Chocolate crystallization

These researchers (Bolliger, Breitschuh, Stranzinger, Wagner and Windhab 1998) worked with a high shear crystallizer (Figure 22.4) in which the chocolate crystals are scraped from the cooled surface into the bulk to act as nuclei for further crystallization. 

Terbium is reasonably stable in air. It is a silver-gray metal, and is malleable, ductile, and soft enough to be cut with a knife. Two crystal modifications exist, with a transformation temperature of 1289oC. Twenty one isotopes with atomic masses ranging from 145 to 165 are recognized. The oxide is a chocolate or dark maroon color. 

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. 

Nucleation tempering of the stiU molten fat is necessary because the cocoa butter, if left to itself, can soHdify in a number of different physical forms, ie, into an unstable form if cooled rapidly, or into an equally unacceptable super stable form if cooled too slowly, as commonly happens when a chocolate turns gray or white after being left in the sun. The coarse white fat crystals that can form in the slowly cooled center of a very thick piece of chocolate are similarly in a super stable form known in the industry as fat bloom. 

A stable crystalline form for chocolate depends primarily on the method used to cool the fat present in the Hquid chocolate. To avoid the grainy texture and poor color and appearance of improperly cooled chocolate, the chocolate must be tempered or cooled down so as to form cocoa butter seed crystals (31). This is usually accompHshed by cooling the warm (44—50°C) Hquid chocolate in a water jacketed tank, which has a slowly rotating scraper or mixer. As the chocolate cools, the fat begins to soHdify and form seed crystals. Cooling is continued to around 26—29°C, during which time the chocolate becomes more viscous. If not further processed quickly, the chocolate will become too thick to process. 

In another method of tempering, soHd chocolate shavings are added as seed crystals to Hquid chocolate at 32—33°C. This is a particularly good technique for a small confectionery manufacturer, who does not produce his own chocolate. However, the shavings are sometimes difficult to disperse and may cause lumps in the finished product (20). Most companies use continuous thin-film heat exchangers for the tempering process. 

The basic chromates are crystals having colors that vary from yellow to chocolate-brown to lilac, depending on their compositions and chromate to hydroxide molar ratios. They lose water when heated at 260°C, are insoluble in water, and are soluble in nitric acid. 

Lactitol. Lactitol (4-0-/ -D-galactopyranosyl-D-sorbitol), is a synthetic sugar alcohol produced on reduction of lactose, usually using Raney nickel. It can be crystallized as a mono- or di-hydrate. Lactitol is not metabolized by higher animals it is relatively sweet and hence has potential as a non-nutritive sweetener. It is claimed that lactitol reduces the absorption of sucrose, blood and liver cholesterol levels and to be anticariogenic. It has applications in low-calorie foods (jams, marmalade, chocolate, baked goods) it is non-hygroscopic and can be used to coat moisture-sensitive foods, e.g. sweets. 

Figure 6. Ciyo-section of chocolate stained with Nile Blue. The fat (white areas) forms a continuous phase around protein particles and sugar crystals, (darker areas). Epifluorescence optics.(x 490).

Caffeine, the active substance responsible for the stimulant effect of the coffee plant s berry, is a methyl-xanthine, one of the family of stimulants present in more than 60 species of plants. The pure chemical forms white, bitter-tasting crystals, which were first isolated from coffee in 1820. Other family members are theophylline, found in tea leaves, and theobromine, found in the cacao pods that are ground to make chocolate. The most potent component in the coffee family by unit weight is theophylline, while theobromine, the weakest component by unit weight, stays in the body longer than does caffeine. 

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. 

Adding a sucrose ester to chocolate can prevent the unappetising white bloom of cocoa butter crystals which sometimes forms on its surface. In Europe, sucrose esters are given an E-code number, E473, which means they have been passed as safe to be used as food additives in all the countries of the EU. 

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 sensory properties, especially texture and appearance, of milk fat-based products such as butter, cream, cheese, ice cream and milk chocolate are largely dependent on the physical properties of the product, especially properties governed by the phase change behavior of the fat, used here to mean melting and crystallisation behavior, crystal polymorphism and microstructure (Birker and Padley, 1987 O Brien, 2003). The same may be said of the functional properties of milk fat, milk fat fractions and milk fat-based products when these are used as food ingredients. 

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). 

When it comes to predicting the point of crystallization, it gets more complicated. Crystallization of oils or fats or of FAME is a thermodynamic process. FAME crystallization by itself is probably much simpler than the complex crystallization of oils and fats as seen in food products from chocolate to margarine. Basic research on FAME crystallization is in progress, but currently not readily available to put in a simple and useful mathematical model sufficient to describe the CP, PP, or CFPP. 

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