Improve ice cream texture using ultra-low temperatures.

Ice cream today has a well-known composition. It's greater than 10% milkfat by legal definition, although some premium ice creams can have between 10% and 16% fat content. There's between 9% and 12% milk solids-not-fat, the component that contains the proteins (caseins and whey proteins) and carbohydrates (lactose). There usually is from 12% to 16% sweeteners, often a combination of sucrose and glucose-based corn syrup sweeteners. Ice cream also has 0.2% to 0.5% added stabilizers and emulsifiers. The balance, usually 55% to 64%, is the water that comes from the milk.

Ice milk is very similar to the composition of ice cream but contains between 3% and 5% milkfat. Light ice cream contains between 8% and 10% milkfat. The ingredients used to create this composition include: a concentrated source of milkfat, usually cream or butter; a concentrated source of the milk solids-not-fat component, usually evaporated milk or milk powder; sugars, including sucrose and glucose solids, a product derived from the partial hydrolysis of the corn starch component in corn syrup; and milk.

The stabilizers, usually polysaccharides, add viscosity to the unfrozen portion of the water and hold this water so that it cannot migrate within the product. This results in an ice cream that is firmer to the chew. Without stabilizers, ice cream would become coarse and icy very quickly due to the migration of this free water and the growth of existing ice crystals. The smaller the ice crystals in the ice cream, the less detectable they are to the tongue. Especially in the distribution channels of today's marketplace--the supermarkets, the trunks of cars--ice cream has many opportunities to warm, partially melt some of the ice, and then refreeze as the temperature once lowers. Every time this happens, the ice cream becomes more icy-tasting. Stabilizers help to prevent this.

In traditionally processed ice cream, about 40% of the water is frozen when the mixture exits a scraped-surface freezer at about 21 F. The balance of the water is frozen in a hardening tunnel at approximately 40 F. This environment leads to the formation of relatively large ice crystals and gives the product a rough texture.

Even completely frozen ice cream is still plastic. It might be transported and frozen at lower temperatures, yielding smaller ice crystals and a better texture. Scientists at Switzerland's Institute of Food Science use a twin-screw extruder cooled with liquid nitrogen to create an ultra-low-temperature environment for processing ice cream. The mixture is fed by a pump and is kept under pressure to retain entrained air.

Exit temperatures are close to 0 F. No further hardening is required, so there's no need for hardening tunnels that might require a significant capital investment. Not only does this ultra-low-temperature process yield an improved product, we're told, but it also uses less energy.

Further information. Erich Windhab, Institute of Food Science, D-AGRL, LFO E 18, ETH Zentrum, CH-8092 Zurich, Switzerland; phone: [phone]; fax: [phone]; email: [e-mail].