Why does milk go bad?

 How come milk does not go bad inside of a cow, and it is not even cold inside the cow. Yet it only takes a couple of days for milk left out of the fridge to go bad?

Milk goes bad because of the presence of bacteria. Raw milk naturally contains bacteria, and even pasteurized milk can be contaminated with bacteria during the milking process or after it has been pasteurized. Bacteria will grow and multiply quickly in milk if it is not stored properly.

Milk spoilage occurs when bacteria breaks down the lactose (milk sugar) and produces lactic acid, which causes the milk to become sour. As time goes on, the bacteria produce more lactic acid, which lowers the pH of the milk and causes it to curdle or form clumps.

The factors that affect how quickly milk goes bad include temperature, exposure to light, and the type and number of bacteria present. Milk should be stored at or below 40 degrees Fahrenheit to slow the growth of bacteria. If the milk is left out at room temperature, the bacteria will multiply rapidly and the milk will spoil very quickly.

Other factors that can cause milk to spoil include exposure to light and improper handling. Exposure to light can cause a breakdown of vitamins and other nutrients in the milk, which can lead to rancidity and off-flavors. Improper handling, such as using dirty utensils or not washing hands before handling milk, can introduce bacteria that will cause the milk to spoil.

In conclusion, milk spoils due to the presence of bacteria that break down lactose and produce lactic acid, which causes the milk to become sour and eventually curdle. Factors such as temperature, exposure to light, and improper handling will affect how quickly milk goes bad. Proper storage, handling, and hygiene practices are important to prevent milk spoilage.