Use the right sweetener systems, stabilizers to avoid heat shock in gelato
We call the relatively high temperatures in a gelato cabinet the ‘danger zone.’ To mitigate heat shock, use the right sweetener systems and stabilizers.
Gelato is most commonly presented for sale in a dip shop as a semi-solid product characterized by intense color and flavoring. Composition of gelato varies widely and may be positioned as gourmet, super premium or other market terminologies. Gelato generally conforms to the U.S. Food and Drug Administration’s Standard of Identity for ice cream, including the descriptors low, reduced and no fat, and/or no sugar added.
When packaged, gelato is most frequently sold in small containers (one pint or less) which may or may not be hand packed or hardened. Sometimes clear containers are used to leverage the product’s visual appeal.
In the dip shop context, gelato is usually dispensed from a batch freezer at intermediate overruns into long shallow trays. Open trays of product are most often decorated and displayed at a high level of visibility in freezer storage cabinets at closely controlled temperatures between 10 F to 18 F, depending on composition, desired stiffness and eating properties. We refer to this temperature range as the “danger zone” since exposure there accelerates the degeneration of textural properties through growth of ice crystals and air bubbles.
Ice crystals grow through recrystallization and ripening. Recrystallization occurs as a result of heat shock; that is, when the water that melts during warming refreezes on existing crystals as the temperature decreases. This effect increases as product temperature increases and freezing point decreases. Ripening involves the migration of water in the unfrozen portion from small to large crystals. It occurs even when temperature is stable. Similarly, air bubble growth occurs as a result of the migration of air from small to large bubbles in a process known as disproportionation.
Ripening and viscosity
The rate of ripening and disproportionation increases as viscosity in the unfrozen portion decreases. At temperatures in the danger zone there is a relatively low degree of freeze concentration of solids in the unfrozen portion. As a result, viscosity is relatively low, which increases the mobility of air bubbles and water, which, in turn, increases rates of growth of both. Also of concern is that the danger zone temperature range includes the steepest part of the water frozen vs. temperature curve, which increases the amount of water involved in recrystallization produced by any given heat shock exposure.
Because of all this, management of the body and texture properties of gelato takes on added importance. Primary factors include: freezing point as it affects the amount of ice at any given temperature; the effect of “freeze concentration” on viscosity and water mobility in the unfrozen portion; and the extent of heat shock exposure. These influences are complex and critical to maintaining sensory appeal.
Stabilizers to control water mobility
Water mobility control requires proper selection of stabilizer systems. Particularly effective are carob bean gum and microcrystalline cellulose. Microcrystalline cellulose is also an effective foam stabilizer that can minimize air bubble growth by restricting the influence of disproportionation. Other considerations consistent with market positioning can be used.
Freezing point management involves achieving the highest possible freezing point consistent with achieving target sensory properties. Since freezing point management focuses on the management of the number of molecules in true solution, the primary way to manipulate the freezing point is via the sweetener system. Processors must aim for the lowest level of sugar needed to achieve any targeted sweetness.
Using monosaccharides such as fructose and dextrose should be avoided since they have about twice the freezing point depression effect of disaccharides like sucrose. It would also be appropriate to consider raising freezing point while maintaining sweetness by replacing some of the sucrose with one or more high-intensity sweeteners.
It is also important to maintain total solids through the proper selection and use of bulking agents, which are also useful for controlling water mobility (e.g., low D.E. starch hydrolysates). In considering ingredients to accomplish all these effects, gelato manufacturers must take into account non-functional considerations related to consumer expectations, such as the use of genetically modified ingredients, clean label initiatives and the like.
Heat shock exposure can be managed by minimizing temperature fluctuations in the display cabinet and throughout the distribution of packaged products.
As we have noted many times, managing the behavior of any frozen dessert involves the same compositional, ingredient, manufacturing and handling considerations whether that product be formulated for dip shop presentation and consumption, or packaged for conventional storage, distribution, sale and consumption.