The Hospitality Guru (cooking) Back to Basics: Other Thickening Agents
EGG BASED THICKENERS
There are three egg based thickeners commonly used in cookery. Egg yolk is not a strong thickening agent and is primarily used to enrich and add smoothness of texture to a sauce or soup, or as an emulsifying agent.
Egg yolk and cream liaison
A liaison consists of a well whisked mixture of egg yolks and cream which is used to slightly thicken sauces and soups. Egg yolks thicken by coagulation of their proteins when heated. The temperature at which coagulation occurs will vary according to the liquids being thickened, but usually occurs between the range of 80-88C degrees. If the temperature increases above this range, the yolk will curdle.
When curdling occurs, the egg protein hardens, shrinks and separates from the liquid in the yolk and forms into lumps.
Therefore, the liquid to which the liaison is added must not be heated over 88C degrees. Dishes with a liaison are unsuitable for reconstitution.
A sabayon consists of egg yolk and a liquid which thickens by the process of emulsification. An emulsion is a mixture of two liquids which will not normally mix together, for example, oil and water. To mix them, they must be either forced together, for example, by vigorous beating, or be held together by a third ingredient called the emulsifying agent.
Egg yolk is an emulsifying agent. It is important to avoid breaking the emulsion (where the ingredient separate) or to allow curdling. Egg emulsions are stable emulsions. That means if the correct procedure is followed, the ingredients will not easily separate.
A sabayon is used in the production of warm emulsion sauces and some sweet products like zabaglione.
Egg yolks are used to thicken sweet and savoury custards.
OTHER THICKENING AGENTS
Blood is a good thickening agent and works in a similar way to egg yolk. It may be used to thicken traditional dishes like jugged hare and black pudding sausages. It is rarely used in modern cookery. In Australia, because of health regulations, the use of blood as a thickening agent is illegal unless a permit is obtained.
Bread is rarely used as a thickening agent because of its coarse texture. It is used to make a bread sauce or bread soup.
Purees and grains
Fruits and vegetable purees and grains are mainly used for the thickening of soups and sauces. For example, lobster bisque may be thickened with rice, scotch broth is thickened with barley and potato soup is thickened by pureeing the potatoes