Using a commercially prepared hydrogenated lard and heating methods simulating those currently employed in commercial fryers, it was found that the rate of fat deterioration varied inversely with the temp of the heating element. This has been attributed to differences in the rate and duration of convection circulation, a measure of the amt of fat‐air contact, and therefore, thermal oxidation. When element temp were increased from 900舑2400F, while thermostatically maintaining the fat temp at 375F, it was found that the rate of convection circulation increased while the duration of convection circulation decreased, and it is postulated that the overall effect of increasing element temp is one of decreasing the total amt of fat contact with the air.It was also demonstrated that mechanical circulation of fat, as required in an externally heated fat system, significantly increased that rate of fat deterioration when compared to fat heated by conventional direct gas‐heat, if both were heated and maintained at 375F for identical periods of time.
The extent of the thermal oxidative change in commercial frying fats as measured by the amount of non-urea addueting fatty acids formed in the fat and the viscosity of the fat was compared. A direct and highly significant relationship was found. The relationship was found to be dependent upon the source and processing of the fat as well as the conditions of use. FEBRUARY 1966 ROCK AND ROTH: PROPERTIES OF FRYING FAT. I
The effect of heating fats in air and the effect of heating fats in an inert atmosphere were compared, and the relationship of air to changes in the frying characteristics of fat studied. The frying characteristics of a fat did not change to an extent that is commercially significant even after 48 hr heating at 375F in the absence of air; fats heated under identical conditions but in the presence of air, changed radically. It was found, also, that fat which had changed appreciably in frying characteristics when heated in air did not continue to change significantly when heated further under nitrogen. Hence, presence of oxygen was shown to be a necessary condition for the deterioration of the frying qualities of fat at frying temp. Rate of change of the frying characteristics was found to be directly proportional to the degree of exposure of fat surface to the oxygen.
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