Food Frying

4Chemistry of the Frying Medium

4.1 Frying Medium

The frying medium is an essential part of the frying process. Foods are partially or completely immersed and held in the frying medium at high temperature. The chemical nature of the frying medium is exclusively lipid. Lipids used as frying medium are classed as either fats or oils, depending on their physical properties. They are obtained from plant seeds known as oilseeds, nuts, and animal tissues, and are extracted using a variety of techniques. The overall process of extraction usually consists in several operational units working consecutively to produce the final product. These units include rendering or extraction, degumming, chemical and physical refining, bleaching, adsorption, hydrogenation, deodorization, and crystallization. One or more of these units may be avoided or repeated in order to obtain the frying lipid of choice, keeping in view the efficient and economic quality of the product.

The production of frying medium from animal tissues starts with the heating of the fatty tissues, in a process known as rendering. Heating solidifies the protein contents of the tissues and releases lipids. The rendering process can take two forms: dry and wet rendering. Dry rendering produces a product free of moisture, with a relatively dark colour and a cooked flavour. The end product may be used as such, or it can be processed further for physical or chemical refining. Wet rendering involves the cooking of tissues by high‐pressure ...