Off-flavors in milk such as acid, high acid, or sour milk are usually caused by what?

Off-flavors in milk, particularly those described as acid, high acid, or sour milk, are predominantly caused by microorganisms. When milk becomes contaminated with certain bacteria, it can lead to the fermentation of lactose, which produces lactic acid. This process is what creates the sour taste associated with spoiled milk, and the presence of this acid can significantly alter the flavor profile of the product.

Microorganisms such as Lactococcus lactis or various yeasts and molds are often responsible for this type of off-flavor. Inadequate refrigeration, poor sanitation practices, and extended storage times can exacerbate the growth of these bacteria, leading to a decrease in milk quality.

In contrast, environmental factors could influence the overall environment and handling of the milk but are not the primary cause of sourness or acid flavors. Packaging material, while it might interact with the milk, generally does not create these off-flavors. Similarly, milk processing methods can affect the flavor, but if proper sanitary practices and temperature controls are maintained, they should not cause sour or high acid flavors directly related to microbial activity.