As we have often noted, ice cream is the only food intended to be consumed frozen. Thus, dairy processors need to protect that which fails first, i.e., body and texture (which can be described as bite, chew, smoothness and creaminess.)
Demands related to cost avoidance/reduction and the ever-changing regulatory environment add physical stress.
With regard to regulatory considerations, coping with the pending increase in serving size (from one-half cup to two-thirds cup) and nutrient content declarations related to fat, sugars, “added sugars,” calories and such, will be necessary. That will include increasing overrun, adding stress to an already stressed ice cream microstructure.
Nearly all products, as now formulated, are affected. However, novel ingredient and process technologies can be useful in managing changes that will be necessary.
Consider the body and texture factors directly related to overrun. These factors require creating, strengthening and maintaining the stability of small air bubbles and small ice crystals to create and retain appealing smoothness, richness and creaminess.
Air cell walls (called “lamellae”) need to be strengthened to minimize growth that is produced by coalescence and disproportionation. It is also important to minimize and stabilize the size of ice crystals. Much can be managed (directly or indirectly) by modifying the behavior (viscosity) of the unfrozen portion of the ice cream.
Several innovations deserve consideration. For example:
Managing properties at high overrun. Lactic acid esters of mono- and diglycerides are reported to be especially effective in promoting the stability of small air bubbles at higher levels of overrun (> 130%) by strengthening air bubble lamellae.
Microcrystalline cellulose (MCC) is also valuable in maintaining the integrity of small air bubbles. Recently, improved forms of MCC have been developed that provide enhanced functionality at lower use rates.
Pre-aeration is the incorporation of overrun in ice cream mix before it enters the freezer. It has been found to promote small air bubbles with inherent resistance to growth during manufacturing, storage, handling, distribution, sales and, ultimately, conditions of consumption. Pre-aeration also has been found to be useful in minimizing ice crystal growth.
Use of alternative gases for overrun. Air bubble growth via disproportionation requires the diffusion of air out of air bubbles. The rate of diffusion is directly related to the vapor pressure of the gas. The replacement of air with argon, a gas with a lower vapor pressure, has been shown to inhibit the increase in air bubble size by reducing the degree of diffusion that takes place.
Minimize ice crystal growth
Using ultra-low draw temperatures. Conditions in the freezer barrel are the most favorable to create small ice crystals. Lower draw temperatures increase the amount of ice formed under those conditions. Thus, it is important to take advantage of innovations with regard to freezer design (a variety of novel designs are available) and freezer operating conditions.
Partial cryogenic hardening (PCH). Rapid hardening is important to the management of ice crystal size. PCH is an innovative approach where a portion of semi-frozen ice cream emerging from the freezer is extruded into small “bits” that are cryogenically frozen in liquid nitrogen and added back into the semi-frozen ice cream.
The presence of these extremely cold bits substantially accelerates hardening. This is especially significant at the relatively high temperatures first encountered in the hardening process, when the growth of ice crystals (via ripening) and air bubbles (via disproportionation) is rapid. After hardening, bits become indistinguishable from the ice cream from which they were formed.
PCH essentially hardens the ice cream from both inside and outside, thus dramatically improving body/texture and shelf-life. The process is particularly valuable in offsetting negative effects of compositional changes in the mix.
Water control index. The rheology of the unfrozen portion of ice cream significantly affects the growth of ice crystals and air bubbles, and is affected primarily by high molecular weight carbohydrates and proteins under the further influence of freeze concentration during whipping/freezing/hardening.
WCI provides a quantitative measure of the degree to which compositional changes influence the behavior of water in the unfrozen portion. As such, WCI is a useful tool in the evaluation of compositional changes based on water mobility management and its role in interfering with water mobility to minimize ice crystal and air bubble growth.
Ultimately, ice cream microstructure is a critical element in the acceptance of any ice cream. Innovative concepts and approaches can be useful in the management of the daunting array of variables that affect the nature of that microstructure.