as nicely described in chapter 5, salep dondurma is a fascinating Turkish ice cream. It has an unusual thick and stretchy consistency, which makes it chewy—and yet it also smoothly melts in the mouth. This chapter explores the molecular origins of this stretchy texture and postulates how such textures can be produced in the kitchen using alternative ingredients away from the restrictive confines of ice cream machines.
Novelty in food production, either on a commercial scale or in the home kitchen, often involves changes in product texture, as this is one of the factors controlling the organoleptic quality (taste, odor, color, and feel) of foods. From a consumer perspective, the texture provides an indication of whether a product has a too thick or too thin mouthfeel. Researchers have investigated the molecular properties of salep dondurma. Knowing these properties helps explain the relationship between salep’s structure and its effect on texture. As explained in chapter 5, the main component of salep is a glucomannan (a polysaccharide containing both glucose and mannose). It is similar to that found in the tubers of Amorphophallus konjac, a plant that is widespread in tropical East Asia and is used as source for konjac glucomannan—the sustainable alternative tuber flour employed in making salep dondurma. Konjac glucomannan is used extensively in Japanese cuisine in varying forms, as slabs or balls of gel, as chewy noodles, and as additives in savory condiments, such as soy sauce or mustard, and in weight-control powders that hydrate to form thick, stomach-filling preparations.
The properties of salep in solution are similar to konjac glucomannan and also to certain food thickeners, such as guar gum and locust bean gum, which are generally known as galactomannans. Locust bean gum is known to gel during freezing in the production of ice cream, while salep does not (similar to guar gum and konjac glucomannan). This suggests that the properties of salep, an exotic and increasingly rare ingredient, can be replaced by more conventional additives.
Both guar gum and locust bean gum phase-separate when mixed with milk. Such phase separation is explained by the concept of incompatibility. That is, the polysaccharides and milk proteins occupy their own phase when cosolubilized in water, rather than sharing the available volume as one phase. These incompatible mixtures are known as water-in-water emulsions. These types of emulsions have properties that are similar to incompatible mixtures more often used in the kitchen. Examples of incompatible mixtures are oil-in-water emulsions, such as vinaigrette dressings, mayonnaise, and table spreads.
Figure 9 A typical phase diagram of polysaccharide-protein incompatibility. Certain compositions remain as one phase, but higher concentrations of either protein or polysaccharide tend to phase-separate, and the final composition of each separated phase is determined by where it falls on the tie line.
The phase separation in incompatible mixtures is dependent on the starting composition. Changing the composition will not only change the volume of the separated phases but also the structure of the phase-separated system. As depicted in figure 9, adding more polysaccharide (for instance, locust bean gum) increases the relative volume of the polysaccharide, or black, phase and decreases the relative volume of the protein, or white, phase. If the polysaccharide phase continues to increase, the structure of the phase-separated system will suddenly change, from a system in which the black phase is dispersed in the continuous white phase to the inverse of this process. The white phase will then be dispersed in the black phase. In technical terms, this phenomenon is called phase inversion.
Another consequence of phase separation is phase concentration. This means that the concentration of, for example, the polysaccharide in its phase in the phase-separated system is greater than the nominal concentration in the formulation. Therefore, salep can be replaced only by other, more common ingredients if the phase separation potential for mixing with milk protein can be matched, along with matching the physical properties of the polysaccharide phase.
Two processes that must also be kept in mind when making such formulation considerations are those of heating, typically for pasteurization purposes, and freezing—which is, of course, essential in making ice cream. During heating, water will evaporate, thus increasing the solution concentrations of both the polysaccharide and protein from their starting formulation concentrations. In freezing, water is removed from the salep-containing phase in the form of ice, giving an even more concentrated unfrozen matrix phase within the ice cream product. Therefore, the hypothesis is that the specific stretchy textures are a result of controlled changes in the concentrations in the polysaccharide and protein phases. If the concentration of either the polysaccharide or the protein is too high, then the stretchability of the product is not optimal. Additionally, if locust bean gum is used to replace salep, stretchy textures are not possible because locust bean gum gels during the freezing process.
To test this hypothesis, we heated mixtures of milk and salep or guar gum in a rotary evaporator to drive off water and concentrate the mixture. When the approximate water content of the corresponding unfrozen matrix (in ice cream) was reached, stretchy textures were observed, confirming our hypothesis. This knowledge turned out to be the foundation to successful salep replacement in salep dondurma. In addition, it demonstrates that ice formation is not necessary to create such textures; in other words, we now can make other products with stretchy textures. In addition, it shows the two conditions that polysaccharides have to fulfill to provide salep-like stretchy textures: first, they should show the appropriate phase-separation behavior in the presence of proteins, and second, they should not gel.
Therefore, we can prepare stretchy textures on a kitchen scale, with application to sweet and savory products alike. Furthermore, using the same concepts, we can now control the texture of a wide range of dairy-based products (white sauces, cream cheeses) and soy-based products. Several of the polysaccharides mentioned may be employed as ingredients to create the stretchy textures; however, chefs and cooks can find them difficult to obtain. Alternative sources, which are more readily available, are possible, however. For instance, when mixed with proteins, mucilage gums produced from the cooking of okra provide stretchy textures in kitchen preparations. Okra polysaccharide, exuded from the okra seed pods during cooking, is known to be slimy and shows a tendency for structure formation. Also, it stabilizes foams and can form gels. Therefore, I propose a savory dish in which okra is cooked in the presence of a protein source, like soy flour. The interaction and incompatibility of the naturally exuded polysaccharide mucilage with the protein can then induce the desired stretchy behavior. Along with such an experimental approach in the kitchen, the simple addition of 0.5 gram of, for example, guar gum and ½ ounce (15 g) sugar to 3½ ounces (100mL) of milk or soy milk is sufficient to provide stretchy textures upon either heating or freezing.
It is fascinating to realize how through a fundamental understanding of the physical world, seemingly different food products have more in common than one would ever imagine. It is now your turn to stretch your imagination.
Foster, Tim. 2007. “Structure Design in the Food Industry.” In Product Design and Engineering, vol. 2, Raw Materials, Additives, and Applications, edited by Ulrich Bröckel, Willi Meier, and Gerhard Wagner, 617–629. Weinheim: Wiley-VCH.