What might a bulk milk hauler detect in raw milk if it has a sour odor?

A sour odor in raw milk is often a clear indication of changes in its quality, primarily associated with a high titratable acidity. This happens because the sourness typically results from the activity of bacteria that ferment lactose into lactic acid, raising the acidity of the milk. When the titratable acidity increases, it directly correlates with the development of sour flavors and odors, signaling that the milk may not be suitable for consumption or further processing.

Other aspects of milk quality, such as low fat content, excessive cream, or a high bacterial count, may not necessarily produce a sour smell. While a high bacterial count can be related to the sourness (as some bacteria produce lactic acid), it is the increase in titratable acidity that is most directly linked to the odor. Thus, identifying the high titratable acidity would indicate that the milk degradation process has begun, confirming the sour smell.