AbstractThe chemical and physical changes that occur in frying facts during use and their significance to fat life and to finished product quality are reviewed. The more commonly used quality control tests for monitoring these changes are examined as is their applicability to food service institutions and food processors. The advantages and disadvantages of these tests and possible modifications to improve their ease for on‐the‐spot testing are discussed. Chemical tests such as free fatty acids (FFA), thiobarbituric acid (TBA) tests and peroxide value (PV) are available to those operations with laboratory facilities, whereas sensory and physical tests, including foam height, color, smoking, viscosity, odor and product flavor, are generally relied on by most food service facilities for on‐the‐spot assessment. The reliability of these tests, however, depends on the source and type of frying fat, the food being fried, and, in the case of the sensory and physical tests, on the skill and experience of the operator. Studies completed recently in this laboratory found a high correlation between polar compounds or FFA and length of frying time which suggests that either could predict oil abuse accurately. Recent adaptations which could facilitate on‐the‐spot testing by semi‐skilled personnel (including a spot test for FFA and an instrument capable of monitoring the change in dielectric properties of an oil during frying) will be examined. Regardless of the quality control test used, the question remains of specifying reliable cutoff levels which can be related to the health and sensory constraints. This problem is also discussed.