The food processing industry uses various techniques to transform food ingredients into different forms for consumers. Separation techniques may be used to remove skins from fruits, water from juices, or whey from cheese. Each separation technique is customized to the amount of waste that needs to be removed, and the resiliency of the food product being processed.
This separation technique is usually used on a liquid. It can be used to separate out solids or to separate out one or more liquids with different densities than the main liquid. For instance; it is used to separate vegetable oils from other liquid products of the crushing process, or to clarify beverages that have developed a cloudy appearance because of dissolved solids. The process of centrifugation involves spinning a container, with the food inside it, in circles at a very high rate of speed. One of the ingredients moves to the outside of the spinning radius, and the centrifugation machine has nozzles or separated pans to collect the material that spins out.
Membrane filtration involves forcing a solution through a porous membrane. The membrane is usually designed to keep out substances with a large molecular size. For instance, skimmed milk is filtered through a membrane designed to exclude bacteria-sized objects. Reverse osmosis, which removes water from liquids, is also considered to be a membrane filtration method. This is sometimes used to concentrate juices without heating them, which protects their flavor and nutritional profile.
Many machines are designed to remove solid food products from their associated waste. For instance; there are machines that pull the husks off ears of corn, and machines that remove feathers from chickens before they are butchered. Some foods that are mechanically separated are also processed with chemicals to make it easier to remove the waste from the food product. This is sometimes done to fruits or nuts before they are peeled. Most of these machines are specially designed for the size and texture of the food product they are used to process.
Extraction removes some food compounds that are closely co-mingled with other materials. For instance; it is used to remove sugar from sugar cane and caffeine from coffee beans to make decaffeinated coffee. Extraction involves soaking the food in a solvent that dissolves the food product or food waste, then filtering that solvent out or using centrifugation to separate it.
References and ResourcesNational Food Research Institute: Reaction and Separation Engineering Laboratory
Hyfoma: Separation Techniques
Fisher College of Business: Separation Techniques for Produce Processing
Foodprocessing Technology; The Lowdown on Nanofiltration; Frances Penwill-Cook; Sept 2010