The two most popular types of stocks are white stock and brown stock. These classifications refer, in general, to the contents and preparation methods of the stock, not necessarily to its color. A white stock made with beef and beef bones will be slightly brown in color; nonetheless, it is considered a white stock due to the method of preparation.
White stock is made with white meat or beef, veal bones, chicken carcasses and aromatic vegetables. The bones, or meat, are put in cold liquid and slowly brought to a boil. The mirepoix (a flavoring base of diced vegetables and occasionally pork fat) is sweated in a suitable fat and, before any color develops, is added to the liquid. The mixture is then reduced to a simmer to finish cooking. This stock serves as a base for white sauce, blanquettes, fricassee and poached dishes.
Brown stock is made with beef, veal and poultry meat and bones. The bones are roasted until golden in color. The mirepoix is added when the bones are three-quarters roasted. Tomato product also can be added at this time. When the bones and mirepoix are golden in color, cold liquid is added and the mixture is slowly heated to boiling. Then the heat is reduced and the stock simmers for a period of hours. This stock serves as the base for brown sauces and gravies, braised dishes and meat glazes.
Some important basic principles to follow for quality stock preparation:
Always use cold liquid. Hot liquids seal the surfaces of stock ingredients and impede flavor development. Also, the protein complex albumin (present in bones) that promotes natural clarification is soluble in cold liquid only.
Cook over low heat. Bringing stock slowly to a boil gives the albumin sufficient time to pass into the solution. As its proteins coagulate, they attract stray particles in the stock. The slower the application of heat, the better the removal of cloudiness from the stock.
Skim the stock. Fat and scum will collect on the surface of the stock during the early stages of cooking; these particles must be removed carefully.
Skim properly. The stock should have a slight roll when cooking. If the heat is too high, the turbulence will be too great. The heavy rolling action of a high boil will break up the scum and fat, making it difficult to skim the stock. The fast rolling action also does not allow the albumin to gather the fine particles, resulting in a cloudy end product.
If the heat is too low, there is little or no movement in the stock. When movement is insufficient, particles settle at the bottom of the stock pot and burn, creating an undesirable flavor.