenized or emulsified milk and cream.

Each ice-cream concern will have to decide, after carefully considering all the factors, which method is best adapted for its use. Each has its advantages and disadvantages.

Buying milk and cream from dealer.

Advantages:

1. No surplus to dispose of.

2. Minimizes labor in the ice-cream plant.

3. Requires less capital.

Disadvantages:

1. Uncertainty of cream supply.

2. No control of quality.

3. Higher cost of cream.

4. No control of fat-content of cream.

5. Must have separate supply of condensed milk.

6. At mercy of cream dealer.

7. Difficult to dispose of any surplus.

Operating creamery in country and getting supply from it.

Advantages:

1. Certain of known supply.

2. Better control of quality.

3. Easy to dispose of any surplus.

4. Usually a cheaper supply.

5. Can secure cream of desired fat-content.

6. Can pay patrons better price for milk.

7. May make own supply of condensed milk.

8. More independent.

Disadvantages:

1. Requires more capital.

2. Requires more labor.

3. Requires more management.

4. Must deal directly with the dairy-men.

5. Transportation.

6. Must find suitable location.

Using surplus from other dairy operations and purchasing necessary balance.

Advantages:

1. Makes an outlet for surplus.

2. Economy of delivery.

Disadvantages:

1. May make too large a business.

2. May not have necessary equipment, especially refrigerator.

3. May not be able to purchase necessary balance of supply. Disadvantages same as buying from dealer.

4. If side line, may not give it proper attention.

5. May not have surplus only part of year so balance of year do not care to operate.

Use of homogenized or emulsified milk and cream.

Advantages:

1. When big demand can quickly make supply of cream.

2. Sweet cream can be secured in localities where it can not be produced easily, especially the South.

3. Does not necessitate carrying a large surplus of cream.

4. Usually a cheap supply of cream.

Disadvantages:

1. Tendency to try to use butter and milk products of inferior quality.

2. Because of the physical nature of homogenized cream, try to use less fat in it.

6. Quality of milk and cream desired.

—Regardless of how obtained, the cream and milk should be of the desired quality for ice-cream manufacture. The cream should be clean flavored and sweet. In some plants, when the cream is slightly sour, a neutralizer is added, but this practice should not be followed. Better care, better holding methods or both should be employed to insure sweet cream. The refrigerated room in which milk and cream are stored in a large ice-cream plant is shown in Fig. 1. Cream for ice-cream-making should not have more than 0.24 per cent of acid by the acid test. (For use of acid test, see Chapter XIV.) In order to insure sweetness, cream is usually pasteurized. Pasteurization⁠[2] is heating to a temperature sufficiently high, usually 145° F. and held at this temperature for a sufficient period, usually thirty minutes, to kill most of the organisms in the milk and then rapidly cooling to 50° F. or below. When pasteurized cream and milk are used, there is not the danger from disease organisms that there is from raw cream. An “aged” cream is to be desired for ice-cream-making because it is more viscous. By “aged” is meant the holding of the cream for a period after separating before it is made into ice-cream. Usually it is aged for twenty-four to thirty-six hours. While aging it must be kept cold so it will not sour and it should not be frozen. It is hard to melt frozen cream and it is liable to cause the ice-cream to be grainy.

The demand for ice-cream fluctuates with the weather changes. When it is hot there is an extensive demand but if the weather rapidly becomes cool this demand suddenly decreases or vice versa. This means that the ice-cream-maker either must carry or have at his disposal a variable supply of cream. When hot weather increases the demand, there may not be time to age the cream or it may be held so long that it becomes sour. Homogenized or emulsified cream is to be desired for ice-cream-making because it gives a smoother body and texture to the product. This is undoubtedly due to the fat globules and other solids being broken up into smaller particles by the process.

7. Why milk and cream are not of the desired quality.

—Some milk and cream has undesirable flavors which may be more or less pronounced. These are due to: the flavor of foods eaten by the cow; the absorption of flavors and odors from the atmosphere; the health of the cow; the bacteria present. If not properly handled, the milk and cream will soon become sour.

8. The flavor of foods eaten by the cow.

—The presence of undesirable flavors in the milk is due many times to the cows eating foods with very pronounced flavors. Most common of these foods are onion, garlic, turnips, cabbage, decayed ensilage, various pasture weeds, and the like. The flavoring oils are volatile and so are able to pass easily through all the tissues of the animal, and in a short time pass off through the various excretory channels. During the time that the food is undergoing digestion, these volatile oils are not only present in the milk, but all the tissues of the animal. By the time the process of digestion is completed, the volatile flavors will have passed away largely. Therefore, if the time of milking and feeding are properly regulated, a dairy-man may feed considerable quantities of strong-flavored food, without any appreciable effect on the flavor of the milk. To do this successfully, the cows should be fed immediately before or after milking, preferably the latter. This allows time for the digestive process to take place, during which time the volatile substances will have passed away. While, if the milking occurred three or four hours after feeding, these volatile substances would be present in the milk and so flavor it.

In the case of those plants which grow wild in the pasture and to which the cows have continued access, it is much more difficult to overcome the bad flavor in the milk. The only thing which can be done is to allow the cows to pasture for a short time immediately after milking. This will make it necessary to supplement the food of the pasture with dry feed, or to have another pasture where these undesirable plants do not grow.

9. The absorption of flavors and odors in the atmosphere.

—Milk, especially when warm, possesses a remarkable ability to absorb and retain odors in the surrounding atmosphere. For this reason, the milk should be exposed only in a surrounding of clean pure air. Some of the common sources of these undesirable odors are: bad smelling stables; unclean cows; aërating milk near hog pens, barnyards, swill barrels, and like odoriferous sources; strong-smelling feeds in the stable during milking, and the like. The only way to overcome these undesirable flavors and odors in the milk is not to expose the milk to them. The safest policy is to remove the source of the odor.

10. The unhealthy condition of the cow.

—Milk secreted just before or just after parturition is different in physical properties and chemical composition from that secreted at any other time during the lactation period. This milk is known as colostrum. It is considered unfit for human food, either as milk or products manufactured from the milk. Most states consider colostrum adulterated milk, and prohibit its sale fifteen days before or five days after parturition.⁠[3]

Whenever disease manifests itself in the cow, the milk should be discarded at once as human food. Some diseases are common both to the cow and man, such as tuberculosis and foot-and-mouth disease. If such diseases are present in the cow, the milk acts as a carrier for them to man. Digestive disorders of any sort in the cow are frequently accompanied by undesirable flavors in the milk. These are not believed to be due to the food eaten, but to the bad condition of the animal. On resuming a normal condition, these undesirable flavors disappear. This is especially noticeable when cows are turned out to pasture for the first time in the spring, or when they are pastured on rank fall feed, such as second-growth clover.

11. The bacteria in the milk.

—The bacteria are microscopic unicellular plants without chlorophyll. Besides bacteria, there are other forms of the lowest orders of the vegetable kingdom found in milk, such as yeasts and molds. The general characteristics of yeast and bacteria are somewhat similar. Bacteria are very widely distributed throughout nature. They are so small that they may float easily in the air or on particles of dust. They are so resistant to adverse conditions of growth that they may be present in a dormant or spore stage, and thereby not be recognized readily; when suitable environments for growth are again produced, germination takes place at once. They are found in all surface water, on the surface of the earth, and upon all organic matter. There are a great many different groups of bacteria, some beneficial and some harmful to man. As they are so small, it is difficult to differentiate between the beneficial and harmful groups, except by the results produced or by a careful study in an especially equipped laboratory. Bacteria have many forms, the three common forms being: spherical (coccus); rod-like or cylindrical (bacillus); and corkscrew (spirillum). The bacteria reproduce very rapidly by fission, that is, a transverse partition forms in the cell and when this partition is completed, the cell is divided. There are then two bacteria where there was but one before. In some cases, this division has taken place regularly in twenty to thirty minutes. Like other plants, they are very sensitive to a food supply, to temperature, and to moisture, as conditions of growth. Inasmuch as the bacteria are plant cells, they must imbibe their food from materials in solution. They may live on solid substances, but the food elements must be rendered soluble before they can be utilized. Bacteria prefer a neutral or slightly acid medium for growth, rather than an alkaline reaction; however, there are many exceptions to this. The food for bacteria must contain carbon, hydrogen, oxygen, and nitrogen, together with small amounts of mineral matters. Organic compounds make available food supplies. Ordinary milk furnishes a very favorable medium for the growth of bacteria because it contains an adequate and easily available food supply. In milk, there are certain groups of bacteria, which are ordinarily present, but any others which happen to get into the milk will live and rapidly multiply. Most forms of bacteria are dependent on temperature as a condition of growth. There is a range of temperature, more or less wide, at which the bacteria will grow and multiply with the greatest rapidity. This is called the optimum temperature and varies with the different groups of bacteria, but for most it is between 75° F. and 95° F. Growth of most of the bacteria found in milk will take place between 40° F.-45° F. to 105° F.-115° F. Above and below these temperatures growth is retarded, and, if carried to extremes, life will be destroyed. Like plants which form structures called seeds to carry them through conditions unfavorable to growth, so some groups of bacteria form spores. The spores are exceedingly resistant to unfavorable conditions of growth, such as heat, cold, drying, food supply, and even chemical agents. It is this property which makes it difficult to destroy some bacteria.

Because of the harmful effect of the micro-organisms in the milk and cream, precautions should be taken to keep them out. If they do enter, their growth can be checked by keeping the milk and cream cold. What has been said regarding bacteria is true of molds and yeasts.

12. The sediment test.

—The amount of solid material or dirt in the milk is an indication of the amount of bacterial contamination. It should be remembered that the strainer will take out the solid material, but the soluble portion and the bacteria will be left in the milk or cream. Thus an efficient strainer will defeat the sediment test. There are several sediment tests on the market. The test consists of filtering about a pint of milk through a cotton disc filter about an inch in diameter. The solid material or dirt is left on the filter. (Fig. 2.) The amount of dirt would indicate the amount of contamination in the milk. Much improvement in the quality of the milk has been accomplished by the use of the sediment test, because the cotton discs with the dirt are posted where each patron can see them and pride causes the careless dairy-man to take more pains in the care and handling of his milk.

13. How to prevent the growth of micro-organisms in the milk and cream.

—Next in importance to clean production in the care of milk and cream, is the prevention of growth or development of the organisms in it. This is accomplished by cooling and keeping the milk and cream cold and covered. If they are produced clean and kept covered, there are certain to be some micro-organisms in the milk and unless cooled these will develop and quickly spoil the milk and cream. Ross⁠[4] and McInerney give the following summary regarding the cooling of milk and cream:

“Milk becomes cool, of course, when it gives up its heat to some substance colder than itself, and in order to have a rapid exchange of temperatures between two substances it is necessary that they have approximately the same density. On account of the great difference in density between air and milk, the latter will cool very slowly in air even though the temperature of the air is rather low. If milk is allowed to cool by standing in a cold atmosphere, it will do so unevenly, and by the time the milk in the center of the can is cooled, that part near the walls of the can may be frozen. The fat is not evenly distributed in frozen milk; therefore it is not so good as normal milk.

“1. The bacteria-content of milk held at a temperature of 50° F. increases slowly, while the bacteria-content of milk held at 90° F. increases rapidly.

“2. At a temperature of 90° F. bacteria increase rapidly in milk that had either a small or a large amount of bacteria in it originally.

“3. Cooling milk by placing the cans in a tank of ice water is a practical method for use in farm dairies. To cool the milk rapidly it must be stirred at frequent intervals.

“4. Stirring the milk at intervals of five minutes caused a sufficiently rapid drop in temperature. Rapidity of cooling due to stirring the milk at intervals of five minutes and at intervals of ten minutes was very slight.

“5. When sufficient quantities of ice were used, stirring the water in the cooling tank had little effect on the rapidity of cooling.

“6. In order to obtain the best efficiency from the conical type of cooler, it is absolutely necessary to stir the water inside the cooler.

“7. Lower temperatures can be obtained by using brine and ice than with ice water alone.”

Stocking⁠[5] shows the effect of temperature on the development of the bacteria in milk by the following experiment: A sample of milk, which was thoroughly mixed, was divided into six equal parts. The six bottles were placed in water at different temperatures for twelve hours, at which time the germ-content of each lot was determined. The six bottles were then all placed together in a temperature of 70 degrees and allowed to remain until they curdled. As each sample curdled, the time was recorded. The difference in the germ-content and the keeping time is the result of the difference in temperature for a period of twelve hours only, and shows what may happen easily in milk which is allowed to stand overnight without thorough cooling.

Table I
Effect of different temperatures for twelve hours on the growth of bacteria and on the keeping quality of milk

14. Milk and cream production and handling.

—The following diagram shows the main sources of contamination and the undesirable methods of handling by which the quality of milk and cream is impaired:

Sources of contamination and undesirable methods of handling

The above shows that the producer controls most of the factors which concern the sources of initial contamination.⁠[6] After the milk leaves the producer, if it is not properly handled, the organisms in it may develop or if exposed to dirty conditions more contamination may take place. The important factors in the production and handling of milk are: clean utensils, clean healthy cows, small-top milk-pails, proper cooling and maintaining of low temperature, 50° F. or below. The importance of can jackets to aid in keeping the cream cold should not be overlooked, especially when shipping in hot weather. The quality of the milk and cream is largely determined by the time it is delivered at the ice-cream plant.

15. Clarifier.

—If solid or semi-solid dirt either visible or invisible is in the milk, it can be removed by the use of a clarifier. This is a specially devised machine (Figs. 3 and 4) which takes out the dirt by centrifugal force. It is desirable to clarify milk and cream for ice-cream-making. Besides removing dirt which gets into the milk during handling, the clarifier also takes out blood corpuscles and pus cells which are sometimes secreted with the milk.

16. The chemical composition of the milk and cream.

—It is not possible here to discuss in detail the composition of the milk and cream and the factors influencing it. Ross⁠[7] gives the composition of milk, cream and skimmed-milk as follows:

Table II
Showing composition of milk

Table III
Showing composition of cream

Table IV
Showing composition of skimmed-milk

From the view point of the ice-cream-maker, the fat and solids not fat are of special consideration. Each state has standards for milk, cream and skimmed-milk. (See Table XV.) The federal standards⁠[8] are as follows: Milk is the fresh clean, lacteal secretion obtained by the complete milking of one or more healthy cows, properly fed and kept, excluding that obtained within fifteen days before and ten days after calving and contains not less than eight and one-half (8.5) per cent of solids not fat and not less than three and one-quarter (3.25) per cent of milk-fat.

Skim-milk is milk from which a part or all of the cream has been removed, and contains not less than nine and one-quarter (9.25) per cent of milk solids. Cream is that portion of milk, rich in milk-fat, which rises to the surface of milk on standing, or is separated from it by centrifugal force, is fresh and clean and contains not less than eighteen (18) per cent of milk-fat.

Milk and cream should be purchased on the fat test and not by measure, the price being based on the fat-content. For method of testing, see Chapter XIV.

Because of the variable composition of milk and cream, it is necessary to standardize them for use in ice-cream-making. For method of standardization, see Chapter XIV.