In cooking, thickening is the process of increasing the viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 of a liquid either by reduction

Reduction (cooking)

In cooking, reduction is the process of thickening and intensifying the flavor of a liquid mixture such as a soup, sauce, wine, or juice by boiling....

, or by the addition of a thickening agent

Thickening agent

Thickening agents, or thickeners, is the term applied to substances which increase the viscosity of a solution or liquid/solid mixture without substantially modifying its other properties; although most frequently applied to foods where the target property is taste, the term also is applicable to...

, typically containing starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

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Dessert

Dessert

In cultures around the world, dessert is a course that typically comes at the end of a meal, usually consisting of sweet food. The word comes from the French language as dessert and this from Old French desservir, "to clear the table" and "to serve." Common Western desserts include cakes, biscuits,...

s are often thickened with sago

Sago

Sago is a starch extracted in the spongy center or pith, of various tropical palm stems, Metroxylon sagu. It is a major staple food for the lowland peoples of New Guinea and the Moluccas, where it is called saksak and sagu. A type of flour, called sago flour, is made from sago. The largest supply...

, tapioca

Tapioca

Tapioca is a starch extracted Manihot esculenta. This species, native to the Amazon, Brazil, Colombia, Venezuela, Cuba, Puerto Rico, Haiti, the Dominican Republic, Honduras, and most of the West Indies, is now cultivated worldwide and has many names, including cassava, manioc, aipim,...

, gelatin

Gelatin

Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...

 or a gelatine substitute such as agar

Agar

Agar or agar-agar is a gelatinous substance derived from a polysaccharide that accumulates in the cell walls of agarophyte red algae. Throughout history into modern times, agar has been chiefly used as an ingredient in desserts throughout Asia and also as a solid substrate to contain culture medium...

. Soup

Soup

Soup is a generally warm food that is made by combining ingredients such as meat and vegetables with stock, juice, water, or another liquid. Hot soups are additionally characterized by boiling solid ingredients in liquids in a pot until the flavors are extracted, forming a broth.Traditionally,...

s, sauce

Sauce

In cooking, a sauce is liquid, creaming or semi-solid food served on or used in preparing other foods. Sauces are not normally consumed by themselves; they add flavor, moisture, and visual appeal to another dish. Sauce is a French word taken from the Latin salsus, meaning salted...

s and stew

Stew

A stew is a combination of solid food ingredients that have been cooked in liquid and served in the resultant gravy. Ingredients in a stew can include any combination of vegetables , meat, especially tougher meats suitable for slow-cooking, such as beef. Poultry, sausages, and seafood are also used...

s are more often thickened with a starchy product like cornstarch

Cornstarch

Corn starch, cornstarch, cornflour or maize starch is the starch of the corn grain obtained from the endosperm of the corn kernel.-History:...

, arrowroot

Arrowroot

Arrowroot, or obedience plant , Bermuda arrowroot, araru, ararao, is a large perennial herb found in rainforest habitats...

 or wheat

Wheat

Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...

 flour

Flour

Flour is a powder which is made by grinding cereal grains, other seeds or roots . It is the main ingredient of bread, which is a staple food for many cultures, making the availability of adequate supplies of flour a major economic and political issue at various times throughout history...

, or a fat and flour mixture such as roux

Roux

Roux is a cooked mixture of wheat flour and fat, traditionally butter. It is the thickening agent of three of the mother sauces of classical French cooking: sauce béchamel, sauce velouté and sauce espagnole. Clarified butter, vegetable oils, or lard are commonly used fats. It is used as a...

 or beurre manié

Beurre manié

Beurre manié is a dough, consisting of equal parts of soft butter and flour, used to thicken soups and sauces. By kneading the flour and butter together, the flour particles are coated in butter...

. More rarely, savoury dishes may be thickened with blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

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