THE LETHALITY‐FOURIER NUMBER METHOD. HEATING RATE VARIATIONS AND LETHALITY CONFIDENCE INTERVALS FOR FORCED‐CONVECTION HEATED FOODS IN CONTAINERS

Abstract

ABSTRACTHeat transfer and lethality in foods heated by force‐convection in agitated, reel‐type retorts (Steritort) were investigated. Equations describing the temperature profile at any position in the food were developed and experimentally verified for fluids and fluids with particles. For both types of food, the temperature profiles are a function of the heat transfer coefficient (h) at the inside surface of the container (the fluid container interface). For foods with particulate pieces, the temperature profiles, in both the fluid and the particle, are also a function of the heat transfer coefficient (hp) at the fluid particle interface. Empirical models are presented correlating both heat transfer coefficients (h or hp) with system parameters.Equations describing the temperature profile at the coldest point in the food (i.e. the point receiving least lethal treatment) were used in a modified form of the lethality‐Fourier number equation (Lenz and Lund 1977a) to calculate lethality. This method of calculating lethality agreed with lethalities calculated by the Improved General Method.Confidence intervals for lethality for forced‐convection heated products were determined using the Monte Carlo procedure described in Lenz and Lund (1977b). The 95% confidence intervals for the lethality ranged from 20–60% of the median value of the lethality depending on process conditions. The fluid/particle interface heat transfer coefficient (hp) had a significant effect on the lethality distributions.