A deep fryer (also known as a frier, deep fat fryer or fryolator) is a kitchen appliance used for deep frying.
While commonly used in commercial kitchens, household models are available and have become common.
Modern fryers feature a basket to raise food clear of the oil when cooking is finished. Fryers often come with features such as timers with an audible alarm, automatic devices to raise and lower the basket into the oil, measures to prevent food crumbs from becoming over cooked, ventilation systems to reduce frying odors, oil filters to extend the usable life of the oil, and mechanical or electronic temperature controls. Deep fryers are used for cooking many fast foods, and making them crisp.
The modern commercial fryer boasts improved energy efficiency which is due in part to better heat transfer systems. Commercial fryers with infrared heating or convection heating are efficient, but often expensive. The most common fryer models are electric and gas.
Electric restaurant fryers are popular in counter top models because of their mobility. They lose a little less heat than gas fryers because their heating elements are immersed in the oil, and they have a faster temperature recovery time between frying cycles. Gas fryers heat up more quickly and to a higher cooking temperature than electric fryers. Gas fryers can be powered by either natural gas or propane, both of which are generally less expensive energy sources than electricity. This makes gas power especially popular in floor model fryers.
Commercial fryers are generally available in mild steel or stainless steel. Stainless steel is less likely to corrode or stain than mild steel. Mild steel also expands under heat which may damage the welds over time. Because of this, stainless steel fryers often come with a much better warranty than mild steel fryers.
Fryers are available with a variety of fry pot styles. Some commercial fryers have a “cold zone” at the bottom of the fry pot. This is where larger food particles sink and the lower temperature keeps them from burning and tainting the oil. A tube-style fry pot has a large cold zone because the tubes are slightly above the bottom of the vat, leaving generous space for cooler oil and crumbs. This is particularly useful for cooking heavily breaded foods (such as a blooming onion). A tube-style fry pot is more difficult to clean than an open fry pot, but the tubes allow easy access to the heat source. Tube fryers are often a little less expensive than their open fry pot counterparts. Open fry pots have an external heat source, which makes them easier to clean and affords better access to the oil, but they generally offer a smaller cold zone, so food particles that sink could scorch and pollute the flavor of the oil. However, these fryers work very well for lightly breaded foods. Flat-bottomed restaurant fryers-another type of open frypot fryer-can also be difficult to clean and have no cold zone, but they are highly effective for frying dough (such as donuts or funnel cakes). Flat-bottom fryer pots may also be used with a batter trapping insert that keeps loose batter from quickly scorching on the bottom where heat is normally applied. A batter trap can also help keep loose batter from being stirred up in the oil and adhering to subsequent batches of food in order to make foods taste better and the cooking oil lasts longer.
Some domestic fryers incorporate an angled motorized rotary basket that circulates its contents through the hot oil. This design reduces the amount of oil required to roughly half that needed by a more traditionally designed fryer. Domestic fryers are generally much smaller than their commercial counterparts, and typically have a capacity of between two and four liters.
Many of the new fryer models include electronic temperature controls. These computerized controls save energy by constantly sensing and adjusting the temperature of the oil. A high quality thermostat can stay within a 7.2 ˚C range of a desired temperature, assuring accurate cook times. Safety thermostats that automatically cut the power if the oil reaches dangerous temperatures help prevent oil fires.
An oil filtration system, chemical treatment, or diatomaceous earth powder all help remove tiny food particles that are not always visible. Using these systems doubles the life of the oil. Oil filtration systems can sometimes be purchased as an enclosed part of the fryer to avoid involving employees in the somewhat dangerous process of filtering the oil with an exterior system. Many restaurants use a portable oil filtration system to transport waste oil to a disposal area. However, even old oil is not completely useless. There are ways (involving other chemicals and machinery) to “recycle” old oil as biodiesel that can power diesel vehicles.
Restaurant fryers are available with a wide array of accessories and options. There are countertop models, single floor models, and “fryer batteries” with multiple floor fryers, a filtration system, and holding stations all built together as one large floor fryer system. Individual fryers may have one or more tanks. Commercial floor-model fryers can be fitted with casters for easier maintenance and cleanup. Fry baskets also come in various shapes and sizes, from taco salad bowls to onion loaf baskets, with or without heat resistant handles.
Industrial enterprises producing deep-fried snack foods such as potato chips or pre-fried French fried potatoes use automated frying systems that consist mainly of the actual frying pan, a tube type heat exchanger to heat the frying oil, a filter, a circulation pump, a banana tank for fresh oil and the automation system, most often a PLC. As the product leaving the fryer contains a percentage of oil (in potato chips approx. 35%) there is a constant flow of fresh oil into the system. Sensors for the temperature of the oil, the oil level, different pressures in the system and other parameters are used as input for the PLC.
Naturally, a malfunctioning and/or misused deep fryer poses a serious fire risk, especially with gas-powered deep fryers. Furthermore, putting water on oil fires will cause a fire boilover and aggravate the situation. There are special fire extinguishers and hood-based fire suppression systems for food oil fires, often using alkaline chemicals such as potassium citrate and potassium acetate that react with the oils, trap the steam and vapors, and thus suppress the fire by saponification.
Domestic fryers often include a safety cut-out in case of overheating, for example if not enough oil is used or the fryer is switched on whilst empty. A reset button is included on most of these fryers to reset the safety device once the unit has cooled down; if a reset button is not included the fryer may need repairing if the safety device activates.
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