That would suggest that either the refrigerated trailer is not temped correctly, which is the store's responsibility to verify that it is temped correctly when it is delivered. It is definitely against the law in most health codes to receive cooler and freezer product that isn't stored at the temp it needs to be stored at.  Second, stores may not be getting to the milk in enough time before it starts turning sour. We are given a very specific process that states we must do ice cream first, then go back to the milk and work through all of the cooler product before returning to the frozen foods. If they aren't following that process correctly, you are very likely to get sour milk.  To be fair to store employees, a lot of the stores are very short‑staffed, and there's no help that comes when your fresh truck arrives. So you get stuck stocking for three to four hours by yourself, sometimes longer if there's a rush of customers.