Thickening agent

Thickening agents, or thickeners, are substances which, when added to an aqueous mixture, increase its viscosity without substantially modifying its other properties, such as taste. They provide body, increase stability, and improve suspension of added ingredients. Thickening agents are often used as food additives and in cosmetics and personal hygiene products.

Food

Food thickeners frequently are based on either polysaccharides (starches, vegetable gums, and pectin), or proteins. A flavourless powdered starch used for this purpose is a fecula (from the Latin faecula, diminutive of faex meaning "dregs"). This category includes arrowroot, cornstarch, katakuri starch, potato starch, sago, and tapioca. Vegetable gums used as food thickeners include alginin, guar gum, locust bean gum, and xanthan gum. Proteins used as food thickeners include agar, carrageenan, collagen, egg whites, furcellaran, gelatin.

The relative merits of these thickeners depend on numerous factors, including their chemistry. For example, for acidic foods, arrowroot is a better choice than cornstarch, which loses thickening potency in acidic mixtures. At (acidic) pH levels below 4.5, guar gum has sharply reduced aqueous solubility, thus also reducing its thickening capability. If the food is to be frozen, tapioca or arrowroot are preferable over cornstarch, which becomes spongy when frozen.

Many other food ingredients are used as thickeners, usually in the final stages of preparation of specific foods. These thickeners have a flavor and are not markedly stable, thus are not suitable for general use. However, they are very convenient and effective, and hence are widely used. Flour is often used for thickening gravies, gumbos, and stews. It must be cooked in thoroughly to avoid the taint of uncooked flour. Roux, a mixture of flour and fat, made into a paste before the liquid is added, is used for gravies, sauces and stews. Cereal grains (oatmeal, couscous, farina, etc.) are used to thicken soups. Yogurt is popular in Eastern Europe and Middle East for thickening soups. Soups can also be thickened by adding grated starchy vegetables before cooking, though these will add their own flavour. Tomato puree also adds thickness as well as flavour. Egg yolks have rich flavor and offer a velvety smooth texture but can prove to be difficult to use. Other thickeners used by cooks are nuts (including rehan) or glaces made of meat or fish.

When using a thickening agent, care must be taken not to overcook the food. Some starches lose their thickening quality when cooked for too long or at too high a temperature, and thickened food may burn more easily during cooking. As an alternative to adding more thickener, recipes may call for reduction of the food's water content by lengthy simmering. When cooking, it is generally better to add thickener cautiously; if over-thickened, more water may be added but loss of flavour and texture may result.

Cosmetics

Thickening agents used in cosmetics or personal hygiene products include polyethylene glycol, synthetic polymers such as carbomer (a trade name for polyacrylic acid) and vegetable gums. Some thickening agents may also function as stabilizers when they are used to maintain the stability of an emulsion. Some emollients, such as petroleum jelly and various waxes may also function as thickening agents in an emulsion.

Incendiary devices

Many fuels used in incendiary devices require thickening for increased performance. Aluminium salts of fatty acids are frequently used. Some formulations (e.g. Napalm-B) use polymeric thickeners, namely polystyrene. Thickened pyrophoric agent, a pyrophoric variant to napalm, is a triethylaluminium thickened with polyisobutylene.

See also

Mucilage

External links

• Cook's Thesaurus: Thickeners