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Ice Cream Technology

( Originally Published 1939 )

Permit. Just as in milk-plant operation, a prospective ice-cream dealer must apply to the official control agency, usually the health department, for a permit to operate (see pages 58, 128). State laws and regulations for ice-cream control are usually administered by the agriculture and health departments.

Preparation of mix. Although the proximate analysis of ice cream would indicate that its manufacture is a simple operation of measuring butterfat, sugar, and condensed skim milk, the actual commercial procedure is far more complicated. Butterfat is not available as such. It is used in the form of cream, usually of about 40 percent butterfat content, and whole milk. Sugar is easily weighed out directly, but if sweetened condensed milk is used, allowance must be made for the sugar it contains. The solids-not-fat is made up from the non-fat portion of the cream, from the condensed skim milk, and from the whole milk.

One of the desirable properties of ice cream is a fine, smooth texture. This is obtained partially by the use of ingredients which hold the water in a hydrated form, thereby facilitating the formation of small ice crystals. Protective colloids have been found to be effective in this respect. These are high-grade gelatin, vegetable gums, fruit pectin, sodium alginate from kelp, and various products from milk casein. Sometimes a small amount of eggs is added to improve the whipping properties of the mix.

It has become common practice to add color to some mixes, de-pending on the local demand. This is particularly true of the fruit ice creams, and also the ices and sherbets.

All the liquid ingredients are put into a vat and heated. This vat must be provided with sanitary fittings and an agitator.

Pasteurization. After the liquid ingredients have been well mixed and heated, the dry ingredients are added. These may be the sugar, stabilizer, eggs, chocolate, color, and other materials. While they are all being stirred together, the heating is continued until the pasteurizing temperature is reached, which is maintained for 30 minutes to pasteurize all the ingredients. Ordinarily a pasteurization temperature of 150° F. is used. This helps to dissolve the ingredients as well as to kill all pathogenic organisms. Fabin and Coulter showed 2 that the strains of the Escherichia-Aerobacter group survived experimental pasteurization temperatures of 65.°5 C. (150° F.) for 30 minutes, and that they required a temperature of 68.°3 C. (155° F.) for destruction. In those localities where regulatory officials require that ice cream be free from these organisms, ice-cream dealers pasteurize their mix at temperatures of 160° F. or higher.

Homogenization. One of the factors which contributes largely to the smoothness of ice cream is the fineness of the subdivision and the degree of dispersion of the butterfat globules. If these globules are large, the ice cream may be coarse. In order to break these down, a machine called a homogenizer, or a viscolizer, is used. In principle, this is a powerful pump which forces the liquid through very small orifices. The pressures may run up to 4000 pounds per square inch. The specific action of the valve to break up the globules is not clearly understood. The average diameter of a butterfat globule in milk or cream may be about 3 to 8 microns (1 micron is 1/25,000 inch) ; after homogenization, it is about 1 to 2 microns.

This treatment has the further advantage that it contributes to a more effective mixing of the ingredients by disintegrating any other small soft materials. Its performance is literally to make the product homogeneous. Homogenizing at pasteurization temperatures gives the best quality of mix from the standpoints of good whipping proper-ties in the freezer and of maintaining temperatures which prevent the growth of all harmful bacteria.

Cooling and aging. After the mix has been homogenized, it is cooled to about 35° F. by equipment similar to milk coolers, and is then pumped to storage tanks to await freezing. Sometimes the mix is held under refrigeration for 24 hours, more or less, to impart properties which have been considered to be helpful to improve the whip-ping of the mix in the freezer and the resultant texture of the ice cream. This treatment has been called "aging." It is doubtful whether any practical advantage is obtained by aging for much longer than 4 hours.

Freezing. Ice-cream mix is frozen in single-batch machines or in continuous freezers. In general, both machines utilize a cylindrical chamber with double wall which acts as a jacket to contain the refrigerant. On the axis of the cylinder, a rotating dasher and scraper keep the mix thoroughly agitated and remove the ice from the refrigerated walls.

In the batch type, a charge of mix about half fills the machine. The brine (refrigerant) is then turned on, and the dasher and scraper started. In about 5 to 10 minutes the operation is completed, and the batch is discharged by opening a gate in the front of the freezer. The mix has been chilled to a temperature of about 23° F. and has in-creased greatly in volume by virtue of the whipping motion of the dasher blades, giving it the consistency of whipped cream. It is drawn off quickly into the containers, and rushed into the hardening room. Flavors, fruits, and nuts are added to the batch in the freezer just before it is drawn.

In the continuous freezer, a mixture of the ice-cream mix and a controlled volume of air is pumped under pressure into one or more horizontal jacketed tubes, each provided with a rotating dasher and scraper. The mix is chilled to a temperature of about 21° F. and is slowly and continuously forced out of a vertical discharge tube directly into the final containers. These are then placed in the hardening room like the ice cream from the batch freezers.

Overrun. While the mix is being violently agitated in the freezer to produce uniform freezing, the air is incorporated by the whipping action of the dasher. The increase in the volume of the mix is known as the swell or overrun. Practical considerations of palatability of product limit the extent of this to an increase of 75-100 percent over the original volume of the mix.

This overrun is just as essential to a satisfactory ice cream as leavening is to bread. Both would be unsaleable without the "lightness" that is obtained by thoroughly incorporating air and gas respectively in the mix and dough. If ice cream were frozen with little or no air, it would be excessively cold in the mouth, coarse and soggy in texture, and lacking in that quality of creaminess and smoothness which is one of its main attractions. On the other hand, too great an overrun would make the ice cream frothy.

Hardening. Although the ice-cream mix has been chilled in the freezer to temperatures of about 21-25° F., it does not become homogeneously and immediately frozen hard. The mix contains so many substances with varying freezing points of their saturated solutions (called cryohydric points) that the complete freezing of a mix would occur somewhere below -67° F. Therefore, the refrigeration must be continued until enough ice has been formed to make the mass hard. The thick, creamy mixture from the freezers is placed in hardening rooms which are held at temperatures of about 0 to -30° F. where the "freezing" is completed to the extent of producing the plastic mass which constitutes ice cream.

Packaging. Although most of the ice cream is sold in bulk for the fountain trade, large quantities are now being packaged in quart and pint sizes in containers packed at the factory. Machinery has been developed so that the ice cream products pass from the original mixing vats to the final wrapped package without coming in contact with human hands. Such ice cream is as sanitary as a bottle of certified or pasteurized milk.

Operation of plant. Ice-cream plants operate under as exacting sanitary standards as those that obtain for milk plants. The employees are medically examined, the raw materials come from inspected sources, the products are pasteurized with the precision of milk handling, and the plant is built for effective cleaning and with adequate light and ventilation. After every day's run, all the equipment is flushed out with water, then dismantled, scrubbed with an alkaline cleansing agent, and finally sterilized with scalding water or a chlorine solution, or both. The industry itself has published 4 de-tailed instructions for the guidance of ice-cream dealers in keeping their plants sanitary. Some of the machinery is so much more intricate than any used in the milk industry that special means must be employed to clean and sterilize it as, for example, the homogenizer, the specialty machines, and particularly the freezer.


Flavored ice cream. The great bulk of ice cream is flavored with vanilla. Usually this is in the form of an extract. Some markets require a highly flavored product, and therefore synthetics may be used. No health problem is involved in their use because these products are chemically the same as those occurring in the natural ones. The so-called Philadelphia ice cream is flavored with ground vanilla beans which appear as fine dark specks throughout the mass.

Chocolate ice cream may be flavored with liquor chocolate or cocoa. The liquor contains much more cocoa butter than cocoa does; therefore a larger amount of liquor chocolate is required to give a flavor equal to that of a smaller amount of cocoa. This makes a richer product than may be desired. There is a belief that chocolate ice cream is made of the reruns from returns of miscellaneous flavors which are melted down together and made into chocolate ice cream to cover up the mixed origin. This absurdity persists because people do not realize that competition to produce a palatable chocolate ice cream is just as keen as that to produce any other flavor, and that if a dealer resorted to such practices, he could not survive. A good chocolate ice cream is a market favorite. Although a small amount may be made by adding the chocolate at the freezer, by far the greater part of it is made by adding the chocolate to the mix, and then pasteurizing the whole batch.

Another very popular flavor is strawberry. Canned strawberries do not give as good flavor as the fresh or cold-packed berries. Great care is necessary in the handling of the dairy products used in strawberry ice cream to prevent contamination with the copper of the equipment, because traces of copper have a tendency to impart an off-flavor.

Other popular flavors are banana, pineapple, peach, orange, and raspberry. Nuts may be used, with or without other added flavor ingredients, such as burnt almond, black walnut, maple-walnut, buttered pecan, or pistachio.

Usually a small amount of prepared color is added to supplement that of the fruit or nuts. This gives a uniformly colored product which would be difficult to obtain if the manufacturer had to depend on the varying shades of successive lots of fruit. Furthermore, the public has learned to associate certain colors with certain flavored ice creams, thereby giving the practice the sanction of custom. Every batch of pigment is examined by the U. S. Department of Agriculture for freedom from harmful ingredients, and is given a lot number for identification. The only ones that are used are those officially certified to be harmless.

Layer-brick ice cream is made by running the chilled mix from the freezer into a tray about 27/8 by 61/4 by 26 inches to about one-third full, leveling it off and hard-freezing it in the hardening room. The tray is then brought out, and another flavor run in to about two-thirds full. After this has hardened, a last flavor is added, and the tray is again returned to the hardening room. To remove the ice cream, the tray is dipped in warm water to loosen the three-layer slab, and then is inverted on a table so that, when a blast of air is applied to one or more vent holes on the bottom, the slab is forced out. This is then cut crosswise into bricks, and wrapped for packaging. Layer-brick ice cream usually has a lower overrun than bulk ice cream because allowance does not have to be made for the dipping pressure of the dispenser. Layer-brick ice cream may also be made by special package-filling machines, directly from the freezer.

There are several varieties of frozen dairy products which are distinguished by their difference in composition, fat, and sometimes egg content. Bisque ice cream may contain bakery products. A mousse is richer in fat than plain ice cream. A parfait contains eggs. A pudding contains more butterfat and a greater amount of fruits than ice cream. Frozen custard is always lower in butterfat than ice cream, and is made on a custard base. A new product recently introduced is called ice milk because of its low butterfat content. This product has a composition as follows:


Fat 4— 41

Milk-solids-not-fat 11—15 (mostly 14—15)

Sugar 13—15

Stabilizer 0.2—0.6

The low fat percentage makes possible an increase in the other milk solids so that the total solids approach those of regular ice cream without the crystallization of lactose. This higher proportion of non-fat solids to fat gives a nutritive ratio more closely approaching that of milk than regular commercial ice cream. Sherbets are made of milk, fruit juice, and sugar, with color added, and also citric or lactic acid to give tartness. If egg yolk is an ingredient, the sherbet is called a soufflé. If no milk is used, the product is an ice.

These ices have appeared on the market under a number of trade names such as Popsicle, Fudgicle, and Creamsicle. Often they are sold on sticks which serve as handles, and are eaten like candy lollipops. Ice cream may be coated with chocolate and sold for eating on sticks likewise.

Sommer has written an excellent treatise on the manufacture of ice cream and its many problems.' See also the paper by Fabian,

"What are frozen desserts?"

Market outlet. Ice cream was developed originally as a confection or dessert. In the last twenty years or so, the per capita consumption has about tripled. The application of the most modern sanitation methods, together with the discovery of the unique value of dairy products in human nutrition, has led the industry to develop a market for ice cream as a food as well as a dessert. This finds in-creasing emphasis in the use of ice cream by children, by convalescents, and in hospitals, as well as by the public at large.


Nutritional value. Ice-cream mix consists so predominantly of concentrated dairy products that it possesses a nutritional value superior to that of an equal weight of rich milk. This can be readily appreciated from a study of the typical composition 8 as shown in Table VI. Ice cream made from this mix would have a content of milk solids of about 22 percent, and a content of total solids of about 39 percent. Pure milk contains about 4 percent butterfat and 8.5 percent solids-not-fat, making a total milk solids content of about 12.5 percent. When fruits are added to ice-cream mix, there is a proportionate dilution of this basic "white" mix. In some brands, a small amount of harmless coloring material (certified colors) is added. Also, many brands add about 1/3 of 1 percent of a protein or vegetable product called a "stabilizer," in order to impart smoothness and fine texture to the finished ice cream.

Many persons believe that commercial ice cream contains "fillers." By this they mean that the quality is lowered by the addition of a large amount of a cheap ingredient, such as cornstarch, and some include gelatin in this category. Commercial ice cream never contains any cornstarch or any other filler. In the first place, this is illegal. Any manufacturer who might want to use a filler would lay himself open to prosecution by the food-control officials and would probably lose trade because of the inferior palatability of his product. Gelatin is the most expensive ingredient in ice cream (when used at all). It costs more per pound than the butterfat, and accordingly no manufacturer uses any more than he absolutely needs for securing those properties of texture which he features in his own particular brand. All stabilizers, whether of vegetable or animal origin, are limited by law to a content of about 0.5 percent, and also by the fact that a slight excess over this maximum imparts a gumminess to the ice cream which renders its unpalatable. Therefore, it is clear that there is no conscienceless dilution of the legitimate ingredients.

From the above typical composition, it is seen that, on the weight basis, ice cream contains about three times the amount of nutrients that are in milk. On the volume basis, these relations do not obtain because the overrun property imparts a "swell" to the mix whereby 1 volume of mix usually becomes 1.8 volumes of ice cream. In Table VII is presented a calculation of the calorific value, the protein value, and the total food solids, respectively, of ice cream and milk, on the volume basis.

An average generous serving of ice cream contains about 51/3 fluid ounces which weighs 31/2 avoirdupois ounces (about three servings to 1 pint). An average ice cream cone may contain about 2 fluid ounces of ice cream, which has a calorific value of about 70 calories. This is about 1/35 to 1/50 of the heat energy required for the daily life of an average person.

The nutrient value of ice cream is enriched further by its content of the vitamins and minerals. Vitamin A is present in proportion to the relative content of butterfat, and accordingly ice cream is several times richer in this respect than milk. Vitamins B and G are present in the milk-solids-not-fat fraction of ice cream, about equal to their content in milk. There is only a negligible amount of the vitamins C and D in dairy products. The mineral content of ice cream resides in its milk-solids-not-fat; it is substantially as rich in these nutrients as milk.

Dietary importance. Almost every person likes the taste of ice cream. It has usually been eaten as a delicacy or as a dessert. However, many persons do not eat it for fear that it is fattening. They seem to think that it has some specific property which enhances the propensity to put on fat. Naturally, ice cream cannot possibly be any more fattening than its content of carbohydrate and fat. Its composition, shown above, indicates that this is not great in comparison with some other foods. In fact, a so-called reducing diet has been based on two helpings of ice cream each day, together with other foods such as certain amounts of meat, eggs, and fruit.

Some individuals do not drink milk because they dislike its flavor. Others claim that it "disagrees" with them. These objections do not, in general, apply to ice cream. Ice cream supplies all the nutritive elements which medical research has shown to be present in milk, and therefore it is admirably adapted as a constituent of the diet of those persons who cannot take milk. Many persons need their appetites to be stimulated by a pleasant and palatable food. Hospitals serve ice cream to patients and convalescents. Palmer ' has shown by experiments on rats that ice cream has a unique nutritional value. Several other investigations are reported 10 in which ice cream was fed to laboratory animals and children, and shown to possess excellent nutritive qualities for growth. Kramer and associates showed ' that the calcium and phosphorus in ice cream were utilized as well as those of raw milk.

There is a general belief that ice cream should not be eaten soon after the consumption of sea food. As a writer in the Journal of the American Medical Association, July 13, 1935, points out, there is no more reason for such an idea than that cream should not be eaten with cherries or meats with starches. Such a belief is possibly based on the unfounded ideas of the alleged incongruity of these products, but it may have behind it a remembrance of some unfortunate experience in the past when a near-spoiled product was used, and when sanitary control and refrigeration facilities had not been supplied with present-day effectiveness.

Cultural properties of mix. Mix consists so predominantly of milk and cream that it is similar in biochemical properties to these products, and, accordingly, it has all the food elements that are necessary for the growth of bacteria. Therefore, microorganisms proliferate about as readily in mix as they do in milk or cream. For example, mix can sour by bacterial growth just like milk. Mix must be pasteurized, refrigerated, and otherwise handled with all the sanitary care that is bestowed on milk to prevent its spoilage and deterioration.

Sources of infection. Ice cream provides more avenues of bacterial infection in its manufacture and distribution than other dairy products.

Usually the condensed milk and cream have been pasteurized before they are brought into the ice-cream plant. The fresh milk itself is frequently pasteurized in the ice-cream plant. The sugar usually is bacteriologically clean although until recently it often carried thermally resistant organisms. The gelatin stabilizers formerly carried very high bacterial counts, but improvements in gelatin technology have reduced these.

The coloring materials have been shown by Tracy and Prucha, Fabian, and other investigators to carry high yeast, mold, and bacterial counts, running into the millions per milliliter, and many were of human origin. Also, the nuts used in certain varieties of ice cream have been handled under conditions which were not always as sanitary as they should have been. The fruits and other flavors may likewise introduce their flora. See papers in J. Milk Technol., 2, 118 and 127 (1939).

Great care must be exercised to prevent contamination at the freezer where the flavors and fruits are added. After the mix has been pasteurized, it may be exposed to contamination by human contacts at numerous other places along the line. This requires that all employees must be free from infectious diseases. In addition, the employees must practice excellent personal hygiene to protect the mix from insanitary handling, even though the bacteria count might not be measurably increased thereby.

Ice-cream-plant equipment subjects the pasteurized mix to all the treatment given pasteurized milk, and in addition homogenizes it and whips it in the freezer. Both these latter operations break up any clumps of organisms that may be present, and also add the organisms which may be residual in this equipment itself. Fabian showed that there was no appreciable increase in bacterial count from the air whipped into the mix.

It is possible to maintain a plant in such excellent sanitary condition and to use such high-grade products that the accumulation of microorganisms throughout the manufacturing process can be kept to a negligible minimum.

In spite of all the great sanitary care given the manufacture of ice cream in the plants, it is possible to contaminate it by the grossly unsanitary conditions which often obtain in its retail dispensing. The type of help is often unacquainted with hygienic requirements. It is a common sight to see the ice-cream scoop left in a vessel with dirty water which has been found to contain great numbers of bacteria." Also the other dispensing equipment may be unclean. The vendor may contaminate the bulk ice cream in the cans with his fingers. Sometimes the top is left off the cans with attendant warming of the product and exposure to whatever contamination is at hand.

Fay investigated the bacterial counts of sherbets and reported that only 2 out of 21 samples of orange sherbets contained more than 100,000 bacteria per gram and only 5 contained more than 25,000, indicating that milk ingredients are the most important sources of bacteria in frozen desserts, and that the bacterial counts on water sherbets are useful for the detection of insanitary plant methods, especially improperly washed equipment.

Bacteria not destroyed by freezing. The freezing storage of ice cream has been shown by laboratory experiments to be no absolute protection against the presence of pathogenic organisms. Wallace and Crouch 15 quote the work of Davis, which showed that streptococci added to ice cream decreased only slightly in number over a period of 18 days, and did not decrease in virulence at all. Mitchell 18 inoculated E. typhosa into six batches of ice-cream mix made from cookbook recipes and stored the samples at -3° to -4° C. (24.8-26.6° F.). The whey separated from the creamy layer after several days. The organisms were found to survive for 12 to 39 days. Bolten inoculated samples of pasteurized ice cream with Eberthella typhosa and Corynebacterium diphtheriae (also known as Bacillus diphtheriae). Samples were removed at regular intervals and examined. On the seventy-fourth day, 2 tubes were weakly atypically positive and 2 tubes were negative. The diphtheria samples were frozen for 4 days and then inoculated into guinea pigs. All the pigs died, as did those inoculated with the unfrozen original cultures. No tests were made as to whether the organisms survived longer than 4 days.

Prucha and Brannon 18 inoculated E. typhosa into sterilized mixes of 12 percent sugar, 12 percent solids-not-fat, and 10 percent fat. They were incubated until the E. typhosa count was 25,000,000 per milliliter, then frozen, and stored in the hardening room at -8° to +8°, usually -4° F. (—20° C.). There was a rapid decrease in count in the first week, but this slowed down and was positive but dropping all the time until the tests were concluded after 2 years.

The organism Brucella abortus has been isolated by Fitch and Bishop 19 from ice cream prepared from cream known to be naturally infected. Wallace and Crouch inoculated commercial ice cream with a number of different kinds of pathogenic organisms, placed the samples in vials, and froze them at -23.2° C. (—10° F.). Vials were removed at regular intervals, and the contents were examined for viable organisms by plating on special media and by guinea-pig inoculation. They conclude that Salmonella enteritidis, S. aertrycke, Br. abortus, Br. suis, Br. melitensis, Mycobacterium tuberculosis var. hominis (Strains A, I, and S), M. tuberculosis var. bovis, and Mycobacterium avium survived freezing in ice cream for periods longer than 30 months, and point out that ice cream should not be considered a safe food merely because it is frozen. Wallace later reported 20 that none of these strains died off before 4 years, and some were still viable in the ice cream after storage at -23.3° C. (—10° F.) for 7 years.

Epidemiology. Numerous epidemics of disease have been directly traced to the consumption of ice cream. Fabian 21 has collected an imposing list of such outbreaks. Some additional ones are reported by Armstrong and Parran. The following list is compiled from the data furnished by these several investigators:

Typhoid fever 40 epidemics

Scarlet fever 2 epidemics

Diphtheria 1 epidemic

Septic sore throat 2 epidemics

Gastroenteritis 8 epidemics

Of these, 34 typhoid outbreaks involved 4342 cases, 1 scarlet-fever outbreak involved 128 cases, the diphtheria epidemic involved 402 cases, the 2 septic-sore-throat epidemics caused 385 cases, and 3 of the "food-poisoning" outbreaks involved 137 cases, a total of 5394 persons made ill by eating infected ice cream.

Hamilton 23 sent a questionnaire to many cities throughout the United States, of which 91 replied that 7 had experienced epidemics and 5 food poisonings from eating ice cream. Of the cities reporting, more than one-sixth had had trouble with ice cream. Geiger and associates report one very recent outbreak 24 in which several recurrences of typical food poisoning on shipboard pointed to ice cream as the cause. Careful investigation failed to identify the actual cause, but laboratory studies revealed very high bacterial colony counts of the epidemiologically incriminated nut ice cream. The correction of certain undesirable practices and the use of ice cream from shoreside sources of known sanitary quality resulted in no recurrence of food poisoning on this vessel.

There are doubtless many outbreaks which are not published, as evidenced by the one in Washington, D. C., in January, 1934, in which 386 persons were made ill in 4 to 12 hours after eating the ice cream.

The epidemiological investigation was quite unusual among food-poisoning outbreaks because of the definiteness of its findings. Each food that was eaten at the meal was examined. S. enteritidis was isolated from the ice cream and from the stools of numerous patients. Unfortunately, the source of the infection was not found in spite of the fact that the stools of the kitchen help were examined for the Salmonella group.


Standards and regulations. Recommendations of commission. The Commission on Milk Standards has studied the problems concerned in the sanitary production of ice cream 25 It considers that ice cream should be looked upon as a food rather than a confection. All the milk and cream used in the manufacture of ice cream should con-form to the requirements for milk and cream as such, and should certainly be pasteurized. Its definition of ice cream is representative of general practice:

Ice cream is a frozen product made from pasteurized cream and sugar, or pasteurized cream and pasteurized milk and sugar, and shall contain not less than 8 percent milk fat. It shall not contain any preservatives, neutralizing agent, saccharine, renovated or process butter, fats, or oils foreign to milk or to other ingredients allowed. It may contain wholesome eggs, harmless coloring matter, flavoring, sound, clean, mature fruits and nuts, pastries, and approved thickening not to exceed 0.5 percent.

The Commission urged strict sanitary control and recommended that the manufacture of ice cream be restricted to the products of the Grade

A and B classes, and that Grade A ice cream should contain no more than 100,000 bacteria per milliliter and that Grade B ice cream should contain no more than 1,000,000 bacteria per milliliter. The industry has now gone further whereby 100,000 is the maximum bacteria count recognized in most standards, and all the best plants produce ice cream well below this figure. This idea of grading of ice cream into A and

B grades has been incorporated in a Frozen Desserts Ordinance by the Department of Health of Memphis, Tenn., and by the new Frozen Desserts Ordinance and Code of the U. S. Public Health Service [J. Milk Tech., 1 (7), 33 (1938)].

Compliance with sanitary standards. Health of employees. Inasmuch as ice cream is predominantly a dairy product, it has been found necessary to require the same procedure for the examination of the plant employees as obtains for the milk industry (see page 129).

Sanitation. Usually the same standards of plant sanitation are required for ice cream as for milk, although it is not customary to find them so effectively enforced. In many communities, the industry itself applies a higher sanitary standard than the official requirements stipulate. Fabian states that in 1929 only 2 states and 1 province required pasteurization of the mix, whereas in 1935 there were 26 states and provinces requiring pasteurization of the mix or the milk products used.

Pasteurization. Ice-cream mix must be pasteurized for the same reasons that obtain for milk pasteurization. Inasmuch as mix contains about 36-40 percent total solids of which about 12-14 percent is butterfat, it is believed that a higher temperature of pasteurization is necessary than that required for the effective treatment of milk. A careful study of this was made by Oldenbusch, Frobisher, and Shrader, who inoculated cream with 2 strains of E. typhosa, 2 strains of beta hemolytic streptococci (1 from scarlet fever and 1 from septic sore throat), and 1 culture of bovine tubercle bacilli, and who also inoculated ice-cream mix with E. typhosa, 2 strains of hemolytic streptococci, and tubercle bacilli. They found that heating at 143-145° F. for 30 minutes allows an ample margin of safety for the pasteurization of cream and ice cream mix. They recommend a temperature of 145° F. for 30 minutes. Dubois and Martin 28 have studied the effect of pasteurization on the flora of mix, and find that in mixes made from raw dairy products, the flora after pasteurization was about evenly divided between the peptonizing and alkali-forming and the inert groups, whereas in mixes made from pasteurized ingredients the flora after pasteurization consisted largely of slow acid-formers.

Some communities require that ice cream must be free from Escherichia coli, and, in order to accomplish this, many plants pasteurize their mix at 155° or 160° F. for 30 minutes. Pasteurization at 150° F. is necessary to give a negative phosphatase test (see Reference 39, Caulfield and Martin).

Although it is almost a universal requirement in milk operations that the milk be pasteurized at the plant where it is bottled to prevent contamination during transportation, this protection is greatly neglected in ice-cream regulations. Only two cities, namely, Birmingham, Ala., and Baltimore, Md., have been found to require that mix be pasteurized at the plant where it is to be frozen. A serious typhoid epidemic in Birmingham led health officials to adopt this regulation for all ice cream sold there long before they required milk to be pasteurized at the bottling plant. We pay high for our experience.

Compliance with product standards. Almost all ice-cream standards require that ice cream must contain at least 8-14 percent butter-fat in plain ice cream, and about 2 percent less for fruit and nut ice cream (on account of the dilution of the mix which results from the addition of such flavoring materials). Most states specify 10 percent and 8 percent respectively. Several states require a minimum weight of 4.25 pounds, or 1.6 pounds food solids, per gallon of ice cream.

About one-third of the states have a standard for the content of total solids, varying from a minimum of 10 percent milk-solids-not-fat to 33 percent total solids.

Many states specify a maximum amount of stabilizer. This varies all the way from 0.2 to 1.0 percent, although most of these specify 0.5 percent. The rest of the states permit the use of a stabilizer but they have no stipulation as to the amount.

All fruits, nuts, and flavors must be clean, sound, wholesome, and handled in a sanitary manner.

Coloring materials are regularly permitted. If they are made from coal-tar dyes, they must derive from a list which is certified by the U. S. Department of Agriculture to have been examined and found to be free from any product which would have a harmful effect on the health of the consumer.

Some states and municipalities have set bacterial standards for ice cream. A maximum bacteria count by the standard plate technic of 100,000 organisms per gram of ice cream has been shown by Fay and Olson 29 and also by Fabian and Cromley and Fabian to be practical. However, it is well known that such a standard is very liberal because many plants produce regularly ice cream with counts under 10,000 organisms per gram. In the city of Baltimore, the average bacteria count of the ice cream of all large dealers in 1932 was 6400 and of the retail manufacturers 23,000. In the hot month of July, 1933, the counts averaged 8800 and 57,000 for the respective groups.

For full discussion of the composition of the various kinds of ice cream and other frozen desserts, together with official standards both chemical and bacteriological, see the paper by Fabian in the Journal of Milk Technology, 2, 75 (1939).

Types of adulteration encountered. Ice cream may be illegal by having a butterfat content or the percentage of solids below the legal standard for the particular product. The bacteria standard plate count may be in excess of the standard allowed. The content of colon organisms may be high. Some other fat may be used instead of butterfat. An excessive overrun may cause the contents of a package to weigh too little for the local standards. The product may have been packed under insanitary conditions, or in violation of the requirements of the health department or other regulatory organization.

Examination for adulteration and unwholesomeness. Physical examination. The ice cream should have a creamy consistency, and should be free from sandiness (lactose crystals) and ice crystals. Too much overrun imparts too frothy a body, whereas insufficient overrun makes the ice cream soggy, heavy, and unpalatable.

Microscopic examination of the mix will reveal whether the homogenizer has operated effectively.

Sediment in ice cream is determined by filtering onto a circular lintine disc, and comparing the degree of collected extraneous material with a standard.

Chemical examination. It is very difficult to secure a truly representative sample of ice cream because it is a mixture of two or more insoluble constituents. The weighing of a sample may be affected by the condensation of atmospheric moisture. Ormond has shown how to correct both of these.

Samples of melted fruit or nut ice cream cannot be pipetted without plugging, unless special precautions are taken. The best procedure is to macerate these solids with a stiff spatula in the original melted mixture, and then measure the sample for analysis with a pipette which has a wide orifice.

Butterfat. The official Roese-Gottlieb method of extraction is similar to the procedure for milk, but with slight modifications. The need for a quicker, more convenient procedure led to the development of the Mojonnier method, which is based on the Roese-Gottlieb method and utilizes a convenient arrangement of apparatus; it is almost universally used in ice-cream-plant control operations. The well-known Babcock method, so widely used for the determination of butterfat in milk, has been adapted with several modifications for ice cream. None of these methods, however, has proved itself.

Total solids. A sample of 1 gram is dried to constant weight by heating on a boiling water bath, and weighing. By the Mojonnier method, the sample is heated on a hot plate at 180° C. until the residue turns a light brown, then it is heated under not less than 20 inches of vacuum at 100° C. for 10 minutes, cooled in a desiccator, and weighed.

Acidity. To determine the acidity, 18 grams of sample are weighed into a white cup, twice the volume of distilled water is added, and the solution is titrated with 0.1 N sodium hydroxide, using phenolphthalein as indicator.

Foreign fats. The stress of competition keeps alive the idea of substituting a cheaper vegetable fat for the more expensive butterfat. To identify the fat, it is extracted from the ice cream in pure condition, and its chemical and physical properties are determined as out-lined in the official methods.

Colors. Ice cream should be examined to ascertain whether the colors used are the harmless ones certified by the If. S. Department of Agriculture. The methods used depend on the solvent extraction of the water- or oil-soluble colors from the treated mix, and their identification by color reactions with different reagents.

Phosphatase test. A properly pasteurized mix should show no phosphatase activity. Each flavor should be tested individually, with the nuts and fruits strained out. It is important that control tests be made to determine the presence of any reacting products from the flavors.

Bacteriological examination. Samples of the ingredients, after mixing with a sterile spatula, are placed in sterile bottles. Frozen ice cream is sampled by removing a portion, including the top layer, with a sterile spoon. Samples must be kept well refrigerated, and should be analyzed within 4 hours. The ice cream is melted at a temperature not to exceed about 110° F. to avoid injuring any of the organisms. Fay recommended 42 that, for routine testing, the volumetric measurement of the melted ice cream is sufficiently accurate, whereas for research or regulatory control, the gravimetric method is preferred.

Bacterial counts. The technic for making bacteriological colony counts on standard media follows closely the methods prescribed for milk (see page 94).

Direct microscopic examination. The direct microscopic examination of stained preparations of ice cream is useful for detecting the degree and kind of bacterial contamination of the dairy products and other ingredients of the mix, as well as the bacteria, yeasts, and molds of the fruits, nuts, and stabilizers and colors."'

Colon group (Escherichia-Aerobacter) determination. These organisms are determined in ice cream by means of the same methods as in milk. Formate-ricinoleate broth has been found by some workers a more dependable medium for the detection of the colongroup bacteria in ice cream than was the Brilliant Green bile broth when only the presumptive test was employed (see page 94).

Anaerobic spore test. Weinzirl and Harris applied this test to ice cream as an index to manurial pollution. The method consists of adding 1 milliliter of ice cream to 10 milliliters of sterile water in each of five sterile test tubes, each, containing about 2 milliliters of sterile vaseline, and incubating at 37° C. for 96 hours. A positive reaction is indicated by a gassy fermentation in three or more of the five tubes.

Reductase test. Macy found that cream could be graded into classes similar to milk (see page 95) if the concentration of the methylene blue solution is tripled, namely, by dissolving 3 tablets instead of 1 as for milk.

Supervisory procedure. Product examination. Samples of all the ingredients of ice-cream mix must be taken at the plant, brought to the laboratory in sealed containers, and examined for wholesomeness, cleanliness, and freedom from adulteration.

In the melting of the sample, it is possible that some butterfat may churn out and thus escape uniform incorporation in the rest of the sample. If the cold sample is weighed out, care must be taken that moisture does not condense on the container on the scales, thereby giving a lighter sample than intended, with consequent lower fat recovery. The composition must comply with local standards and with the label on the package.

The bacteriological significance of the plate colony counts of ice cream is about the same as in milk. When the mix is made entirely from fresh dairy products which have not been heated, pasteurization should kill about 99 percent of the organisms; but inasmuch as most of the ice cream is made from ingredients which have been pasteurized, condensed, or otherwise heated, this destruction may run as low as 90 percent. It is reasonable to expect ice cream to average about 5000 to 10,000 colonies per milliliter by the standard plate technic, although some manufacturers do better than this. A high count indicates carelessness, neglect, or some other remedial condition such as dirty equipment, ineffective refrigeration, or raw materials of too high a bacterial content.

With regard to the significance of the determination of coliform organisms, no one has shown that their determination in ice cream should be the same as in milk. Moreover, no one knows just what their significance is. However, as a qualitative, unofficial instrument, their determination is useful in that it serves to indicate any bacterial pick-up in the plant operations. The presence of a few organisms in a sample may be only the survival of a few resistant strains through the pasteurization process. Anything more than several, say 10 per milliliter, indicates an unusual case of resistance or a plant pick-up. No regulatory action concerning their presence in ice cream should be taken until there has been a bacteriological line run of the plant.

If the cause of a high microbic count is not revealed by a detailed inspection of the plant, it may be necessary to locate the trouble by making a line run test. This involves the taking of samples at successive steps in the manufacturing process. Samples are taken at the beginning of the run on each of the raw materials of the mix, and then after each of the storage tanks, the pasteurization, the homogenization, the cooling, the storing, the freezing, the hardening, and the packaging operations. Somewhere along the line, the count will suddenly jump. The treatment or process immediately preceding this sampling station is the incriminated part of the operations.

Inspection of operations. An effective supervision of an ice-cream business requires that the plant be carefully inspected for compliance with the regulations as to its sanitary operation and types of equipment. The procedure is similar to that followed in milk-plant inspection (see page 134). Judkins has outlined the quality control standards for good plant production practices.

The conditions under which ice cream is dispensed at retail require close supervision. Fabian has outlined the necessary sanitary pro-visions as follows:

All scoops and other implements should be kept in flowing water to preclude reproduction and growth of bacteria.

All dishes, glasses, and silver should be washed at a temperature of 140° F. with a 1 percent detergent solution, and then rinsed in clean water at a temperature not below 170° F.

Flavoring syrups and fruits should contain no more than 5000 microorganisms per gram.

Dispensers should be free from communicable disease and should practice personal hygiene.

Ice cream should preferably be sold in the original unopened packages.

Violations of the sanitary code are handled the same as for milk (see page 134).


1. F. W. FABIAN, Chairman, "Report of Committee on Ice Cream Sanitation," J. Milk Technol. 2, 193 (1939).

2. F. W. FABIAN and E. W. COULTER, J. Dairy Sci., 13, 273 (1930).

3. J. H. SHRADER, Food Industries, 8, 16 (1935).

4. "Sanitation Manual for Ice Cream Plants," Internat. Assoc. Ice Cream Mfrs., Special Bul. 38, 1932.

5. A. C. DAHLBERG and J. C. MARQUARDT, N. Y. State Agr. Exp. Sta. Bul. 628, 1933.

6. H. H. SOMMER, The Theory and Practice of Ice Cream Making, Madison Wis., 2d ed., 1935.

7. F. W. FABIAN, J. Milk Technol., 2, 75 (1939).

8. Associates of ROGERS, Fundamentals of Dairy Science, Reinhold Publishing Corp., New York, 1935, p. 44.

9. L. S. PALMER, Am. J. Pub. Health, 19, 601 (1929).

10. "The Food Value of Ice Cream," Internat. Assoc. Ice Cream Mfrs., Bul. 28, 1930.

11. M. M. KRAMER, M. T. POTTER, and I. GILLUM, J. Nutrition, 4, 105 (1931).

12. F. W. FABIAN, Chairman, "Committee Report on Ice Cream Sanitation," 25th Ann. Rept. Internat. Assoc. Milk Sanitarians, p. 330, 1936.

13. A. J. KRoa and D. S. DOUGHERTY, Am. J. Pub. Health, 27, 1007 (1937).

14. A. C. FAY, J. Dairy Sci., 11, 404 (1928).

15. G. I. WALLACE and R. CROUCH, J. Dairy Sci., 16, 315 (1933).

16. O. W. H. MITCHELL, J. Am. Med. Assoc., 65, 1795 (1915).

17. J. BoLTEN, Pub. Health Repts., 33, 163 (1918).

18. M. J. PRUCHA and J. M. BRANNON, J. Bact. 11, 27 (1926).

19. C. P. FITCH and L. M. BISHOP, Proc. Soc. Exptl. Biol. Med., 30, 1205 (1933).

20. G. I. WALLACE, J. Dairy Sci., 21, 35 (1938).

21. F. W. FABIAN, Am. J. Pub. Health, 16, 873 (1926).

22. C. ARMSTRONG and T. PARRAN, JR., Suppl. to Pub. Health Repts. 62, 1927.

23. H. W. HAMILTON, Am. J. Pub. Health, 8, 651 (1918), quoted from Reference 15.

24. J. C. GEIGER, A. B. CROwLEY, and J. P. GRAY, J. Am. Med. Assoc., 105, 1980 (1935).

25. Commission on Milk Standards, U. S. Public Health Service Reprint 634, 1921.

26. F. W. FABIAN, Proc. 35th Ann. Conven. Internat. Assoc. Ice Cream Mfrs., 2, 56 (1935).

27. C. OLDENBUSCH, M. FROBISHER, JR., and J. H. SHRADER, Am. J. Pub. Health, 20, 615 (1930).

28. C. M. DuBois and W. H. MARTIN, J. Dairy Sci., 16, 435 (1933).

29. A. C. FAY and N. E. OLSON, J. Dairy Sci., 7, 330 (1924).

30. F. W. FABIAN and R. H. CROMLEY, Mich. Agr. Exp. Sta. Tech. Bul. 60, 1923.

31. F. W. FABIAN, ibid., Special Bul. 158, 1926.

32. R. E. IRwIN, Chairman, "Rept. of Committee on Sanitary Control of Ice Cream," 22nd Ann. Rept. Internat. Assoc. Dairy and Milk Inspectors, 204, 1933.

33. Laboratory Manual, Internat. Assoc. Milk Dealers, Chicago, 1933, p. 265.

34. J. H. SHRADER, Chairman, "Rept. of Committee on Analyzing Frozen Desserts and Ingredients," Am. Pub. Health Assoc. Year Book 1937-1938, p. 49. See also M. E. PARKER, J. Milk Technol., 2, 87 (1939).

35. J. J. JOHNSON and J. I. ORMOND, J. Dairy Sci., 20, 159 (1937).

36. Standard Methods of Milk Analysis, 6th ed., American Public Health Association, 1934. (a) p. 102; (b) p. 77; (c) p. 95; (d) p. 73; (e) p. 75.

37. T. MosoNNmR and H. C. TROY, The Technical Control of Dairy Products, Mojonnier Bros. Co., Chicago, p. 122, 1925.

38. Methods of Analysis, Assoc. Official Agr. Chemists, Washington, 4th ed., 1935.

39. H. SCHARER, J. Milk Technol., 2, 16 (1939). See also HAHN and TRACY, J. Dairy Sci., 22, 219 (1939), and Caulfield and Martin, ibid., p. 261.

40. Committee on Bacteriological Methods, J. Dairy Sci., 16, 277 (1933).

41. A. H. ROBERTSON, J. Milk Technol., 2, 84 (1939).

42. A. C. FAY, J. Dairy Sci., 13, 40 (1930).

43. J. WEINZIRL and L. S. HARRIS, ibid., 11, 284 (1928).

44. H. MACY, Univ. Minn. Agr. Exp. Sta. Bul. 310, 1934.

45. H. F. JUDKINS, 25th Ann. Rept. Internat. Assoc. Milk Sanitarians, p. 290, 1936.

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