Stabilizers is a term that refers to hydrocolloid ingredients used at levels well under 1% (most often below 0.2%) to “stabilize” the body and texture of ice cream as close as possible to the desirable characteristics of the freshly hardened product.
They do this by controlling the behavior of water. Similar functionality can be found to lesser degrees in other ingredients used at higher levels, notably proteins and complex carbohydrates. Emulsifiers also stabilize body and texture by way of a different functionality.
Ice, ice crystals
Body and texture perception is closely related to the size of ice crystals and air bubbles. Small ice crystals make for smooth texture, while the perception of richness and creaminess is associated with small air bubbles. Unfortunately, scientific laws favor large particles, which represent a major challenge to delivering high-quality ice cream to consumers. Meeting this challenge requires the management of a broad range of composition, processing and distribution variables.
Controlling the growth of ice crystals and air bubbles is directly related to compositional considerations that influence the rheology (i.e. flow, viscosity) of the unfrozen portion of ice cream. The molecular structure of stabilizers is such that it absorbs large quantities of water. That interferes with the movement of water, thereby increasing viscosity. As viscosity increases, ice crystal and air bubble size becomes more stable because there is a reduction in the degree to which water and air can move about in the system and contribute to growth. Stabilizers also bring about other elements of rheology that contribute to the maintenance of a desirable set of eating properties.
Effects are particularly damaging when ice cream is exposed to temperatures above a critical level. Critical temperatures vary with composition, but, on average, fall in the range of about 12F to about 15F. Below the critical temperature for any given mix composition, the degree of freeze concentration of the stabilizer system and other influences on water mobility increase viscosity so that migration of water and air and the subsequent growth of ice crystals and air bubbles are effectively inhibited. This explains the rationale for hardening ice cream as fast as possible, which brings the product below the critical temperature quickly. It also clarifies the need to keep ice cream well below such temperatures throughout distribution.
During the exposure of ice cream to fluctuations in temperature (known as heat shock), ice that melted during any given rise in temperature refreezes onto the crystals that survive. This increases average ice crystal size during each exposure to temperature fluctuation. The inhibition of water mobility by use of stabilizers is an important element in minimizing ice crystal growth as a result of heat shock.
The effect of stabilizers on the rheology of the system also has a significant influence on dipping properties and inhibits lactose crystallization, which is associated with sandiness.
Stabilizers are classically delivered into ice cream as blends of several types, such as locust bean gum, guar gum, tara gum and cellulose gum. The structures and water-absorbance properties of these ingredients are similar, but vary enough to differentiate between them with regard to handling and eating properties. Other ingredients, such as microcrystalline cellulose, carrageenan, cellulose gel, propylene glycol monostearate, etc., function in different ways to carry out a stabilizing functionality.
Stabilization functionality via control of water mobility is not limited to traditional stabilizers. Soluble proteins and complex carbohydrates (as components in maltodextrins, corn syrup solids, etc.), also contribute to modification of mobility of water and air.
The stabilization needs of ice cream vary with levels of fat, total solids and overrun. Requirements also differ between other products such as sherbets, water ices, sorbets and the like. Then there are also the special needs of soft serve, direct-draw shakes, slushes and smoothie products. In all these products, emulsifiers may also directly or indirectly modify the behavior of water and air, but by different mechanisms.
Of course, too much of a good thing (i.e., over stabilization) is bad, resulting in products with less than desirable handling properties and sensory appeal.
In summary, it’s the influence on the behavior of water with regard to its rheology and mobility that makes the fundamentals of “stabilizers” critical to success.
Ask Tharp and Young
For more on stabilization of ice cream and other frozen desserts, join Bruce Tharp and Steve Young, at “Tharp & Young on Ice Cream: Technical Short Course, Workshops, and Clinics.” They have programs in Singapore (June 22 to 26) and Las Vegas (Dec. 2 to 4). Go to www.onicecream.com for coverage, registration, applicable discounts and more, or call 610-675-4424 or 281-596-9603.