Subtopic: Cold point location in conduction vs convection heated cans
Question Statement:
Which of the following statements regarding the 'slowest heating point' (cold point) in canned food sterilization is/are TRUE?
Options:
(A) In solid conduction-heating foods (e.g. corned beef, pumpkin puree), the cold point is located at the geometric center of the can
(B) In liquid convection-heating foods (e.g. clear broth, thin juices), the cold point is located on the central vertical axis, approximately one-third to one-fifth of the height from the can bottom
(C) Thermal process lethality calculations must be based strictly on the time-temperature history of the cold point
(D) In broken-heating foods, convection persists uniformly until the end of the cooling cycle
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. Conduction heating is symmetrical, locating cold point at geometric center (A is true).
2. Convective boundary layers rise along warm side walls and plunge down the center, depressing cold point to near the bottom ($1/3$ to $1/5$ height) (B is true).
3. Ensuring commercial sterility at the coldest point guarantees adequate sterility throughout the remainder of the container (C is true).
4. In broken heating, starch gelatinizes or pectin dissolves mid-cycle, transitioning flow from rapid convection to slow conduction (D is false).