IGNITION CHARACTERISTICS OF SPRAY-DRIED MILK PRODUCT POWDERS IN OVEN TESTS

A range of seven spray-dried milk product powders, commercially manufactured in Ireland, is tested for minimum ignition temperature (MIT) in an oven (all-round heating). Samples are tested as cubes with side dimensions of 25, 38, 51, 76 and 102 mm. The relationship obtained between MIT (T) and r, which is half the characteristic dimension of the sample (cube side), is given, with the coefficient of correlation obtained. In all cases, MIT decreases with increasing sample size and the equation In (delta(c)T2/r2) = M - N/T is found to describe the relationship accurately when using modified values of delta(c) for each cube size. The value of the constant, N, in each case and its relationships with the percentage fat content, total unsaturation of the powders and percentage protein content are examined Excellent correlation is found for N as a joint function of percentage of fat and percentage of protein.