We are all familiar with the saying “don’t cry over spilt milk,” but what about spoiled milk? Discovering that your milk has gone bad in the fridge can be quite frustrating. Many people use milk daily without fully understanding what causes it to spoil.

The key factor behind milk turning sour is the rapid multiplication of bacteria within the milk. This process converts lactose (milk sugar) into lactic acid, resulting in a sour taste and the formation of clumped proteins, leading to a thick, lumpy texture.

While you cannot prevent milk from eventually spoiling, there are ways to slow down this process. Avoid introducing new bacteria into the milk, such as by drinking directly from the bottle, and ensure your milk is kept consistently chilled, as bacteria multiply more rapidly above 4°C.

The shelf life of milk depends on the type of milk and how it is stored. Pasteurised milk, the most common type in the UK, undergoes heating and rapid cooling processes that eliminate harmful bacteria, extending its shelf life to up to 10 days unopened and three to seven days once opened.

Plant-based milk alternatives, like oat milk, have varying shelf lives. Refrigerated oat milk lasts around 7-14 days unopened and five to seven days once opened, while UHT oat milk can last months unopened but should be consumed within 7-10 days once opened.

Filtered milk undergoes additional filtration to reduce microbes, resulting in a longer shelf life of seven days after opening and 21 days unopened, compared to standard pasteurised milk.

UHT milk, heated to high temperatures for a short period, has the longest shelf life among milk types, lasting six to nine months unopened when properly packaged but only seven to 10 days once opened.

Proper temperature control is crucial for maintaining milk freshness. Store milk in a fridge at around 2-3°C, avoiding the door’s warmer areas. Filtered milk, like Arla Cravendale, lasts longer due to its purification process and protective packaging.

To determine if milk is still fresh, conduct a simple check: smell it for neutrality, examine for lumps, try the hot water test for curdling, and taste a small amount. If it passes these tests, it is likely still consumable, regardless of the label date.

Understanding these factors and taking the necessary precautions can help prolong the freshness of your milk and reduce waste.