This condition is fairly common and can happen at times even when the same successful routines have been followed. There are spoilage bacteria in milk and colostrum that release acid as their by-products. This is usually lactic acid but there are also others. The release of acid from these proliferating bacteria then drives down the pH of the milk making it more acidic. Once the product is pasteurized it is safe for the calves to drink, but this can lead to rancid odors and flavors that might decrease consumption by the calves. Digestibility might also be different which can lead to scours. In cases of severe drop in pH, the milk will separate completely with a very thick layer of “cheese” on top or thick like pudding throughout the product. This is not due to overheating, it is due to the fact that protein denaturation and separation is made worse by the added heat of the pasteurization process. Heat combined with spoiled milk of low pH is a bad recipe which is why we recommend that you always try to pasteurize as soon as possible after harvest.