Why Swiss Cheese Has Large Holes (Propionibacterium)
Biology · Microbes in Human Welfare · NEET
Swiss cheese has large holes because the bacterium Propionibacterium sharmanii makes a lot of carbon dioxide (CO2) gas while the cheese ripens. This trapped gas forms the big round holes, also called "eyes". Memory hook: "Propioni Pops holes with CO2 Puffs" in Swiss cheese.
Propionibacterium sharmanii makes a large amount of CO2 during ripening; the trapped gas forms the large round holes (eyes) of Swiss cheese. Remember: CO2 only, not H2.
Your doubts, answered
Which microbe makes the large holes in Swiss cheese?
The bacterium Propionibacterium sharmanii. NCERT names this exact species, so learn the full name for NEET, not just "a bacterium".
What actually forms the holes?
A large amount of carbon dioxide (CO2) gas made by Propionibacterium during ripening. The gas gets trapped inside the solid cheese and forms big round holes (eyes).
Is it CO2 only, or CO2 and H2?
CO2 only. NCERT says the holes are due to a large amount of CO2. NEET options that add H2 (hydrogen) or a different microbe are traps. Only CO2 by Propionibacterium is correct.
Does Lactobacillus make the holes?
No. Lactobacillus (lactic acid bacteria) makes curd and helps give cheese its texture and flavour, but the large holes are specifically from CO2 produced by Propionibacterium sharmanii.
Is Propionibacterium used in household products?
Yes, because Swiss cheese is a household food product. NEET 2025 tested this exact point: Propionibacterium sharmanii is counted as a household-product microbe.
⚠️ The NEET trap ✗ Swiss cheese holes are made by CO2 and H2 gas produced by Lactobacillus. ✓ Swiss cheese holes are made by a large amount of CO2 (only) produced by Propionibacterium sharmanii. 🧠 NTA loves swapping the microbe and adding a fake second gas. Lock in: Propionibacterium + CO2 only. No H2, no Lactobacillus.
Real NEET questions
NEET 2026
What is the reason behind production of large holes in 'Swiss Cheese'?
A · The production of large amount of CO2 by Propionibacterium sharmanii ✓
B · The production of large amount of CO2 by Clostridium butylicum
C · The production of large amount of CO2 and H2 by lactic acid bacteria called Lactobacillus
D · The production of large amount of CO2 and H2 by Trichoderma polysporum
Solution: The large holes (eyes) of Swiss cheese are caused by a large amount of CO2 produced by Propionibacterium sharmanii during ripening. Note the traps: option C wrongly uses Lactobacillus and adds H2, and options B and D use the wrong microbes. Only CO2 by Propionibacterium is correct.
NEET 2025
Which of the following microbes is NOT involved in the preparation of household products? A. Aspergillus niger B. Lactobacillus C. Trichoderma polysporum D. Saccharomyces cerevisiae E. Propionibacterium sharmanii
A · C and D only
B · C and E only
C · A and B only
D · A and C only ✓
Solution: Lactobacillus (curd), Saccharomyces cerevisiae (bread/dough) and Propionibacterium sharmanii (Swiss cheese) ARE household-product microbes. Aspergillus niger (industrial citric acid) and Trichoderma polysporum (cyclosporin/biocontrol) are NOT household microbes, so the answer is A and C only. This confirms Propionibacterium belongs to the household group.
Solved Microbes in Human Welfare NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is the full scientific name to write in NEET?
Propionibacterium sharmanii. Write the full binomial name because NEET options often list several bacteria and only the correct species scores.
Why does the gas form round holes and not escape?
During ripening the cheese is firm and solid, so the CO2 gas cannot escape easily. It gets trapped in pockets and pushes the cheese outward into round holes called eyes.
Does Propionibacterium also affect taste?
For NEET, its key role is making CO2 that forms the holes. Overall cheese flavour and texture also depend on other microbes and ripening, but the holes point is the exam-tested fact.
Is this a high-yield NEET point?
Yes. It was asked directly in NEET 2026 and indirectly in NEET 2025. The microbe-to-product matching in Microbes in Human Welfare is repeatedly tested.
