Question

In conduction type of heating packs of a can the slowest heating point lies at

• A. Geometric axis of a can
• B. Geometric center of a can
• C. Near to the seam
• D. Below the lid

Hint:

To ensure commercial sterility, the thermocouple used during heat penetration trials must be inserted precisely into the cold point (geometric center for conduction-type packs).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Establishing thermal process safety (retorting) requires identifying the "cold point" or slowest heating point inside the can to ensure complete destruction of bacterial spores.

Step 2: Detailed Explanation:
- Conduction heating: Occurs in solid or highly viscous food packs (such as solid-pack tuna or salmon). Heat transfer is slow, proceeding molecule-to-molecule from the hot outside metal walls inward.
- For a cylindrical can, this inward heat front reaches the center last.
- Consequently, the slowest heating point (cold point) lies exactly at the geometric center of the can.
- Note: In convection-heating liquid packs, the cold point is located lower down along the central vertical axis (about \(1/10^{th}\) to \(1/3^{rd}\) from the bottom).

Step 3: Final Answer:
The slowest heating point in conduction-heating packs lies at the geometric center of the can, which corresponds to option (B).