Crystallization in chocolate

Often, foods must be treated as engineering materials. Heat has to be transported so that the components become cooked or harmful microorganisms and toxins become inactivated. Even in the kitchen, mixing involves the mass transfer of liquids and solids to form metastable structures, which are fixed by subsequent treatment by heat or cooling. Heat transfer properties are crucial in the formation of ice crystals in ice cream and fat crystals in chocolate products. Food materials have been used as a source of industrial components soybean proteins to manufacture auto parts in the 1940s, casein to make buttons and knitting pins, and starches in adhesives and thickeners. 

Proper control of the crystalline microstructure leads to products with the desired textural properties and physical characteristics. For example, tempering of chocolate prior to molding or enrobing is designed to control crystallization of the cocoa butter into a large number of very small crystals that are aU in the desired polymorphic form. When controlled properly, the cocoa butter crystals in chocolate contribute to the desired appearance (shine or gloss), snap, flavor release, meltdown rate upon consumption, and stability during shelf life (fat bloom). Similar... 

Fig. 2. Systems used for the investigation of crystallization in "chocolate." The degree of complexity increases from bottom to top. Complicating factors are identified in parentheses.

Uses Emulsifier for foods (esp. shortening), pharmaceuticals, cosmetics crystallization enhancer for solid fats, producing smooth texture and preventing separation vise, reducer, prevents fat blooming and controls rate of crystallization in chocolates... 

Tempering. The state, or physical stmcture, of the fat base in which sugar, cocoa, and milk soHds are suspended is critical to the overall quaHty and stabiHty of chocolate. Production of a stable fat base is compHcated because the cocoa butter in soHdified chocolate exists in several polymorphic forms. Tempering is the process of inducing satisfactory crystal nucleation of the Hquid fat in chocolate. 

Although most of the applications of supercritical particle formation are known in the pharmaceutical industry, some examples can be found with foodstuff. Cocoa butter a relatively high value product has been successfully micronised using the PGSS (particles from gas-saturated solutions) process [4], In this paper we will investigate the production of fine cocoa butter crystals in order to use them for the seeding of chocolate. 

Tietz and Hartel (2000) studied the effects of removing or adding minor components naturally present in milk fat on the crystallization of milk fat-cocoa butter blends. They suggested that at low concentrations, minor lipids act as sites for nucleation and promote the rate of crystallisation and at higher concentrations inhibit crystallisation. They concluded that the presence of minor lipids, at the concentrations naturally occurring in milk fat, were sufficient to affect crystallisation rates, chocolate microstructure and fat bloom formation in chocolate. 

The British Standard method BS 684 Section 1.13 1976 (BSI, 1976d) is similar. However, the sample is deliberately stirred during the measurement in such a way that small fat crystals formed in the upper parts of the apparatus are carried down into the sample, where they act as crystallization nuclei. This causes crystallization to occur in the most stable polymorphic form, making the test more suitable than the IUPAC one for assessing the performance of fat in chocolate manufacture (Rossell, 1986). 

Crystal Growth Design 2003,3, 721-725, is supplemented by a movie WEO (in. mov format) depicting the time sequence of synchrotron X-ray diffraction patterns for the crystallization of cocoa butter in chocolate (see http //pubs.acs.org/ isubscribe/journals/cgdefu/asap/objects/cg034048a/Mazzantivideouip.mov). 

From the snap, gloss and texture of chocolate to the shelf life of frozen foods, crystalline microstructure plays a very important role in the texture, appearance, shelf life and overall quality of many foods. The total amount of crystaUine phase in a food, as well as the size distribution and shape of the crystals within the food, can affect the physical properties of the product. Furthermore, some mataials in food can crystallize in different polymorphic forms so that control of polymorphic transformations may also be necessary. 

Sensory properties are also influenced by particle size. Each crystalline material in a food has a critical threshold detection size, where above that critical size the particles are detected in the mouth and the food has a coarse texture. The critical threshold detection size depends on the properties of the crystals, namely, how rapidly they melt or dissolve in the mouth. Crystals that melt rapidly in a viscous carrier matrix, such as ice crystals in a frozen dessert, can be up to 50 im in size before sensory detection. In contrast, crystals that are hard and dissolve slowly in the mouth, like lactose crystals in sandy ice cream, can be no larger than about 15 gm before they are detected. A fine chocolate will have the majority of particles smaUa-than 20 gm to avoid sensory coarseness. 

The interface between crystals and the rest of the food matrix is another important concern in governing food properties. As noted in the previous section, the hydrophilic nature of sugar crystals in melted chocolate dramatically impacts fluid viscosity, as does the effect of modifying that interface through addition of an emulsifier. 

Controlled crystalhsation (tempering) is a vital step in chocolate production. The aim of tempering is to generate sufficient seed crystals of form V to act as points on which the fats can crystallise. Tempering normally involves a comphcated temperature-shear-time process. Such a process involves ... 

In mixmres of two or more natural fats, as often occurs in processed foods (e.g., milkfat and cocoa butter in chocolate), it is even more difficult to characterize the true phase behavior for crystallization of fats. One approach that has been used to characterize compatibility of fat mixtures is the isosolids diagram (22). SFC melting curves are obtained (by NMR) for various mixmres of the two fats, as seen for cocoa butter and milkfat in Figure 6. Lines of constant SFC for different temperature and composition are calculated and plotted on an isosolids diagram (Figure 7). 

In a sense, tempering of chocolate is done to create a small (<3%) population of seed crystals in the melted chocolate, which catalyze further crystallization of the cocoa butter when the chocolate is subsequently cooled. Through the tempering process, seed crystals in the p polymorph are formed. These stable crystals then... 

Confectionery-Liquors and Liqueur. In chocolate confectionery and for pastry creams, it is the physical properties linked to the fusion and the crystallization of the fat that are essential. For milk chocolate, for coating or in bars, AMF can be used in proportions that depend on its compatibility with cocoa butter, whose properties of hardness and rapid fusion at 35°C cannot be altered. Thus it is currently accepted that AMF with high fusion levels obtained by the fractionation technique can be used. In general, milkfat has an interesting characteristic it inhibits the appearance of fat bloom (133). 

Tietz, R.A., and R.W. Hartel, Effects of Minor Lipids on Crystallization of Milk Fat-Cocoa Butter Blends and Bloom Formation in Chocolate, J. Am Oil Chem. Soc. 77 163-11 (2000). 

Crystallization events in chocolate manufacture include tempering (pre-crystallization), cooling (bulk crystallization), and bloom (re-crystallization). These processes influence a number of important technological (economic) and sensorial attributes of chocolate (Table 1). Much attention has been focused on bloom formation and its influence on color and gloss, and for good reason, since a consumer may never even buy, let alone eat, a moldy-looking confection. However, we are less... 

Diamond, graphite, fullerenes and nanotubes are polymorphic forms (denoted as allotropes for elements) of carbon all exhibiting very different properties. Cocoa butter can crystallize in at least five different ways, the various crystal structures affecting the perception of the epicurean quality of the prepared chocolate, although all forms are chemically identical. 

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