Lesson 29 :Processing and Preparation of Sugar and Related Products
A crystal is composed of closely packed molecules arranged in a pattern. Crystallisation occurs only if the solution is supersaturated. The size of the crystals produced will depend on the rate of the formation of nuclei about which the crystals grow and the rate of growth of crystals around the nuclei. If only one or two nuclei are formed, the size of the crystals produced will be large but if the rate of formation of nuclei is very rapid, many small crystals will form. Both the rate of crystallisation and the rate of nuclei formation are modified by many factors.
Microscopic examination of crystals Place a drop of turpentine on a microscope slide and add a very small grain of the candy. Place a cover slip on top and move it around to make a very thin layer of the candy crystals. View under the microscope and compare the size of crystals.
Factors affecting crystallisation
Nature of the crystallising substances Some sugars like glucose do not have the ability to produce very large crystals, rather they produce nuclei rapidly. Thus formation of many small crystals takes place. Probably because it causes the breaking of many nuclei from crystals already formed.
Concentration of the solution (saturation) Fairly large amounts of sugar dissolve easily in water. The higher the temperature of water, the greater the amount of sugar that will dissolve in water . Maltose and glucose are less soluble than sucrose. Hence, when syrups containing a large proportion of these sugars are used, more water must be added to dissolve them. The right conditions for rapid crystallisation is to have the syrup to heat upto the right temperature or adjust to the right concentration. The lower the temperature the smaller the size of the crystals . Gulab jamun and jalebi syrups are not supersaturated solutions hence do not crystallise.
Agitation or stirring Agitation favours the formation of finer crystals than are produced spontaneously. Stirring brings the supersaturated solution in contact with each crystal. It is important to stir crystalline candy not only until crystallisation starts, but until it is complete.
Impurities Impurities that may be deposited on the crystals reduce the growth of the crystals. The presence of glucose interferes with the crystallisation of sucrose. Another way an impurity may interfere with crystallisation is by coating the crystals. The use of fat, flour, milk, coconut, nuts, interfere with the crystal formation. For example, in making mysore pak, flour and fat are added which interfere with crystallisation.
Addition of acid An acid ingredient like cream of tartar, lemon juice or vinegar may be added to hasten the inversion of sucrose to glucose and fructose. For example, addition of citric acid to jams and jellies prevent crystallisation. In sweet pickles when mango is used crystallisation is prevented.
Boiled sugar solutions may be treated to produce either crystalline or non-crystalline candies. Crystalline candies are generally soft. If properly made, they are so smooth and creamy that the tiny sugar crystals that make up their microscopic structure cannot be felt on the tongue. The principal crystalline candies are fondant, mysore pak and coconut burfi.
Non-crystalline candies are sometimes called amorphous which means “without form”. In their preparation, by use of various techniques, crystallisation of sugar is prevented. Non-crystalline candies may be chewy, such as caramels or hard such as butter scotch, toffees and brittles.
Last modified: Tuesday, 13 December 2011, 10:51 AM