When shortening is filtered, suspended food particles are strained out from the hot shortening, by forcing the mixture through a porous barrier. Filtering shortening can be a chemical process, a mechanical process, or a combination of both. In chemical filtering, absorbent powder soaks up the by-products of frying. In mechanical filtering, old shortening is pumped through a straining and absorption system. Straining removes charred particles, and absorption reduces the multiplication rate of free fatty acids.
Some fryers have a built-in system that is a combination of both chemical and mechanical filtering.
This system is easier, safer and more efficient because it makes it easier to filter shortening more often. If a filtering system is not built-in, a portable filtering unit can be rolled over to the fryer. Regardless of the method, filtering shortening is of major importance in increasing shortening life. The frequency of filtering is determined by volume of frying. Daily filtering is necessary in high volume operations or in operations that cook breaded product.