As a food science expert with a focus on dairy products, I can tell you that milk can spoil due to several reasons. The primary cause of spoilage is the growth of microorganisms, such as bacteria, which can multiply rapidly when the milk is not properly refrigerated or pasteurized. When these microorganisms reach high levels, they can produce off-flavors, change the texture, and even become harmful to health.

Another factor that can lead to spoilage is improper handling or storage. Milk should be kept at a consistent cold temperature, ideally below 40°F (4°C), to slow down the growth of bacteria. If milk is left out at room temperature for too long, it can spoil quickly. Additionally, if milk is exposed to light, especially sunlight, it can cause a breakdown in the milk's proteins and fats, leading to spoilage.

Contamination from other foods or dirty containers can also introduce spoilage-causing bacteria into the milk. It's important to always store milk in a clean, airtight container and to avoid transferring bacteria from hands or other surfaces.

Finally, the natural enzymes present in milk can also contribute to spoilage over time. These enzymes can break down the milk's proteins and fats, causing it to sour or curdle.

read more >>

Bacteria tend to get a lot of bad press. But lactic acid bacteria occur naturally on plants like grasses and can easily end up in milk. They ferment lactose at room temperature and turn it into lactic acid. More acid means more hydrogen ions, a lower pH and a sour taste.read more >>