Continuous Thermal Processing
The basics of thermal processing are discussed at great length in many other texts (Singh and Heldman 2001, Ibarz and Barbosa-Canovas 2003, Karel and Lund 2003, Charm 1971, among many others), so they will only be summarized here. For a given food and for a given objective (cooking, refrigerated shelf life, ambient shelf life, complete sterility), there is a time at a specified temperature that must be achieved. In a continuous process this hold time is controlled by the length of the hold tube for a specified flow rate. It is important to know the flow regime in the hold tube – whether it is laminar or turbulent – as this determines the velocity profile and thus the hold time. Many fluid foods are viscous and non-Newtonian in their flow behavior and so estimating heat transfer coefficients and pressure drops can be challenging.