Stabilizing Ice Cream

If you’ve ever opened a carton of ice cream and found an unappealing layer of ice crystals sitting on top, you’ve seen why stabilizers are important. Suppressing this crystal growth during temperature abuse of the product is one role stabilizers play.

“Stabilizers provide two primary functions in frozen desserts,” says Allen Freed, president and CEO, Gum Technology Corporation, Tucson, AZ. “The first is to help reduce the crystal size. The smaller crystal size makes the final product smoother and creamier. Also, since freeze/thaw causes the ice crystals to grow, it is beneficial to start with the smallest crystal possible. Stabilizers also help prevent syneresis, which also leads to large crystals forming, creating a graininess which is not organoleptically pleasant. Stabilizers are also used to create various textures and are used in variegates and inclusions to help keep the variegate from bleeding and spreading into the external phase.”

Stabilizers are often used to impart structure and firmness to ice cream, which assists in packaging. Aaron Venables, senior research scientist, FMC BioPolymer, Princeton, NJ, notes: “This is extremely important in extruded novels such as bars and sandwiches. Maintaining defined shapes and firm edges results in efficient packaging procedures and positive customer perception.”

Stabilizers also help to “suppress the effects of altitude abuse, which reduces the occurrence of shrinkage, control the rate of melt and provide protection against whey separation in resale mix or production facilities that have slow hardening operations,” Venables says.

Semantics

Just as stabilizers serve multiple functions, they encompass two functional categories—emulsifiers and stabilizers. “These ingredients are often added as a system with both components,” explains Joe Klemaszewski, dairy applications food scientist, Cargill Texturizing Solutions, Minneapolis. “Commonly used emulsifiers include egg yolk, mono- and diglycerides, polysorbates, and lecithin. These surfactants alter the interfacial properties between the three phases present in ice cream: lipid, water and air. The type and level of emulsifier also affects the functionality of the milk protein naturally present. Emulsifiers affect the appearance (dryness), creaminess, air cell size and melting properties of ice cream.”

The more-restrictive term “stabilizers” traditionally refers to viscosifying ingredients in the ice cream mix, such as hydrocolloids and proteins. “Examples are guar gum, carrageenan, locust bean gum, cellulose-based ingredients, alginates and gelatin,” Klemaszewski says. “Milk proteins also contribute to the functionality of these ingredients, either by their own interactions with water or synergistic interactions with other stabilizing ingredients. Stabilizers primarily work by controlling water in an ice cream mix, thereby affecting mix viscosity, texture, slowing ice crystal growth, improving air incorporation, melting properties and preventing mix separation.”

Stabilizer blends often include mineral-based ingredients such as calcium sulfate and phosphates. These ingredients aren’t typically considered stabilizers, but do affect ice-cream-mix functionality. “Calcium sulfate is used to make a drier ice cream, while phosphates are used to prevent the churning out of fat and to stabilize proteins during heat processing,” says Klemaszewski.

Ingredient concerns

Stabilizer selection begins with a clear understanding of the end product. “High-butterfat and high-solids formulations require less physical stability than lower-fat or nonfat formulations with less total solids,” Venables says. “Many times, lower quality and less-costly options can be used effectively in these higher-fat, higher-solid products. Formulators must also consider how their product will be distributed and stored throughout the country. Poor freezer storage and/or altitude differentials from the point of production to the shelf often require more-specialized stabilization mechanisms to ensure quality.”

Reduced-fat products contain higher levels of water than their full-fat counterparts. In these products, higher levels of hydrocolloids can “control the increased water and to replace some of the mouthfeel imparted by the milkfat,” says Klemaszewski. “Products with reduced fat have different whipping properties than full-fat products, and adjustments to the emulsifiers may be needed.”

High sugar levels in the formulation might compete for water in the system. “Furthermore, too high a level of mono- and diglycerides might render the stabilizers less functional,” cautions Joshua Brooks, vice president of sales, Gum Technology Corporation.

As the trend moves toward healthier, lower-calorie frozen desserts, stabilizers face different challenges. Tim Carter, dairy program manager, TIC Gums, Belcamp, MD, has found that sugar alcohols in the formulation can negatively affect the batch by increasing the viscosity.

“Reduced-sugar products contain higher-molecular-weight carbohydrates, such as polydextrose and maltodextrin, along with higher levels of milk proteins. This combination imparts a higher viscosity to the ice cream mix,” Klemaszewski explains. Therefore, a lower hydrocolloid level is needed to prevent excessive viscosity during processing.

In frozen desserts, fat or sugar reduction corresponds to increases in water or overrun. Ice creams with lower solids and/or higher overrun require additional functionality from stabilizing ingredients.

A hard-pack ice cream mix will be in a liquid state for less than 24 hours and frozen for up to one year. “By contrast, an aseptically processed soft-serve mix can be stored for months before freezing and be consumed less than one hour after freezing,” says Klemaszewski. “Controlling ice-crystal growth is critical to maintaining product quality in the hard-pack product, given it will see a number of temperature cycles. Mix separation is not typically seen in a manufacturing plant. In the aseptically processed mix, the proteins need to be stabilized to prevent coagulation during the high-temperature processing. Cream and serum separation are a concern as the mix is shipped and stored. Ice-crystal growth over time is not a concern, but the churning properties of a soft-serve freezer are different from the continuous freezer used in a plant. Mixing in a soft-serve freezer experiences higher levels of shear, and an emulsifier level and type typically used in a hard-pack product can result in the milkfat churning out of the soft-serve mix. This is especially prevalent in full-fat mix and is described as small pieces of butter in ice cream.”

Factors affecting stabilizer selection include label considerations, flavor, cost, availability, processing, ingredient interactions and shelf life of the frozen dessert. “A primary label consideration is the standard of identity for the product,” says Klemaszewski. For example, frozen custard regulations mandate egg-yolk solids.

Typically, ingredients in dairy products do not interfere with stabilizers. “However, with increasing demand for fortifications such as fiber, vitamins, minerals and omega-3s, care must be taken to ensure proper function and compatibility,” says Bill Shazer, director of R&D, Tate & Lyle Custom Ingredients, Decatur, IL.

On the other hand, some health-promoting ingredients “require stabilizing ingredients to help with processing, while others, such as fiber, can impart stability,” Klemaszewski notes.

Stabilizing solutions

Brooks suggests blends containing locust bean gum, guar and carrageenan are excellent stabilizing systems for ice cream. “The ratios of these gums in the blends will be adjusted as needed, depending on the type of effect that you are trying to achieve,” he says.

Venables recommends using a system with emulsifier, guar and carrageenan in a full-fat, economy product. For a higher-quality full-fat ice cream, he suggests using a system with emulsifer, guar, locust bean gum and carrageenan. A wide range of stabilizers work in light and low-fat ice creams. The same systems can be used as in full-fat products, but at higher levels. He also recommends a combination of cellulose gel, emulsifier, cellulose gum and carrageenan.

“Some of the major developments include improved forms of microcrystalline cellulose (cellulose gel) exhibiting improved hydration properties, and thus higher degrees of functionality, in ice cream applications, such as more effective foam stability and improved fat-mimetic properties,” Venables says. “Other developments include stabilizer blends consisting of specialized emulsifiers capable of interacting with the fat to coat ice crystals and prevent their growth throughout the shelf life of the ice cream.”

Earlier this year, Cargill introduced a range of stabilizers for aerated water-ice formulas “to give products with a texture described as creamier and more candy-like,” says Klemaszewski. Products developed with this ingredient “have been described as having a texture similar to frozen marshmallows,” he says. “Other formulas with this same stabilizer are creamy and, when combined with cocoa, produce a product with a dairy taste and texture, but can be made without dairy ingredients.” Cargill also has a range of stabilizers for reduced-fat ice creams that utilize traditional equipment. These “still deliver a creamy texture,” he says.

Tate and Lyle Custom Ingredients “uses ingredient technology—combining hydrocolloids, food starches and emulsifiers—to produce body and texture on standard pasteurization and freezing equipment, eliminating the need for the heavy capital investment that national brands experience,” says Shazer.

According to Michelle Ludtke, senior food technologist, Grande Custom Ingredients Group, Lomira, WI, the company’s functional whey protein concentrate “can be used to add a full-bodied mouthfeel and texture to ice cream. It can also be used to reduce or replace skim milk, reduce the milkfat and, therefore, cost. The level depends on the percent of other ingredients replaced and the mouthfeel desired.

Ludtke recommends a starting use level of 2% if the functional whey protein concentrate is replacing skim-milk solids. If both skim-milk solids and milkfat are being replaced, she suggests a 5% level. Higher percentages can help develop a product with a thicker mouthfeel with mild, milky flavor. Ice cream samples containing this ingredient “have seen reduced incidences of ice-crystal formation, especially on the surface over a period of time,” she says.

Although ice cream manufacture is not new, there are always new developments. “Since manufacturers are always looking to create a new frozen item, they are constantly challenging us to create new textures or to develop a system that will allow an inclusion that was not possible before. The development of new machinery also allows creations that were not possible before, and therefore creates new stabilization challenges,” says Freed.