Chocolate tempering

Talbot, G., Chocolate Temper, in Industrial Chocolate Manufacture and Use, edited by S.T. Beckett, Blackie Academic FYofessional, Glasgow, 1994, pp. 156-166. 

At this stage the chocolate is ready for forming into its final shape after it is tempered. The two most common forms are mol ding or enrobing. 

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. 

Molding. The Hquid tempered chocolate is deposited into a metal or plastic (polycarbonate) mold in the shape of the final product. There are three basic types of mol ding soHd (or block), sheU, and hoUow. 

Once my mom told everybody in my class that I was allergic to chocolate, and baaad things happened. They were so mean. They d put chocolate right in my face. That I cannot take. I can resist candy— I ate chocolate just once in school. But I can t take the teasing sometimes. I got angry with them and lost my temper. And I was angry with my mom for a week. 

Flourishing in warm and tropical areas with a few in temperate zones, the Sterculiaccae yield chocolate (cacao), cola nuts, limber, and cultivated ornamentals. 

The appeal of chocolate is universal, but the pleasures of eating chocolate products may perhaps be tempered by their fat and sugar content. However, in a series of human feeding studies it has been shown that the high proportion of stearic acid in the cocoa butter of chocolate does not adversely affect plasma lipids. Two recent reports of antioxidant activity have increased interest in the health aspects of chocolate an in vitro low-density liposprotein (LDL) oxidation study and a short-term in vivo study. Epicatechin, the major monomeric polyphenol antioxidant in chocolate, and an extract of chocolate liquor were both found to stimulate cellular immune response in vitro. 

The powder samples described in series E-I and E-IV (obtained with the smallest nozzle) gave the best results. The seeding was carried out at 305 K (32 °C) with a mass fraction of 0.1-0.2% and produced a well-tempered chocolate. At this high temperature, the stirrer velocity is a critical point as an excess of mechanical energy could melt the seeds, but this has to be tested using an industrial scale tempering machine (batch or continuous). 

A major interest in using this new process [8] is the value of the temperature at which seeding can be done with the cocoa butter particles supercritically generated. At 305 K the chocolate is less viscous, this is advantageous in term of flowability and energy consumption. An additional advantage lies in the fact that the time needed to obtain a well-tempered chocolate is shorter (about 5 min). Moreover, the overall quantity of seeds to temper the chocolate is very small. Therefore, a scaling-up of this process to an industrial scale appears feasible. 

This is based on a cake my mom ofien made. It came from Maida Heatter s Book of Great Chocolate Desserts, except that Mom could never stick to the recipe. The sour cream tempers the cake s sweetness, and the cake itself is so moist that it almost resembles a pound cake in texture. I fill it with Vanilla Whipped Cream tinted in a bright color or Red Currant Curd, and cover it with Sweet Chocolate Ganache. It s the perfect cake for beginners—my husband found my recipe journal and baked this cake for my birthday ... 

Function Tempering aid and antibloom agent in the manufacture of chocolate and chocolate coatings. 

In foods containing crystalline lipids, control of polymorphism is important for making products with desirable material properties and shelf stability. Conditions during processing govern the polymorphic behavior of fat. The process of tempering of chocolate nicely demonstrates these principles. 

Haedelt, J., Pyle, D.L., Beckett, S.T., and Niranjan, K. (2005) Vacuum-induced bubble formation in liquid-tempered chocolate. J. Food Sci. 70, E159-E164. 

Reddy, S.Y., Full, N.A., Dimick, P.S., and Ziegler, G.R. (1996). Tempering method for chocolate containing milkfat fractions. Journal of American Oil Chemists Society. 73 723-727. 

Figure 22.1. Good and bad chocolate The well tempered chocolate on top is glossy and has come away easily from the mould. The untempered chocolate sticks in the mould and shows a spotted and marked surface.

The process of tempering - by which the conditions are created for the correct crystal form to be produced - and solidification are thus cmcial to successful chocolate-making. The aim of this chapter is to review work in this area and describe current understanding of the processes and their kinetics. 

Figure 22.2. Pictures of bloomed chocolate due to (A) storage, (B) fat migration, (C) heat hit, (D) over-tempering, (E) non-tempering (Lonchampt and Hartel 2004).

More recent studies have shown that bloom (or dull) can occur for both tempered and untempered chocolate (Lonchampt and Flartel 2004 Lonchampt and Hartel 2006). For untempered chocolate, the blooming essentially comes from the transition from low melting point polymorphs (thermally unstable crystals) to high melting point polymorphs (usually VI). During this transition, the material mobility is increased and the migration of fat crystals to the surface is facilitated. For tempered chocolate the different causes of blooming are ... 

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 ... 

Figure 22.6 (Stapley, Tewkesbury, and Fryer, 1999) shows the apparent specific heat for tempered milk chocolate cooled at different rates obtained using DSC. Different cooling rates shifts the main peak by about 15°C, showing the difference between the tempered material produced at low cooling rates and the untempered material generated at the faster rates. This type of behaviour will occur throughout a cooling chocolate, and must be considered in any model. Outside of the phase change region, the specific heat capaeity shows no dependence with cooling rate.

Figure 22.7. Comparison of model (thin line) and experimental (thick line) temperatures for the cooling of tempered chocolate at a nominal rate of 2 C/min. The model uses apparent specific heat capacity data taken from DSC measurements at a cooling rate of 2 C/min (Tewkesbury, Stapley and Fryer 2000).

A Rodenstock RM600 has been used to follow the shape change of chocolate and obtain an understanding of the nature of the kinetics of crystallisation of chocolates of different temper (Fryer and Pinschower 2000). The equipment consists of an optical distance sensor, with sub-micron vertical resolution, together with a traverse table which holds the sample and allows the sensor to be tracked across it. 

The data can be treated by expressing the height data as a ratio in Figure 22.10(b). This both flattens the data and enables it to be seen more clearly the effect of the cooling of the tempered chocolate is to cause the characteristic cracking at the side of the mould. A comparison of tempered and untempered material is shown in Figure 22.11. The shapes of the two are very different, showing the different profiles of the material. 

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