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Pressure frying is a cooking method that requires special equipment designed to heat oil and food together in a pressurized environment controlled by the cook and the equipment. The food that results from pressure frying tends to have a crisp exterior from the hot oil and retain moisture inside, because the pressure prevents the water or other liquids in the food from boiling and turning to steam. For the most part, pressure frying is performed mostly in commercial or industrial kitchens, because it requires special equipment that can be very expensive or unavailable to non-commercial buyers. One large benefit from using pressure frying is that less time and oil are required to cook the food, sometimes reducing the amount necessary by as much as half. Despite some anecdotes and failed commercial products, pressure frying cannot be safely performed in a standard pressure cooker.
The process of pressure frying begins with oil that is heated in a pressure fryer until it is at the desired temperature. Next, the food that will be cooked is added to the oil and allowed to fry briefly so the outside crisps and the oil has a moment to return to the proper temperature. The lid to the fryer is then locked on to create a pressure seal, and the cooking process continues under pressure until the food is done.
One reason why pressure frying works differently than other cooking methods has to do with the pressure, which is lower than that used in a standard pressure cooker. Under pressure, the boiling point of water is increased so liquids inside the food will have to become much hotter to boil. When the temperature of the oil is moderated under pressure, the temperature of the outer surface of the food is increased to the point where moisture boils and evaporates, leaving a crispy crust. The interior temperature of the food, however, is never allowed to rise high enough for moisture to evaporate, leaving food moist on the inside.
In commercial restaurants, pressure frying is able to make food that is crisp on the outside while being fully cooked and moist on the inside. Additionally, the food cooks faster than standard frying or grilling and uses less cooking fat and energy over time. Several restaurant chains rely on pressure fryers to provide for customers distinctive food products that are difficult or impossible to reproduce accurately at home.
Since the original use of pressure fryers in commercial restaurants, home cooks have attempted to reproduce the results using standard pressure cookers. It is important to note that it is not safe to attempt to fry food in oil under pressure in a unit that is not specifically designed to do so. A professional pressure fryer is not only re-enforced to prevent catastrophic accidents from occurring, but it also operates at a lower level of pressure than a standard pressure cooker does. One major reason why a regular pressure cooker cannot be used as a pressure fryer is because the hot oil can destroy important parts and regulators inside the cooker, causing it to malfunction and potentially send burning oil flying through the air.
The fast food chain Kentucky Fried Chicken (KFC) owes its very existence to pressure frying. Traditional fried chicken could take twenty minutes or longer to cook, but Colonel Sanders figured out that chicken placed in a pressure fryer would cook in half that time. The finished fried chicken would also be juicier and crisper than traditional chicken fried in hot oil alone. KFC still uses pressure fryers to produce large batches of chicken for fast food service.