Each year at SLA, the Sci-Tech or Chemistry Division presents a session on a subject of general interest, usually related to food. Last year we heard about hot peppers and salsa; previous sessions have been about coffee and beer. These are always fascinating, educational, and enjoyable. This year was no exception; the title was “The Science of Ice Cream”.
Thomas Palchak, Manager of the Penn State Creamery gave an outstanding and detailed look at ice cream to an overflow audience. (Maybe the attendees thought they might some samples, but unfortunately none were available.)
History of Ice Cream
The Romans made the first water ices in about 100AD. Only the upper elites were able to afford it. Crystalline sugar dates from Persia in 627AD. Beet sugar in the 19th century caused prices to drop so the masses could afford sweetened products. Ice cream became a sensation at the White House in 1812 at President Madison’s 2nd Inaugural Ball. Ice cream as we know it today was became available in the US with the development of large scale freezing. The first freezer was patented in 1843, and the first ice cream plant was established in 1851 in Baltimore. In 1892, Penn State University offered the first course in ice cream manufacture. Today, ice cream production is 1.6 billion gallons/year. Annual consumption in the US is 24 quarts per capita, second only to New Zealand (26 quarts per capita). Ice cream is a great cementer of memories from childhood; it is one of the few foods with that capability.
Ice cream is unique because it is frozen when eaten. It melts to cool and refresh (its melting is endothermic–heat absorbing), tastes sweet, and its aroma is suppressed until eaten. It is smooth and creamy (producing a relaxed feeling), appearance is important, and it is available in many flavors (the PSU creamery makes over 150 flavors!).
The FDA Standard of Identity for ice cream is fairly rigorous. It must be frozen under agitation for rapid removal of heat and to prevent spoilage. Ice cream is a colloid; air and flavoring are added after pasteurization. Everything else is added before. Kelp is used in small amounts to aid in stabilization and emulsification.
There are a bewildering number of types of ice cream, including:
- Reduced fat: 50% less than the standard market amount of fat.
- Lite: 1/3 of the standard amount of fat.
- Lowfat: 2% fat.
- Nonfat: no fat.
- Gelato: a fanciful name with no standards.
- Dairy sherbet: no more than 2% milk fat.
- Ice milk: any frozen dessert with 7-10% fat. “Ice milk” is becoming obsolete.
- Soft serve: frozen without agitation.
- Mellorine, paravine: obsolete terms for ice cream made with vegetable oil.
- Frozen yogurt: No Federal standard. It can be anything, even with no yogurt.
The roles of the ingredients in ice cream include:
- Milkfat gives richness of flavor and a smooth texture, lubricates the palate, and improves ice cream’s insulating qualities.
- Nonfat solids enhance the texture, increase chew resistance, and prevent the product from being snowy or flaky by protecting against heat shock.
- Proteins contribute to structure development, including ability to foam, which is important because air is incorporated to about 50% of volume. They resist ice crystal formation and help ice cream retain its flavor.
- Sweeteners increase the acceptance of the product. Sucrose is the most commonly used sweetner.
- Stabilizers and emulsifiers are used in small amounts (usually less than 0.4%), but they perform a critical function by increasing the viscosity of the mix and producing stable foam, melt resistance, and a smooth texture. They firm the ice cream and allow longer storage time, and produce a dry and stiff ice cream that resists rapid meltdown.
- Water and air are also important, though their effects are easily disregarded. Water is the solvent. It never completely freezes in ice cream. Air is dispersed in the emulsion and the interface between water and air is stabilized by unfrozen material.
Flavor is the most important characteristic of ice cream. It is not the same as taste, which includes body and texture. Flavor is very subjective and depends on the individual doing the tasting. Delicate over harsh is preferred, only intense enough to be recognized.
Ice cream is a major market for fruit growers. Fruit-flavored ice creams account for about 15% of sales, second after vanilla. Fruit flavors may be variegates, background flavors, and are often enhanced by the addition of fruits, nuts, and candies.
Consumers “eat with their eyes”, so color must be delicate and attractive. Colors must be certified; the term “natural color” is not allowed.
Milk is sterile when secreted from healthy cows; contamination occurs afterwards. It is perishable, easily contaminated, and must be refrigerated at all times. Ice cream is not sterile, does not contain harmful bacteria, and must be pasteurized and homogenized. Every particle of milk must be heated to 175 degrees F and held for at least 25 seconds, which will kill every pathogenic organism. A primary concern is post-pasteurization contamination. Homogenization uniformly distributes the fat throughout the product and prevents separation of the milk. Homogenization is critical for sensory attributes of ice cream and promotes a smoother texture.
The US has the safest milk supply in the world. California, Minnesota, Wisconsin, New York, and Pennsylvania account for over half of the milk supply in the US.
Columnist, Information Today and Conference Circuit Blog Editor