What is the cause of large holes in swiss cheese?

Explanation

**Step-by-Step Solution:**

1. **Identify the Microorganism:** The primary cause of large holes in Swiss cheese is a bacterium known as *Propionibacterium shermani*.

2. **Understand the Fermentation Process:** This bacterium plays a crucial role in the fermentation of cheese. It converts lactose (the sugar found in milk) into lactic acid.

3. **Conversion of Lactic Acid:** The *Propionibacterium shermani* then further converts lactic acid into propionic acid and carbon dioxide (CO₂).

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