Temperature Control When Cooking Using Fats
It is difficult to detect overheating visually, because fat does not boil, and heated oil is always hotter than it appears. Overheating contributes to the rapid deterioration of fat through polymerization. Any egg yolks used in the coating batter also contribute to the darkening effect on the fat. Further, the increased viscosity of overheated fat results in higher fat absorption rates in the fried foods, making them greasy. One way to control the temperature of cooking fats and prevent excess absorption is to use thermostatically controlled deep-fat fryers, but it is recommended that these thermostats be checked for accuracy routinely.
While it is important not to overheat frying fats, it is equally important not to let temperatures drop too low, since this may lead to excessive fat absorption, resulting in soggy, greasy fried food. Temperatures quickly drop when large quantities of frozen food are added to hot oil. To help stabilize the temperature, the food should be added in batches so the oil will be given sufficient time to reheat to the correct temperature. It is important that the food pieces in a batch be the same size, so they finish cooking at the same time.
If temperatures are correctly controlled, the result will be a food that has a crisp, golden crust surrounding a tender, perfectly cooked center. The key in deep-fat frying is to ensure that the food’s inside is sufficiently cooked without overdoing its outside. Fried foods cook on the principle that frying temperatures convert the food’s water to steam, which then escapes, keeping the food cool and preventing it from burning and/or absorbing fat. Eventually, however, the amount of steam decreases, allowing the outside to brown. Foods left too long in the fryer after all the steam has escaped will have burned crusts and excess fat absorption.
Optimal frying temperature is 375oF (191oC), with higher temperatures (375o to 390oF/191o to 199oC) required for smaller pieces of food, and lower temperatures (350o to 365oF/177o to 185oC) for larger pieces of food. Another factor in selecting temperature is moisture content. High-moisture foods such as French fries need to be cooked at lower temperatures or the outside will turn crispy before the inside has had a chance to cook. Steam trapped by the hard crust will cause the food to become limp as it cools. Conversely, low-moisture foods need higher temperatures so they will cook quickly, leaving oil no time to enter the food. Other determinants in temperature selection are the amount of food, the length of time it is submerged in oil, the temperature of the food, the oil quality, and the food’s shape and size, porosity, and type of coating.
