Although deep frying has long been recognized as one of the most popular methods restaurants can employ to cook their menu items, many operators still find themselves asking one question in particular: How hot should their oil be?
While it sounds as if there should be a simple answer, the process is more complicated than many initially recognize. In fact, there are a number of variables that affect deep-frying, including the age and condition of the oil, the amount of moisture contained in the product being cooked, how much product is being fried at a given time, the thickness and type of the food, and the type of oil being used.
But there are actions operators can take to help control the life and effectiveness of frying oil — while maintaining the optimum temperature.
Simply put, deep frying is a dehydration process in which thermal energy is conveyed through hot oil and transferred to a food product. During the process moisture in the food evaporates through steam.
If the oil temperature is too high, the improper transfer of heat can dry the food out and burn the outer layer of the item; if it is too low, the item being cooked will absorb excessive amounts of fat and become greasy.
The ideal temperature, on the other hand, should yield a food item with a crisp exterior and a moist, thoroughly cooked interior.
Typically, food products will have an ideal temperature and cooking time listed on their container. Some basic food examples and recommended temperatures include: French fries, about 350 degrees Fahrenheit; fish, around 325 degrees Fahrenheit; and donuts, about 325 degrees Fahrenheit.
Not surprisingly, though, different food products fry best in different types of oils. For example, if you want the flavor of the food to shine through, experts recommend cooking in sunflower or soy oil, which have a milder taste. If an operator is looking to impart a nutty flavor to french fries, cottonseed works well. For tortillas and other Mexican-flavored foods, corn oil is usually the way to go, experts say.
Meanwhile, there are a number of fry oil enemies that can result in oil breakdown and bring out unwanted characteristics in food. However, those can be ameliorated through good frying practices — known as “staying in the sweet spot” — according to Roger Daniels, vice president, research, development and innovation for Stratas Foods LLC. Consequently, it is in the best interest of the operators to implement a practical oil management policy based on their frying needs.
Excessive heat is one enemy of frying oil. Oil degradation reactions double for every 18 degrees Fahrenheit increase in temperature. This, however, can be addressed by maintaining a lower fryer temperature when not in use, frying foods at the minimum temperature necessary to provide the desired food quality, checking and calibrating fryers often, and storing fry oils at recommended temperature, usually 65 degrees to 75 degrees Fahrenheit.
Water is another enemy of frying oil. The process of hydrolysis can lower the smoke point and contribute to off-flavors. To help minimize this problem, Daniels recommends that operators should dry fryers thoroughly after cleaning, make certain baskets are not filled over the fryers and knock excess ice off food before frying.
Oxygen and light can drive oxidation, which also can contribute to off odors and flavors. To help lessen the impact, operators should check fryer pumps for air leaks, cover fryers when not in use and store fry oil in a sealed container.
A fourth enemy is contaminates, which also contribute to oxidation. To decrease the amount of contaminates in oil, operators should neutralize caustic cleaners and ensure that a fryer is well rinsed when cleaning, eliminate reactive metals from all oil contact surfaces, skim the oil frequently and filter daily with an active filter aid, and don't salt or fill baskets over the fryers. Breaded foods tend to be hardest on the life of an oil.
One of the biggest problems in frying, though, when oil is retained for too long. The lifetime effectiveness of cooking oil can be illustrated by a quality curve.
The curve begins at the “break-in” period — the earliest point in an oil's lifecycle. Over time and through usage, the oil gradually becomes conditioned, climbing to what is characterized as “fresh,” and eventually achieving its peak performance at the uppermost point of the curve known as “optimum.” Once past that peak, however, the oil steadily breaks down, which is characterized as “degrading” and finally “runaway.”
A fresher oil can take a higher temperature, while the longer the oil is kept the more careful an operator has to be with heat, Daniels says.
As the oil breaks down, it creates free fatty acids which, among other things, lower the smoke point and negatively impact the flavor.
As a result, Stratas recommends that operators formulate the appropriate oil management strategy. To accomplish that they need to take into account such factors as the type of food they're serving, the amount of time the oil is heated and the amount of product prepared.
There also are a number of ways to gauge when an oil should be changed. The ultimate method for oil change strategy, Daniels says, is organoleptic, which measures aroma, appearance and the taste of the food. It can be subjective, however, and requires a trained palate.
Measuring color — oil darkens as it oxidizes — through a color tube guide also is effective and works well in conjunction with sensory methods. In addition, test strips can be used to measure free fatty acids, which increase as the oil degrades. The observation of smoking and foaming also are signs that the oil is over the hill — although by the time they become apparent, it is probably too late.
Increasingly, Total Polar meters are being used to measure the degradation of frying oil. But while the meters are relatively accurate, they tend to be costly, delicate and require calibration and training.
Consequently, for operators looking to identify how hot their oil should be, it becomes readily apparent that a number of critical factors must also be taken into consideration over time. But while there is no simple answer, operators who pursue an appropriate oil management strategy and continue to work with their suppliers are likely to get the most out of their frying oil — in heating effectiveness, taste and longevity.