What is a common sign of milk spoilage?

A sour odor and taste are classic signs of milk spoilage. When milk spoils, bacteria break down lactose, the sugar found in milk, into lactic acid. This process not only generates a sour taste but also contributes to an unpleasant odor, making the milk undesirable for consumption. The growth of spoilage bacteria alters the freshness of milk, signaling to consumers that it is no longer safe or pleasant to consume.

In contrast, while an increase in sweetness might seem appealing, it is not a typical indicator of spoilage; rather, it can be a characteristic of specific fermented dairy products. A bright white color is usually associated with fresh milk, and any deviation may indicate other issues but does not directly signify spoilage. Lastly, a thicker consistency can result from certain bacterial activities or the presence of cream; however, this alone does not indicate spoilage as thicker milk can result from processes such as homogenization or simply being creamier due to the type of milk.