Thickening agents give body, consistency, taste and nutrition when used in foods. Flavored liquids are thickened and converted into soups, sauces, gravies, and curries etc. Thickening agents are used to transform the stocks into sauces. There are various types of thickening agents used in kitchens today:
- Starches
- Flour
- Roux
- Beurre Manie
- Fruit and Vegetable Pureé
- Egg yolk
- Cream
- Butter
- Blood
Different kinds of Thickening Agents in Cooking
Starches
Starchy roots and vegetables and cereals like rice are the oldest thickeners for sauces. They are efficient, inexpensive and can be used without imparting flavor of their own. Starches should be combined with liquid and boiled so that they gelatinize and add thickness to the food. Cornstarch, arrowroot starch and potato starch are instant starches that produce shiny sauces. Flour contains protein which gives a matty appearance to the sauces. Cornstarch is used at the last minute for the thickening of the sauces and gravies. When cooked for long time then it looses its thickening power. Cornstarch is first mixed in cold water and then gradually added to boiling liquids to thicken them. Arrowroot is the best of the purified starches because it remains stable even after prolonged cooking. It is used the same way as cornstarch. Potato starch is one of the first starches to be used in French cooking; it has never been popular as a sauce thickener. It is used the same way as the cornstarch and tends to break down after prolonged exposure to heat.
Flour
Flour is the most popular thickener for the sauces. It can be used in several ways. Flour binds with food and holds it in suspension throughout the liquid. Flour may be used as – 1. Roux is equal quantities of flour and butter cooked together to various degrees. Cooking it enhances flavor of the flour and eliminates lumps. Due to impurities of butter and proteins in flours, sauces thickened with roux are usually skimmed while simmering to remove impurities. There are three types of roux:
a. White roux, prepared by cooking flour and butter over low heat and stirring constantly with a whisk till it becomes sandy in texture. Color of the flour does not change. It is used for Béchamel sauce and cream soups.
b.Blond roux, made the same way as white roux but cooked longer, till it turns blond in color. After the cooking mixture of butter and flour becomes sandy, further cooking combines them again so that it becomes smooth and pale golden in color. It is used for making velouté sauce and velouté soups
c. Brown roux, made by cooking flour and fat gently for a long time, stirring constantly with a whisk, till it turns dark brown. Since the smoking point of butter is low, these roux are best made with animal fats. It is used for brown sauce and meat gravies. Care should be taken that the roux is brown and not black as black color brings about bitterness in the liquids that it is used for thickening.
Beurre Manie
Beurre Manie is equal quantities of butter and flour kneaded together. It differs from roux because it is not cooked. Small balls of beurre manie are added at the end of the cooking to simmering stews and sauces when their consistency is thin, whisking continuously to avoid lumps. Foods in which beurre manie has been added must be cooked to remove the raw flavor of flour.
Pureé
Pureé of meat, fish, poultry, fruit or vegetable is used in thickening sauces and soups. Pureé soups are the best example. Pureé is made by cooking the food till it becomes soft and then mashing and passing them through a strainer. Liquids thickened by pureé of non starchy foods are not stable. Their liquids tend to separate from the solids upon storing. Adding a little roux to such liquids binds them well.
Egg Yolk
They act as a base for emulsified sauces such as mayonnaise and hollandaise. Equal quantities of egg yolk and cream whisked together, known as liaison, is used to thicken and finish cooking liquids. This adds creaminess to the dish. Egg yolks also combine with air when used for sabayon sauce (cooked while being whisked with other liquids on a double boiler). Sauces containing egg yolks should not be boiled or they will become lumpy due to coagulation of the yolks. Egg yolks are also used for thickening of custards by adding boiling milk, etc. gradually to them beating continuously and then cooking then over a double boiler.
Cream
Soups and sauces may be thickened slightly by adding cream. Care should be taken that cream is not cooked for long or it may separate. Foods in which cream is being used as a thickener should not be high in acid content. Cream used with egg yolk, butter, flour and roux gives a better result.
Butter
It acts as an emulsifier in Hollandaise. Butter sauces are popular for their sheen and flavor. Cold butter is used in thickening cold sauces like chaud froid. Butter also acts as a binding agent for cold dishes such as pâtés and forcemeats, as do aspic and gelatin.
Blood
Blood is used in cooking to finish sauces of braised or roasted game. Blood not only deepens color of the sauce, but also acts as a thickener. The blood used must be fresh. It may be mixed with a little vinegar to avoid coagulation, if required to be used later. The most common dish thickened so is Jugged hare.