Is rancid butter OK to use in baking?

Butter often goes rancid because it hasn't been stored correctly – warm temperatures, light and moisture can all cause butter to deteriorate quickly and become rancid.

There are two main signs that butter has started to become rancid:

1. There is a darker yellow layer around the outside when you cut into a block of butter
2. You also notice the butter has a slightly sour smell 

If the darker yellow layer is quite thin and the aroma isn't too sour, then you can just cut away the outside layer before using. However, if the darker yellow goes deep into the butter and the smell is unpleasant it is best not to use the butter as it will taint the final flavour of your bake.

To prevent butter going rancid in the future, always buy butter that has a foil-like wrapping (light can easily penetrate thin, paper-like wrapping and the oxidation process that causes the butter to go rancid may well have started while being stored in the shop). Keep the butter in its original wrapping in the main part of the fridge – the butter compartment is not cold enough to keep blocks of butter in it for any length of time. Any leftover butter should be rewrapped and placed in an airtight container or sealed plastic bag and used soon after to avoid it absorbing other flavours from the fridge – you certainly don’t want your chocolate brownies tasting of fish.

Butter will keep for up to eight weeks in the fridge if stored correctly but I would recommend buying it as you need it. Also remember to check the used by date for optimum freshness. Unopened butter can be frozen in a sealed freezer bag for up to six months and thaw it in the fridge before using.