The book of ice-cream

The principles of freezing are the same whether a large or small freezer is employed. It is usually harder to control the process in a small receptacle. In a large plant the freezers are arranged in a row or battery, as shown in Fig. 52. One man operates six to eight, with a helper to carry the ice-cream to the hardening-room.

108. Purpose of freezing.

—Freezing is for the purpose of cooling the mix and getting it in such condition that it is edible while frozen. If frozen without agitation it would be icy and grainy. If the mix is placed in the freezer too warm, it is liable to churn. Freezing incorporates air into the ice-cream and so gives pore space. The increase in volume due to freezing is known as “swell” or “over-run.”

109. Rate of freezing.

—If the freezing is not properly done, the result is a loss in both quality and quantity of ice-cream. The rate or time required to freeze is affected by different factors, depending on the type of machine used.

In the brine freezer, the rate is dependent on the following factors: 1. Temperature of brine; 2. rate of flow of brine; 3. temperature of materials when put into freezer; 4. materials in mix; 5. speed of the freezer.

In the tub and can freezer the rate is dependent on the factors: 1. Proportion of salt and ice; 2. amount of brine; 3. mixture of salt and ice and brine; 4. speed of freezer; 5. temperature of materials when put into freezer; 6. materials in mix.

Ice-cream should not be frozen too fast or too slowly nor for too long or short a period. If the extremes occur, the quality and quantity are affected.

Results of freezing too rapidly:

1. Cannot obtain swell.

2. Causes cream of poor quality.

1. Soggy or heavy—due to lack of air space.

2. Grainy in texture.

3. Does not hold well in storage.

Results of freezing too slowly:

1. Cream is liable to churn, causing chunks of butter in the ice-cream.

2. Greasy ice-cream.

3. Cannot obtain swell.

4. Ice-cream usually lumpy.

Results of not freezing enough:

1. Ice-cream is watery.

2. Ice crystals separate while hardening.

3. Do not obtain proper swell.

4. Fat rises to surface of the ice-cream.

Results of freezing too much or too long:

1. Liable to churn cream.

2. Lose swell.

3. Ice-cream is liable to be greasy.

4. Ice-cream is soggy and heavy.

The rate of freezing can be regulated much easier in the brine than in the tub and can freezer. In the former the condition of the ice-cream can be seen without stopping the machine, and also the temperature taken. On the other hand, with the tub and can freezer, the machine must be stopped each time and the cover removed in order to see the condition of the ice-cream or to take the temperature of it. With the brine freezer the rate of flow of the brine can be regulated. The temperature of the brine alone is not important, but the rate of flow must be considered. In the tub and can freezer the proportion of ice and salt can be regulated, but this is not very satisfactory. The ratio of salt to ice regulates the rate of freezing. (See page 108.) Usually one part salt to twelve to eighteen parts of ice is the correct proportion. The finer the ice and salt, the more rapid the freezing.

The rate of freezing is also affected by the amount of sugar and solids in the ice-cream. The effect of sugar on the temperature is shown in Table V.

Table V Effect of sugar on freezing

The effect of a large percentage of sugar on the freezing is especially noticeable in the case of sherbets and ices. These freeze much slower than ice-cream.

110. Proper method of freezing.

—The question might be asked as to the proper way to freeze ice-cream. Because of the many factors involved, the only direct answer is to state that the process should result in a mellow body, smooth texture and medium swell. The colder the mix when it enters the freezer, down to 40° F., the better the control. It should take from twelve to twenty minutes to freeze. The mix should be cooled quickly to 32° F., then the flow of brine partly shut off and the cream allowed to whip. When the cream is nearly whipped, the brine should be turned on gradually and the cream allowed to freeze. When the mix is partly frozen, the fruit should be added, soon enough so that there will be time for it to become uniformly distributed in the mix. It is the usual practice to crush the whole fruits before putting them in the freezer. This can easily be done by forcing them through a food chopper. The cream should come from the freezer at a temperature of 26° F.-28° F. The appearance of the ice-cream and its temperature is a good index when frozen enough. It should have its peculiar characteristic (dead) not shiny appearance. When the thermometer is placed in the freezer and drawn out, the ice-cream should adhere to it and the part remaining on the thermometer should retain its identity for a few minutes.

Experiments⁠[26] show that between 29° F. and 26° F., the volume of the ice-cream increases as the cream whips. The flow of brine, therefore, should be regulated so that the cream will be at the temperature at which it will whip, for the maximum of time. If the freezer is run with the mix too warm, the cream will churn, and if the mix is too cold, the cream will not whip.

In a tub and can freezer it is difficult to control the factors regulating the rate of freezing. When the mix begins to thicken and so turns hard, the speed of the freezer is increased. This beats up the ice-cream and causes more swell. When the dasher and ice-cream are removed, the freezing-can will float in the brine, causing considerable difficulty when the next mix is ready to be frozen, since it will not easily go back in place. If the freezing-can cannot be centered in the tub, the cold brine should not be wasted, but should be dipped out and poured back after the can is in place. This saves considerable ice. In many plants, no attempt is made to center the can in the brine, this being dipped out as soon as the ice-cream is removed.

One of the important factors in freezing is to obtain the proper swell. So far as this is concerned, the time to draw the ice-cream from the freezer can be told by the over-run tester. (See Chapter XIV.)

111. “Over-run” or “swell.”

—It should be the aim of the person freezing the ice-cream to obtain the proper over-run with each freezer. A large number of factors affect the amount of swell, and the possible combinations of these must be known. If too much swell is obtained, the ice-cream will be very porous, light and fluffy, and have a grainy texture; if not swell enough, it will be very heavy and soggy and may or may not be grainy in texture. For the best results, a medium swell is to be desired. The factors affecting swell⁠[27] may be divided into two general classes: kind and preparation of materials used, manner or method of freezing.

I. Kind and preparation of materials used.

 1. Age, viscosity, acidity, and fat-content of milk and cream.

 2. Size of fat globules in cream.

 3. Ageing of mix.

 4. Pasteurizing of milk and cream.

 5. Use of homogenizer.

 6. Use of emulsor.

 7. Methods of mixing.

 8. Use of condensed mix.

 9. Amount of sugar.

10. Different kinds of flavoring.

11. Fillers and binders.

12. Total solids in mix.

The older the milk and cream and the more acidity they contain, the more viscous they will be. This is to be desired since it will whip more readily. For test for viscosity, see Chapter XIV. The more fat present in the milk and cream the more viscous they will be and the smaller the fat globules, the more the cream and milk will whip. It is commonly known that in order to obtain viscosity and swell, aged cream must be secured. Instead of ageing the milk and cream, some manufacturers age the whole mix. If only the former are aged and these should sour, they could be churned into butter. However, if the sugar and flavoring are added to the mix and the whole aged and in the process become sour, the cream would not make good butter when churned. Therefore, there is danger of greater loss when the whole mix is aged. Pasteurization temporarily destroys the viscosity of the milk and cream and as a result pasteurized cream must be aged longer to restore the viscosity. The homogenizer and emulsor breaks the solids of the milk and cream into smaller particles. In some plants the whole mix is homogenized or emulsified before going to the freezer. This increases the viscosity and because of this and of the smaller particles, more swell is possible without sacrificing quality. With the emulsor, cream can be made from butter and skim-milk, but it lacks the force of the homogenizer, and so cannot break up the solids as can the latter. Emulsified cream is more viscous than raw cream of the same age.

While mixing, care should be exercised not to churn the cream. If churning takes place, it reduces the solids and so the possible swell. By the use of condensed or powdered milk, the amount of total solids in the mix is increased. Condensed milk usually causes the mix to become more viscous. The amount of sugar is important only because of its bulk; the more sugar added, the more solids in the ice-cream. The swell is affected by the flavoring since some flavors add more bulk.

Authorities disagree as to the effect of binders and fillers on swell. If some cause an increased swell, this is very slight. The total solids in the mix have a decided influence on the amount of swell that can be obtained without injury to the quality of the ice-cream; the more solids in the mix, the more swell.

II. Manner or method of freezing.

 1. Speed of dasher in freezer.

 2. Temperature of mix entering the freezer.

 3. Temperature of brine and rate of flow.

 4. Temperature of mix while whipping.

 5. Time of whipping.

 6. Total time to freeze.

 7. Temperature of ice-cream when drawn from freezer.

 8. The amount of mix in the freezer.

The manufacturers of the different freezers have studied their machines and determined the speed at which they should run. The ice-cream-maker should see that the freezer runs at the speed indicated.

The nearer the temperature of the mix to 40° F. when put into the freezer, the easier it is to obtain the swell.

Mortensen⁠[28] says “that a temperature of about 6° F. for the circulating brine would be the most desirable when using a 20 per cent raw cream. For pasteurized cream a temperature of from 8 to 10° F. gave the best results, while for emulsified cream about 10° F. and for homogenized cream 14° F. proved the most satisfactory.” No record of the rate of flow of brine is recorded. The temperature and flow of the brine should be such that the desired swell is obtained together with the quality.

Washburn⁠[29] shows that the mix whips at certain temperatures, usually from 32° F. to 29° F. The length of time of whipping has a decided influence on the quality of the ice-cream and the amount of swell.

The total time to freeze has a noticeable effect on the quality of the ice-cream and the amount of swell. If frozen too quickly, swell will not be obtained and if too long, swell will be lost.

Washburn⁠[30] proves that the temperature at which the ice-cream is drawn from the freezer has a marked effect on the swell. If frozen too cold, the swell is lost.

According to Mortensen⁠[31] the amount of mix in the freezer influences the swell. For the best results, the freezer should be about half full.

Certain combinations of the factors mentioned above will increase the swell, while certain ones will decrease it.

To obtain swell:

 1. Have viscous milk and cream.

 2. Age the milk and cream or mix.

 3. If pasteurized milk and cream are used, they should be aged until viscous.

 4. The cream and milk or whole mix should be homogenized or emulsified.

 5. Condensed milk in the mix would aid in obtaining swell.

 6. The mix should contain at least 30 per cent of total solids.

 7. The dasher should run at the required speed.

 8. Mix should enter freezer as near 40° F. as possible.

 9. There should be a supply of cold brine, from 6° F. to 10° F.

10. The cream should be whipped for a moderate time in the freezer.

11. The mix should fill the freezer half full.

12. It should require 12-20 minutes to freeze.

13. The ice-cream should not be below 27° F. when drawn from the freezer.

The converse of these conditions will cause a decrease in the amount of swell.

112. Condition of ice-cream when removed from freezer.

—When taken from the freezer, the ice-cream is in a semi-solid condition. It is soft enough to flow from one container to another and yet hard enough to retain the incorporated air. In order to use the freezer over and over, the ice-cream is usually placed in pack-cans to harden. A parchment paper is put over the top of the can before going to hardening-room. The ice-cream can be drawn from brine freezers directly into the pack-cans. With the tub and can ice freezers, it is necessary to dip the ice-cream from the freezer into the pack-cans. This is more easily done if the dasher is first removed.

113. Freezing sherbets and ices.

—The foregoing statements apply to ice-cream and may or may not be applicable to sherbets and ices. Because of the higher percentage of sugar and water, the latter usually freeze more slowly. Any difference in procedure is noted under the receipt for sherbets and ices.