Question

Sufficient head space must be allowed during filling of evaporated milk in cans to ___________

• A. avoid coagulation of curd
• B. allow for expansion and to prevent opening of seams
• C. prevent germination of spores
• D. avoid sedimentation

Hint:

To remember the role of headspace in canning:
- Too little headspace \(\rightarrow\) Thermal expansion \(\rightarrow\) High internal pressure \(\rightarrow\) Seams split or can bulges.
- Too much headspace \(\rightarrow\) Underfilled can \(\rightarrow\) Excess air can cause internal oxidation.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Evaporated milk is packaged in tinplate cans and subjected to in-container retort sterilization at temperatures of 115°C to 120°C for 15 to 20 minutes.
During this intense heating, the physical volume of the liquid milk and the air trapped inside the can expands significantly.

Step 2: Detailed Explanation:
Leaving an adequate headspace (typically 6 to 12 mm from the top of the can) is critical to maintaining container integrity during retort processing:
- As the temperature rises during sterilization, both the liquid milk and the gases in the headspace expand.
- If the can is overfilled and lacks sufficient headspace, this thermal expansion creates extremely high internal hydrostatic pressure.
- This excessive pressure can cause physical deformation of the can, such as bulged ends.
- More critically, it can stress and rupture the double seams of the can.
- This seam damage allows cooling water to leak into the can after processing, causing bacterial spoilage.
- Conversely, a proper headspace acts as a buffer zone, absorbing the volume expansion and preventing seam failures.
- During cooling, this headspace also helps create a partial vacuum inside the can, which helps preserve the product.

Step 3: Final Answer:
Sufficient headspace must be allowed to accommodate thermal expansion of the contents and prevent the opening of the can's seams during sterilization.