Tharp & young on ice cream

Dairy Foods, Feb, 2005

Q What mix processing variables impact the eating quality of ice cream?

A Unit operations tip to, but not including whipping and freezing, are considered mix processing. All mix processing variables have significant and complex influence on the eating quality (body, texture and flavor) of ice cream. It is possible here to provide only a broad overview of the relationships involved. Many of these have been considered in greater detail in previous columns. All are addressed in detail fit Tharp & Young On Ice Cream technical short courses.

To start, mix ingredients should have maximum stability with regard to flavor, functionality and, in the case of protein-containing ingredients, protein stability. These elements are particularly vulnerable to deterioration due to the heat and shear applied during processing.

When dispersing ingredients, the use of high-speed mixers should be limited so that no more agitation than necessary is applied; otherwise, protein and fat molecules might become unstable. This can negatively affect mix stability and fat agglomeration in the freezer.

Exceeding pasteurization specifications (time/temperature) can cause quality variations with regard to flavor, color and protein stability. For example, cooked flavors might develop, which can become a problem when cooked flavor is not a normal part of the finished product's flavor profile. Color can deteriorate as well. And, protein molecules can be damaged, particularly, when protein stability has been diminished in one or more dairy ingredients. In the extreme, protein instability produces serum separation in the package and/or a meltdown that is curdy and shows whey separation.

Following pasteurization, it is important to cool the mix to 40[degrees]F or lower. In addition to the inhibition of microbiological growth during storage, a low mix temperature is important to achieving the lowest possible exit temperature at the freezer. This is essential to the initial texture and heatshock stability of the ice cream.

Homogenization should produce a fat globule size distribution of 1-2 microns. Successful homogenization requires all fat components to be liquid, so it should be applied at a temperature above the melting point of all fats present. This is particularly relevant to emulsifiers, some of which have a melting point above 150[degrees]F. Pressures applied should follow the guidelines of the homogenizer manufacturer.

It is also important to ensure that the homogenizer valves fire maintained. Any departure from proper homogenization conditions can have a negative effect on quality related to the desirable fat agglomeration that occurs in the freezer. Effects can include such undesirable characteristics as buttering- poor handling properties at the freezer: weak, short body; greasy mouthfeel: loss of creaminess and richness: and shrinkage.

Such quality defects are also associated with the development of fat agglomeration in the liquid mix after homogenization. This occurs through the application of excess shear during mix transfer as a result of the use of oversized or improperly operated centrifugal pumps or in the turbulence produced by sharp piping angles.

Mix aging is required to prepare the fat to achieve the targeted level of agglomeration in the freezer and thus avoid the negative quality effects of insufficient or excess agglomeration in the freezer. Two critical events occur during aging--complete fat crystallization and conditioning the fat globule surface. Fat crystallization requires about two hours, regardless of the cooling temperature. Conditioning the fat globule surface can extend the required, aging time Lip to four hours, depending on the amount and type of added emulsifier. Frequently used emulsifiers, ranked in order of increasing requirement for aging time, are polysorbate 80, polysorbate 65, unsaturated monoglycerides, saturated monoglycerides and phospholipids (i.e., lecithin alone, or lecithin indirectly through the addition of egg yolk or buttermilk).

During mix storage even a slight degree of serum separation can produce variable quality because of changes in the level and nature of the total solids as a non-uniform mix goes to the freezer. This is why agitation is important during storage. However, too much agitation can have a negative impact by, producing premature fat agglomeration. This affects air incorporation by increasing mix viscosity and causing the defects associated with excess fat agglomeration. Management of storage agitation may involve the use of intermittent agitation through the use of a timer on agitator motors.

JOIN BRUCE THARP AND STEVE YOUNG AT THARP & YOUNG ON ICE CREAM, NOV. 30-DEC. 2, 2005, IN LAS VEGAS. THARP & YOUNG ALSO OFFER CUSTOM, ON-SITE TRAINING PROGRAMS TO COVER SPECIFIC NEEDS HELD AT MUTUALLY ACCEPTABLE LOCATIONS AND TIMES. FOR A FREE, NO-OBLIGATION PROPOSAL, CONTACT THARP & YOUNG AT 281/596-9603 OR 6101975-4424, OR VISIT WWW.ONICECREAM.COM.