Double cream thickening and becoming less pourable after being in the fridge for a day or two is a natural process known as creaming. Creaming is caused by the separation of fat from the liquid in the cream. Double cream typically has a higher fat content than regular whipping cream, making it more prone to creaming.
Here's what happens during creaming:
Fat Separation: In double cream, fat molecules are dispersed throughout the liquid. Over time, these fat molecules start to cluster together and rise to the top of the cream due to their lower density compared to the liquid portion.
Coalescence: As the fat molecules rise, they begin to coalesce and form larger fat globules. These fat globules combine to create a thicker layer of fat on the surface of the cream.
Liquid Remaining: The liquid portion of the cream, which contains some water and milk solids, remains below the fat layer. This separation of fat and liquid is what causes the thickening of the cream.
The process of creaming is a natural occurrence and doesn't necessarily mean that the cream has gone bad or spoiled. You can still use the thickened double cream, but you'll need to stir or gently whisk it to redistribute the fat back into the liquid, returning it to a smoother consistency.
If you find the cream has an off odor, unusual texture, or other signs of spoilage, then it's best to discard it. Otherwise, just stir it well before use, and it should be fine for cooking or whipping. If you want to avoid creaming altogether, try using the cream within a day of purchase or follow proper storage techniques, like keeping it in an airtight container to minimize exposure to air.