QShould ice cream melting behavior be used as part of a quality assurance program?
AMeltdown behavior provides insights into key ice cream phenomena, such as protein stability, fat agglomeration and air cell size, which influence body, texture, and other sensory characteristics. Furthermore, meltdown is an important part of any consumer's perception of product quality. Therefore, meltdown is a quality characteristic that should be evaluated alongside flavor, body, texture and appearance.
The evaluation can be limited to vanilla ice cream, in which it is not affected by inclusions. Inferences drawn from vanilla will apply to all products made from the same mix. Meltdown is easily observed by placing a small controlled portion of ice cream on a dark surface before proceeding with other sensory evaluation elements. At an appropriate and standard time, the nature of the meltdown can be observed.
It is often said that "ideal" melting behavior for ice cream involves melting into a smooth, homogeneous fluid that resembles the mix from which it was made. Achieving this "ideal" meltdown behavior is not always compatible with other factors affecting ice cream structure. That is, "ideal" meltdown is often sacrificed to develop structural characteristics needed during post-freezing manipulation, extending shelf life via control of ice crystal growth and/or otherwise modifying eating qualities. So, the question is not whether meltdown is "ideal," but how it changes batch-to-batch.
Factors affecting meltdown behavior of ice cream include composition, mix processing, the influence of shear during mix handling and freezing and the effects of freeze concentration during freezing and hardening. The amount and type of fat, total solids and stabilizer/emulsifier system, as well as mix processing "history," can modify meltdown significantly. As a result, meltdown behavior can provide critical insight into the nature and consistency of a range of quality influences. Shear variability can add more or less fat agglomeration that provides a structure important to many packaging operations and essential in extruded products. It also contributes to the creaminess and richness of ice cream. However, substantial fat agglomeration also is responsible for extreme shape retention, referred to as a "slow melt," and/or an unattractive dry, flaky surface condition on the melted product. Freeze concentration affects meltdown through the irreversible gelling of some stabilizer or milk protein systems. This gel can produce a structure that retains some of the ice cream's volume and forms an amorphous, somewhat rounded, mass or a thick, viscous fluid. Thus, fat agglomeration, freeze concentration, and protein destabilization all influence meltdown behavior.
Major elements that describe meltdown behavior are as follows:
Foamy describes a significant presence of air bubbles in the melted ice cream. Although a slight foaminess is acceptable, excessive foam should be considered a defect. Its principal cause is a thickening or gelling caused by destabilization of the proteins and/or certain stabilizer blends.
Too fast/too slow are terms used to describe the rate at which the ice cream retains its shape as it melts. A very rapid loss of shape ("fast" meltdown) is often associated with weak-bodied products. The retention of shape after the ice has melted ("slow" meltdown) can be caused by factors such as: high solids; low overrun; gelling associated with destabilized protein or some stabilizer systems; and/or substantial fat agglomeration. When the latter is the cause, the melted ice cream will retain most of its physical shape and surface features, with little or no loss of fluid.
Flaky and curdy are useful terms to distinguish between two forms of a condition in which flecks of material can be seen either on the surface of the melt (flaky) or distributed throughout it (curdy). The floating material is made up of tiny portions of the agglomerated fat matrix, while that within the melt represents destabilized protein. Both those conditions are useful indicators of the consequences of composition and processing conditions. (For more details see Tharp & Young On Ice Cream column in the February 2003 edition of Dairy Foods.)
Serum/whey separation is self-explanatory and often associated with the curdy character. It is the direct result of protein destabilization.
The simplicity of observing meltdown behavior and its usefulness in assessing a broad range of quality attributes make it an important part of any ice cream quality assurance program.
Join Bruce Tharp and Steve Young at Tharp & Young On Ice Cream Technical Short Course, Workshops, and Clinics, November 29-December 1. 2006, Las Vegas, Nev. Tharp & Young also offer custom, on-site training programs to cover specific needs held at mutually acceptable locations and times. Free no obligation proposals are available. For information go to www.onicecream.com or call 610/975-4424 or 281/596-9603.