Candies
Candies are made of sugar (sucrose), water or other liquid and usually some interfering agent(s). Butter, milk, cocoa and corn syrup are commonly used as both crystal interfering agents and flavoring. Candy begins when the water or other liquid is supersaturated with the solute, usually sucrose. Supersaturation occurs when more sugar is present than can be dissolved at that temperature. By heating the solution above the boiling point of water the solute concentration becomes greater. A supersaturated solution is formed when this solution, after heating to a high temperature, is allowed to cool undisturbed. Upon cooling the sugar recrystallizes into several small crystals or forms one large amorphous mass. For crystallization to occur, nuclei must form and solute must be added from the solution to these nuclei. Usually these nuclei form spontaneously but sometimes are "seeded" to the cooked mixture to initiate crystallization. The size of the resulting crystals depends on the number of nuclei, rate and temperature of crystallization, agitation and impurities in the solution.

Crystallization is a complex process with many interrelated factors. The nature of the crystallizing substance is important for crystallization, although not as obvious in candy making as sucrose is almost always the substance under discussion. The rate of crystallization is the speed at which nuclei grow into crystals. This rate is dependent upon the concentration of the solute in the solution as a more concentrated (more supersaturated) syrup will crystallize more rapidly than a less concentrated syrup. At a higher temperature the rate of crystallization is slow and becomes more rapid at a lower temperature. Agitation distributes the crystal forming nuclei and hastens crystallization.

Impurities in the solution usually delay crystallization and in some cases such as caramels may prevent crystal formation. Fat and protein decrease the number and size of crystals through the interference of their masses with the orientation of the sucrose molecules. Corn syrup also has this interfering role; however, additionally it serves to enhance the solubility of sucrose and thus decreases its tendency to crystallize. Cream of tartar as an added ingredient in a candy formula serves indirectly to decrease the rate of crystallization as well as crystal size. It does this through its ability to hydrolyze sucrose into its invert sugar. This not only forms two sugars of greater solubility than sucrose, but it gives agents which enhance the solubility of sucrose.

Frozen Desserts
A supersaturated or supercooled solution forms nuclei. This process involves the uniting of atoms. Solution or liquids at the freezing point form nuclei spontaneously or by a process called seeding. Allowing a solution to stand causes the formation of nuclei in various places spontaneously. These crystals grow from these nuclei and because the number of nuclei formed are small, they grow to large sizes. Seeding is done by adding crystals of the same material to a solution to start the crystallization process. These added crystals serve as nuclei. Agitation of the solution increases the number and the rate of nuclei formation. In water crystallization the nuclei and crystallizing substance is the solvent of the system. The larger portion of reported datum have dealt with the crystallization of solute from dispersions.

The rate of crystallization is the rate the crystallizing substance becomes a solid crystal. It is determined by the time required for a drop from one temperature to another. Other components contribute to decreasing or increasing crystallizing rate. Rapid crystallization and agitation during the freezing are a must for the formation of small crystals.

Solutes decrease the freezing point or the point of crystallization of water. Thus, the greater the solute concentration, the slower the rate of crystallization. Rate of crystallization is also decreased during the solidification of water by colloids and suspensions in a mixture. Fats, milk or egg proteins or stabilizers and emulsifiers would be in this category. These stabilizers and emulsifiers help keep the ice crystals small by absorbing some of the free water to form a gel. The gel prevents the growth of large ice crystals due to its stiffness and internal structure. Their physical presence interferes with crystal growth.

In frozen dessert mixes, air is incorporated during agitation in the freezing process. The incorporation of the air causes an increase in volume of the mix. This increase in volume is called "overrun". The whipping ability of the mix is increased by the presence of nonfat dry milk solids, egg yolks and emulsifying agents. Whipped evaporated milk, beaten egg whites and whipped cream help incorporate the air in still frozen desserts. Fat decreases the percent overrun in ice creams especially when present as large fat globules or clumps. Homogenization of the fat reduces the particle size and therefore may change overrun.

The quality of frozen desserts is evaluated by the texture (mouth feel), consistency (hardness or softness) and body. A smooth, creamy texture, a consistency that is neither too hard or too soft and a body that is not too watery and compact nor too viscous and spongy when the frozen dessert starts to melt are the qualities that determine a desirable frozen dessert.

Freezing Point: Making Sherbet

Food Item	Crystal Type	Crystal Role, Development and/or Inhibition in Foods
Fondant	sugar	Fondant is a two-base system: sucrose crystals in syrup. For good crystal formation the syrup needs to be sufficiently supersaturated. The presence of acid as an interfering agent makes both the final temperature and the cooking time critical for optimum crystal size. The temperature at which agitation begins is critical for preventing formation of too large crystals. Once agitation has begun it must be constant until the end point is reached or large crystals may be formed.
Grape Juice	tartrate crystals: Ca tartrate Potassium hydrogen tartrate	In solution the K2H2 tartrate gives the juice a cloudy appearance and an acid flavor. Bulk storage at low temperatures (less than 40F) allows for precipitation of an crystals prior to packaging. Precipitation can be brought about in as little as 24 hours using rapid freezing, thawing, and filtering. Storage is in metal, wooden or cement containers with a protective coating; glass carboys or stoneware jugs. Packing is in glass bottles or specially enameled cans. Ion exchange and cold stabilization facilitate precipitation of the crystals to improve flavor and maintain clarity.
Sherbet	ice	The ice crystals give the frozen dessert its hardness. Sherbet is a two-phase system: ice crystals in syrup. In sherbets the amount of sugar is very high to counteract the acid which serves to lower temperature at which the crystals form. Sugar also acts as an interfering agent to help keep the crystal size small. Constant vigorous agitation during freezing also helps to keep crystal size small. Addition of non-fat milk solids provides another interfering agent producing small crystals and a finer product. If nonfat milk solids are used they increase the product's viscosity and favor the incorporation of air bubbles as the mix is agitated during freezing. The fruit juice causes milk solids to thicken and thus interfere with the development of large crystals. Additionally, if cold and concentrated enough the lactose may crystallize out of solution.
Shortening	polymeric alpha, beta, beta prime and intermediate	Plastic fats are a two-phase system: crystal fat surrounded by oil. Fat crystals are relatively large and the spaces between them are large. A solid, phase, of 5-35% of the volume will give a plastic fat. Small crystals rapid cooling and rapid agitation. Large crystals -slow cooling, no agitation. Melting point of fat changes with each change in type of crystal. Homogeneity causes transformation to coarse crystals.

What reaction does addition of cream of tartar have? Why?

What relationship is there between the presence of interfering agents and final cooking temperature?

If peanut brittle was made, explain how the bubbles developed in the structure.

Explain how the temperature at which a candy is beaten influences the firmness of the final product.

What does temperature tell you about sugar concentration.

In heating a sugar solution, what causes the temperature to rise above 100C?

If peanut brittle was made, explain how the bubbles developed in the structure.

Explain how the temperature at which a candy is beaten influences the firmness of the final product.

What does temperature tell you about sugar concentration.

In heating a sugar solution, what causes the temperature to rise above 100C?

What type of effect did fat have as an interfering agent?

Why does the stirring rate need to be carefully regulated at beginning of freezing?

What ingredients are used to inhibit crystals in frozen desserts?

What causes overrun? What are factors responsible for overrun?

What is the function of eggs in a French Vanilla Ice Cream?

What effect does the substitution of milk for heavy cream have on the quality of frozen dessert?

Why are egg whites sometimes added to sherbets?

Explain the difference between a sherbet and an ice.

What prevents the mousse from freezing solid?

How does temperature of beating affect crystal nuclei formation - size and amount?

What is the effect on crystal size of replacing water with cream? Indicate explanation.

What limits crystal size in a frozen dessert made without stirring.

What is the dominant crystal possibly in the following products?

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Updated: Wednesday, October 24, 2007.