In this kind of business from time to time we do get calls/emails about dairy products going bad before their expiration date. Whenever we are notified of issues with milk going bad before expiration - over 95% of the time it is due to the milk getting too warm - either after delivery before it is brought in or being stored at a temperature too warm.
This occurs largely because dairy products, like ours that are low temperature pasteurized, have a low tolerance for being stored anywhere the temperature is above 36 degrees. While we do keep the milk cold in our warehouse and trucks - once we deliver our milk it is up to customers to either grab it quickly from their porch/milkbox or use ice packs; then store in a fridge that is at least below 37 degrees (preferably closer to 33-36 degrees). For reference: we keep our warehouse cooler between 32 degrees and 34 degrees at all time.
Our milk does have trace amounts of bacteria by design as with any other milk that is not Ultra Pasteurized and the reason milk goes sour is because the bacteria is always replicating and keeping the milk stored at a cold temperature tremendously slows down this process.
Here is a chart that shows how temperature effects the shelf life of your dairy products:
Source: National Milk Producers Federation
Here is an additional source confirming the same results:
Source: https://www.chegg.com/homework-help/constructing-line-graph-diagram-milk-carton-figure-7-shows-r-chapter-r.8-problem-61p-solution-9780534432959-exc
It's quite common to believe your refrigerator is cold enough (below 40F) because it feels cold. We have experienced refrigerators that feel cold even though they are 50 degrees - this is cold compared to the indoor temperature average of 65F+ in the home. Very often when we have an issue and ask customers to check their temps in their fridge they are in the high 30s or even mid 40s. This will dramatically shorten the shelf life of dairy products along with any other perishable products. Usually temperature settings on the refrigerator can be dialed back enough to get the ideal temperatures between 33-36 degrees; which would nearly double the shelf life of stored milk.
In addition, it is important to store your milk in the coldest part of the refrigerator. Storing milk in the door can often lead to it being 3 or 4 degrees warmer then on the shelves and if your refrigerator is not in a climate controlled environment (such as a garage) there can be large fluctuations in temperature between the day and night and the changing seasons.
All this is not to say we won't refund you for your bad milk , but this is an important consideration when solving issues of our dairy products turning prior to their expiration - since the issues are likely to keep happening in the future if the storage temperature is not corrected.
Thanks,
Andrew - Co-Owner Wasatch Milk