The Ice Cream Evolution

 The Ice Cream Evolution
October 1996 -- Cover Story

By: Scott Hegenbart
Senior Editor

  Ice cream has been a popular dairy food for hundreds of years. History has many stories about its invention, and many countries claim to be the birthplace of ice cream as we know it. It is, however, more likely that ice cream wasn't actually invented by any one person nor in any single country, but evolved over the years. This evolution continues as product designers create new formulas with the seemingly divergent trends toward both higher-fat levels and low- and no-fat ice cream. Understanding basic ice cream composition and how it came into existence helps product designers formulate those products that continue the evolutionary process.

Richness over time

  Reducing the fat level of ice cream is actually taking a trip back in time. Frozen desserts date as far back as the Roman Empire when the elite would send slaves to the mountains to gather snow and ice. Upon their return, a chef would combine what hadn't melted with fruit juices and honey to make a cool, non-fat dessert with a texture resembling a modern snow cone.

  During the Renaissance (13th to 16th centuries) water ices remained popular, albeit primarily with nobility and other members of the privileged upper classes. This period also saw the recipe change to include milk or cream. This made the product taste richer and sweeter and helped smooth the texture into something resembling contemporary sherbets.

  In the first half of the 17th century, many historians believe that Charles I of England first served ice cream as we know it at a state banquet. Some sources credit Charles I's French chef with the "invention" of ice cream, while others maintain that using ice and snow to freeze the product rather than including them in the formula simply was the next step in the evolutionary process.

  Regardless of how it happened, historical documents show that modern ice cream already was established as a dairy product by colonial times. In a New York newspaper dating to 1774, for instance, a caterer announced that he would be offering for sale various confections, including ice cream. In 1813, records show that Dolly Madison served ice cream at the Inaugural Ball of her husband, President James Madison.

  With the invention of the hand-cranked freezer in 1846, ice cream ceased to be hand-made in a large bowl. Soon after, the first commercial ice cream production began in 1851. It took until around 1926 before the original batch process gave way to the continuous freezer.

  In spite of its long history, the formulation and manufacture of ice cream continues to evolve. Product designers creating premium and reduced-fat ice creams have contributed much to this evolution. Advances in the understanding of ice cream structure, ingredients and processing also have helped refine ice cream formulation.

Structure fundamentals

  Modern ice cream is both an emulsion and a foam (the latter technically being an air/liquid emulsion). The milk fat exists in tiny globules that have been formed through homogenization.

  Many proteins in the formula act as emulsifiers to give the fat emulsion its needed stability. Added emulsifiers in ice cream actually reduce the stability of this fat emulsion by replacing proteins on the fat surface. When the freezer aerates the base, the fat emulsion begins to partially break down and the fat globules begin to destabilize. The air bubbles forming in the freezing base are stabilized by this partially coalesced fat. Without emulsifiers, the fat globules would resist this coalescing because of the proteins being adsorbed to the fat globule. This would then cause the air bubbles to be unstable and alter the ice cream's smooth texture.

  Ice crystal formation also contributes to ice cream structure. Water will tend to freeze out of a solution as pure ice. In a sugar solution such as ice cream, the initial freezing point of the solution is lower than 0°C because of the freezing point depression caused by the sugar.

  Freezing point depression is a colligative property of a solution -- in this case, the ice cream base -- and is related to the total number of molecules dissolved in that solution. Lower-weight molecules tend to depress the freezing point to a greater degree. For example, monosaccharides like glucose and fructose would lower the freezing point of the base below that of one sweetened with an equivalent amount of sucrose.

  Why is freezing point so important to consider during formulation?

  Ice cream has some unfrozen water associated with it at the typical serving temperature range of -15°C to -18°C. Without this unfrozen water, the ice cream would be too hard to scoop. On the other hand, if the freezing point is not depressed enough, too much water will be frozen and the resulting ice cream will be too hard both for processing and subsequent consumption.

  In addition to simple freezing point depression, this phenomenon is enhanced by freeze concentration. As ice crystallization begins, the concentration of the remaining sugar solution increases, lowering the freezing point of the remaining unfrozen base. Freeze concentration continues to very low temperatures. Even at the typical ice cream serving temperature of -16°C, only about 72% of the water is frozen. The rest remains as a very concentrated sugar solution leaving the finished ice cream soft enough to be scooped and chewed at freezer temperatures.

  A description of ice cream structure can be summarized, therefore, as a partly frozen foam with ice crystals and air bubbles occupying a majority of the space. The tiny fat globules, some of them flocculated and surrounding the air bubbles, also form a dispersed phase. Proteins and emulsifiers in turn surround the fat globules. The continuous phase consists of a very concentrated, unfrozen solution of sugars.

Ice cream building blocks

  Ice cream structure begins with a foundation in ingredients. Generally, a formula for ice cream base will contain:

  Milk fat provides many functions besides adding rich flavor to ice cream. It also contributes smooth texture, body and good melting properties. On the manufacturing side, milk fat helps lubricate the freezer barrel, allowing the smooth passage of the increasingly viscous base as it freezes. In fact, most ice cream machinery was designed around this lubricating effect. This caused many production headaches when low- and non-fat ice cream manufacturing was first attempted.

  For rich, clean flavor, the best source of fat is milk fat from fresh milk. At the same time, milk fat's other properties also provide unique characteristics.

  Milk fat triglycerides melt in the range from -40°C to +40°C. This means that no matter what temperature the base or the finished ice cream is at, a combination of liquid and crystalline fat will pretty much always exist. Altering this solid:liquid ratio has the potential to affect the amount of fat destabilization in the base.

  When ice cream is frozen, the fat emulsion will partially destabilize by the physical shearing of the mixer blades, the formation of ice crystals and the stress of aeration. This destabilization is called "churning" and is a critical component of the expected structure of the finished ice cream. If the destabilization is altered, the structure and eating quality of the finished ice cream may be altered as well; not always for the positive.

  Non-fat milk solids, or "serum solids" are comprised of lactose, casein, whey protein and minerals. These solids are critical to ice cream texture and body. They also help obtain a higher overrun without negative effects on the texture.

  Milk and cream used in the formula will contribute a certain level of solids, but additional sources are almost always necessary for optimum quality. Additional solids may be added through concentrated skim milk, sweetened condensed whole or skim milk, superheated condensed skim milk, frozen condensed skim milk, and low-heat, spray-dried skim milk powder. Other sources of serum solids include buttermilk powder or condensed buttermilk, condensed whole milk, or dried or condensed whey.

  The benefits gained from added solids, though, do have a limit. High solids levels can contribute off-flavors or even cause a sandy texture when excess lactose crystallizes out of solution. Excessive lactose concentration in the serum phase also may lower the freezing point of the base to an inappropriate temperature.

  In addition to the overall functional contributions of solids, the individual solid fractions have specific properties. Of the solids, around 4% of an ice cream base will be made up of the proteins which are major contributors to ice cream structure in and of themselves. Proteins affect the emulsification and aeration properties of the base and have water-holding capabilities that not only enhance the viscosity of the base, but can reduce iciness in the finished ice cream.

  Sodium citrate and disodium phosphate decrease milk fat's tendency to coalescence. In soft ice cream, this reduces churning and yields a wetter product. Calcium and magnesium ions, on the other hand, promote partial coalescence and help produce a drier ice cream. Balancing the dryness of the frozen ice cream is important for packaging considerations.

  Sweeteners are one of the least expensive sources of total solids for an ice cream formula. At the same time, they improve the flavor and texture of the ice cream. All sugars, including the lactose contributed by milk components, will depress the base's freezing point -- a critical factor in ice cream production that will be discussed later in this article.

  Sucrose is ordinarily the primary sweetener in an ice cream formula because it imparts a clean flavor and the expected freezing point depression properties. Nevertheless, it is now common to replace some of the sucrose with corn sweeteners.

  Corn syrup, for example, can contribute a firmer and more chewy body to ice cream, is an economical source of solids, and can improve the ice cream's shelf life. Available both as a liquid and as dried solids, corn syrup's functional properties in ice cream vary depending on the dextrose equivalent (DE). As a measure of the degree of starch hydrolysis, a higher DE will indicate a higher sweetness and a decreased overall molecular weight. The latter will increase the freezing point depression of the ice cream base. Lower DE corn syrups also contain more dextrins than the higher DE corn sweeteners. These can help immobilize water and contribute to stability against coarse texture.

  High-fructose corn syrup (HFCS) also can be used as an effective sweetness replacement for sucrose. HFCS, however, will tend to depress the freezing point to such a great degree that the finished ice cream may be too soft for dipping.

  Product designers must balance the effects of sweetness, total solids and freezing point when devising the sweetener system of an ice cream formula.

  Stabilizers -- often polysaccharides of some sort -- help add viscosity to unfrozen ice cream base. The stabilizers' affinity for water is also useful in the finished ice cream because it helps reduce migration of any free moisture. Smaller ice crystals are less detectable on the tongue. Immobilizing water maintains the ice cream's smooth texture by slowing ice crystal growth.

  In the early history of ice cream formulation, stabilizers were not as prevalent as they are today. Now, the extensive national distribution channels and the various stages the ice cream passes through from manufacturer to consumer necessitate their increased use.

  At each stage of distribution -- from manufacturer to warehouse, warehouse to distributor, etc. -- the ice cream has a chance to warm up, partially melting some of the ice crystals. When the product is then put back into storage, the crystals refreeze. With each successive freeze/ thaw cycle, the melted ice crystals can migrate, combine and refreeze into larger crystals. Each time this happens, the crystals become larger and cause the ice cream to become gritty and icy tasting. This is called "heat-shock" and its prevention is the primary function of stabilizers in contemporary ice cream formulas.

  In addition to this, stabilizers also help to make the product uniform and resist melting; aid in suspending particulates in the base; help stabilize aeration; make the product clean cutting at the packaging stage; and prevent shrinking and drying-out during storage.

  But stabilizers have limitations that designers must consider. First, it is possible to use them in such a way as to cause the ice cream to melt in an undesirable manner. In fact, an over-stabilized ice cream can give the appearance of not melting at all. Over-stabilized ice cream base often tends to be excessively viscous causing manufacturing problems. Finally, over-stabilized ice cream may have an overly heavy body when eaten.

  When the stabilization of ice cream began, nearly all manufacturers used gelatin. Over the years, this has given way to a variety of other, primarily plant-based, polysaccharides. These tend to be more effective than gelatin and cost less to use at the levels necessary in ice cream.

  The most common ice cream stabilizing ingredients include: carboxymethylcellulose, locust bean gum, guar gum, carrageenan and sodium alginate. Each of these has unique characteristics and has specific advantages and disadvantages. The specific functional characteristics of the various stabilizers also frequently work synergistically with one another. Consequently, many manufacturers use combinations of two or more stabilizers -- often purchased pre-blended from a supplier.

  Emulsifiers help create the proper fat structure and distribution of air in ice cream. These are essential for smooth texture and proper meltdown in the finished ice cream.

  Although the lipophilic and hydrophilic ends of an emulsifier molecule tend to reduce the interfacial tension between two phases of an emulsion, emulsifiers tend to destabilize the fat emulsion in ice cream. Still, the proper level of destabilization is required for the ice cream to be smooth and dry and to melt properly.

  Originally, the emulsification of ice cream base came from the lecithin and protein found in the eggs added to the formula. Now, two emulsifiers perform this function in a more consistent manner: mono- and diglycerides and polysorbate 80.

  Besides the general base ingredients, ice cream normally contains a wide variety of flavors and inclusions. Although issues of flavor use as it affects product quality will be discussed where appropriate in this feature, more information on the creation and application of ice cream inclusions can be found in "Ice Cream Inclusions: Deep Freeze Delights," in the July 1994 issue of Food Product Design.

Process parameters

  Once the formula has been determined, the basic manufacturing steps in ice cream are as follows: