Perhaps the biggest concern with any kind of filtration system is blinding of the filter. Industrial operations often use indexing paper filters to continuously remove particulates from oil. A stationary system could blind very quickly, especially in an operation producing battered products, hence the indexing or moving paper. The type of product being fried has a direct influence on the potential for blinding a filter. By-products of frying that are slimy, pasty, or sticky will have a greater potential for blinding a filter. Examples of these products are meats, fish, and kettle-style potato chips. One might ask, “Why kettle style?” They are not rinsed prior to frying, so the potato starch ends up in the oil. Items like fried corn products, such as tortilla chips and breaded products, yield grainy by-products that are less likely to blind a filter and, in fact, can even build a filter cake on the filter medium.
Selecting an Oil Filtration or Treatment System
There are many different products available to the fryer operator at both the foodservice/restaurant and industrial levels. Each and every fryer operator will probably utilize a passive filtration system of some sort, but the question is, “Would installing an active system be beneficial or not?” In industrial frying, there are many different systems available to remove particulates, some of which are not filters at all. There are drag bars that remove particulates that settle to the bottom of the fryer and are then dragged from the fryer by the bar. Some processors use centrifugal separators. Systems that filter oil include catch boxes, stainless steel screens, rotary drums, stainless steel baskets, continuous belt filters, bag filters, and filter presses. Heat and Control is one of the main producers of fryers and frying systems.
There are also active systems currently in use by industrial frying operations. Most of these are designed to treat oil at the end of the day’s production. One example is a system where the used oil is mixed with an active treatment powder and allowed to react with the oil in a mix tank. The treated oil is then filtered to remove the powder and transferred to a holding tank or back into the fryer to be used in the future. The Dallas Group provides powders and the treatment system. Other systems, such as those from Filtercorp, utilize filter pads impregnated with active ingredients. The oil from the fryer is slipstreamed from the fryer and pumped to a filter vessel and through the filter pads on a continuous, real-time basis, before it is returned to the fryer or a holding tank. Filtering/treating oil continuously would require a pre-filter to remove suspended solids to prevent blinding of the system.
Today, a significant percentage of the fryers used in restaurant or foodservice operations are manufactured with a built-in filter apparatus but may also have working relationships with one or more suppliers of filtration products and services. There are also fryers that do not come with a built-in filter. In these fryers, an operator must utilize a portable filter that can be hooked up to the fryer at the end of the work day. Years ago, some operators used cone filters. The user would place a filter in the metal cone, and the fryer operator had to ladle oil into the cone so it could flow though the filter via gravity. These units posed a significant risk to workers handling the hot oil, so it is good that they have been phased out.
Both active and passive systems are used in foodservice and restaurant operations. The most common passive system is filter paper, which simply removes suspended solids from oil. Active systems include impregnated pads or papers, paper and powder, and powder. With paper and powder systems, the active treatment product is sprinkled on paper, and the oil is filtered over the powder and through the paper. In some cases, the powder is added to the oil and filtered out, but this type of system is losing favor as there are concerns about adulterating the oil and potentially the food.