Food processing operations such as blanching, cooking, pasteurization, and sterilization involve temperature-dependent biochemical or chemical changes. The safety and quality of foods depend critically on correct temperature regimes; for example, in canning the classical problem is finding the optimum heating regime that inactivates any microorganisms while still preserving nutritional quality (avoiding overprocessing and destruction of vitamins). In water-containing foods, heat transfer is often accompanied by a significant water transfer. Thus the quality and safety of foods depend critically on the entire temperature history and the state and distribution of water in the food. Other physical properties and variables such as pressure, flow, electric fields, and water activity also critically influence processing of foods.