Tharp & Young: on ice cream

Dairy Foods, Dec, 2002

Q: What factors cause ice cream to get gummy?

A: The term gummy is used to describe ice cream that is sticky or stringy when dipped. In the mouth it offers strong resistance to structure loss and mechanical manipulation. The effect is reminiscent of eating a gumdrop, hence the name.

Gumminess is related to the rheology of the unfrozen portion of ice cream, which in turn is related to the nature and degree of water immobilization. Although water immobilization is important to control ice crystal growth, a point is reached where the unfrozen product becomes sticky and very cohesive, i.e., gummy. Sometimes some gumminess is desired in ice cream; however in most cases, manufacturers do not want a gummy ice cream. To reduce the degree of gumminess in a product that currently shows that characteristic, several factors should be considered.

The primary considerations affecting water immobilization and therefore gumminess, include the nature and level of stabilizing colloids, high-molecular weight components of corn syrup solids (CSS), some bulking agents (in the case of lower fat products) and milk protein. To reduce (or manage) the degree of gumminess, the amounts and/or types of these components should be adjusted.

The stabilizing colloid most likely to be involved with gummy ice cream is guar gum. If guar gum is a major component of a stabilizer system and gumminess is a problem, the use of an alternative stabilizer like carboxymethyl cellulose can be helpful. Most of the time hydrocolloid level stays the same.

Likewise, water immobilization increases as the CSS dextrose equivalent (DE) decreases. However, the relative benefits of products like 36 DE CSS to ice cream quality and economics are so great, that it is highly desirable to use 36 DE CSS and manipulate the degree of gumminess by adjusting the level of 36 DE CSS or other ingredients.

In similar ways, the water-holding activity of milk proteins impacts gumminess; therefore take care when selecting and using milk proteins in order to manage gumminess effectively.

Q: What effects do pasteurization and homogenization have on ice cream mix functionality and performance?

A: Thermal processing of frozen dessert mix is required by law. Whether it is batch, HTST, HHST (high, high temperature, short time) or UHT pasteurization, thermal processing of ice cream mix exerts several positive effects. Besides rendering the mix pathogen-free, pasteurization also helps inactivate naturally occurring enzymes. Inactivation of microorganisms and enzymes reduces the development of undesirable fermentation and enzymatic byproducts and thus, extends mix shelflife and preserves a mild mix flavor. Heating also prepares the mix for homogenization. Thermal processing melts milkfat and other high-melting point lipids such as emulsifiers, which is critical to effective emulsification. It also hydrates other solids into colloidal suspension or true solution.

Depending on the exact nature of the mix and the specific thermal treatment, positive or negative flavors can result. Slight cooked flavors may be highly desirable by some, whereas more pronounced cooked flavors may not be desirable at all. The same may be true relative to mix color. In addition, depending on the amount and type of ingredients used, more or less functionality could be created during thermal processing. Finally, thermal processing helps prepare a uniform mix.

Homogenization reduces fat droplet size and creates a stable emulsion. A secondary, yet very important effect includes changing the physical and chemical function of the milkfat globule membrane by increasing available surface area. This enables interactions with soluble or colloidally suspended proteins, stabilizers and emulsifiers during mix aging. Increasing mix whiteness and viscosity may occur. Of course, homogenization efficiency and the impact of homogenization varies with factors such as applied pressures, location of the homogenizer in the process, the number of homogenization stages, mix composition, temperature of homogenization and the occurrence of any insoluble matter.

The various chemistries and structures created by pasteurization, homogenization and subsequent mix aging are critical to mix performance during freezing, whipping, hardening and distribution. These, in turn, impact finished product sensory attributes including flavor, appearance, body, texture and overall product acceptability.

JOIN BRUCE THARP AND STEVE YOUNG AT A 2003 THARP & YOUNG ON ICE CREAM PROGRAM. TECHNICAL SHORT COURSES, WORKSHOPS AND CLINICS ARE SCHEDULED FOR NOVEMBER 12-14 IN ORLANDO AND DECEMBER 3-5 IN LAS VEGAS, A NEW RETAILER'S EDITION WILL BE HELD IN PHILADELPHIA ON OCTOBER 4. FOR MORE INFORMATION CALL 610-975-4424 OR 281-596-9603 OR VISIT WWW.ONICECREAM.COM.