Against common belief, oats can go bad. When they do their colour will change and they will develop either an acidic or musk smell. As with everything, when in doubt just get rid of it.
Storing before using
Stored properly oats can last for up to 2 years when unopened and up to 3 months after being open. Once open, they should be kept in an airtight container in a cool and dark cupboard. Alternatively, they can be kept in the fridge to extend their life from 3 to 6 months.
Oat bran is very high in oils and will only last for up to 6 months unopened and should be refrigerated once open. Some brands of rolled oats have bran added back, these should be kept in the fridge as well.
Storing porridge and overnight oats
Once oats have been cooked into porridge refrigeration is a must. Cooked porridge should be cooled as fast as possible and put away quickly to prevent bacterial growth. The best way to do this is to either spread the porridge on a thin layer or to pack in individual servings. Overnight oats or bircher muesli should always be kept refrigerated.
Both cooked porridge and overnight oats can be warmed up using a microwave or in a pan. And they will last up to 5 days from the day they were prepared.
They can both also be frozen if they’re not going to be consumed within 5 days. To thaw, they can be left inside the fridge overnight and warmed up or quickly thawed in the microwave.
Storing other oat products
When oats are used in baking, the baked products should be treated as usual. If it’s dry (such as bannock or oat muffins) it can be left outside, if it’s moist (such as cooked oats or those popular banana oat cookies) then it’s better kept in the fridge.
Homemade oat milk or horchata will only last for 3 or 4 days (always in the fridge) but the texture will become somewhat slimy after 2 days. If the mouthfeel puts you off, you can use it for baking.