Canned dairy/foods — can swelling and gas defects: Swelling (bulging) of hermetically sealed cans is caused primarily by which group of microorganisms?

Introduction / Context:
Swelling of cans is a critical food safety and quality signal. It typically results from gas production after inadequate thermal processing, post-process contamination, or survival of sporeformers that can grow in the sealed, oxygen-depleted environment of a can.

Given Data / Assumptions:

• Defect: can swelling (bulging ends, possible springer or flipper).
• Conditions inside a correctly sealed can are anaerobic.
• We must choose the primary microbial cause among listed options.

Concept / Approach:
Gas-forming anaerobic spore formers (notably Clostridium spp.) can survive insufficient retorting and, upon germination, produce gases (H2, CO2) and toxins (in some species). Because the can interior is anaerobic, obligate or facultative anaerobes dominate; strictly aerobic spore formers do not thrive in a sealed, deoxygenated can to the same extent.

Step-by-Step Solution:
Match can environment (anaerobic) to likely spoilage flora.Identify gas production as a hallmark of Clostridium growth.Select “gas-forming, anaerobic spore formers” as the primary cause.

Verification / Alternative check:
Thermal process validation targets the most heat-resistant relevant spores (e.g., Clostridium botulinum in low-acid foods) to prevent swelling and safety hazards.

Why Other Options Are Wrong:

• Aerobic spore formers: Restricted by the anaerobic can environment.
• Both: Overbroad; the primary concern is anaerobic spore formers.
• None/Only yeasts: Yeasts are generally not primary culprits in properly sealed cans, especially at low oxygen.

Common Pitfalls:
Equating any bulging with harmless spoilage; some anaerobic spore formers pose severe safety risks, requiring strict hold and destruction protocols.

Final Answer:
Gas-forming, anaerobic spore formers.