Milk expires because of the buildup of bacteria, yeast, or mold that break down the milk over time, causing it to spoil.
What Causes Milk to Spoil?
The primary reason milk goes bad is microbial activity. Here's a breakdown:
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Microbial Growth: Milk provides a nutrient-rich environment for various microorganisms. Bacteria, yeast, and mold naturally present in milk (even after pasteurization) will multiply over time.
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Breakdown of Milk Components: As these microorganisms grow, they consume lactose (milk sugar), proteins, and fats in the milk. This process leads to the production of undesirable byproducts such as lactic acid and other compounds.
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Sensory Changes: These byproducts alter the milk's taste, smell, and texture, resulting in the characteristic signs of spoilage.
- Sour Smell: The production of lactic acid gives spoiled milk its sour odor.
- Clumpy Texture: Protein breakdown can cause the milk to curdle and become lumpy.
- Off-Flavor: Various compounds produced by microbial activity create unpleasant tastes.
How to Identify Spoiled Milk
According to the reference information, it is very easy to identify rotten milk using sensory clues. The best way to tell if milk has expired is to trust your senses. As O'Brien says, "If it doesn't look right or smell right, it's probably spoiled." Here's a way to test that:
- Visual Inspection: Check for changes in color or the presence of lumps.
- Smell Test: Sniff the milk for a sour or off-putting odor.
- Taste Test: If the milk looks and smells okay, taste a small amount. A sour or unpleasant taste indicates spoilage.
