Butter has a relatively long shelf life, but it’s still a perishable dairy product that can spoil. Factors that can affect the shelf life of butter include how it's stored and whether it's salted or unsalted, so here is how to tell if your butter has gone bad.

Assessing the color of your butter is important for knowing if it’s spoiled or not, as fresh butter is usually light yellow but can turn darker or even beige if it’s bad. Venae Watts, a butter maker at Minerva Dairy, says that spoiled butter will also show mold or other colored spots, and she recommends taking a small taste to see if it’s truly spoiled.

If you don’t want to taste it, you can smell your butter to see if it has gone bad, as rancid butter will have a sour or stale smell that is quite noticeable. Additionally, if your butter has a greasy or slimy texture, it has likely gone bad, because fresh butter should be smooth and firm.

Generally, salted butter has a longer shelf life than unsalted butter because salt acts as a preservative, but you can keep your butter fresher for longer by making sure it’s sealed tight in the coldest part of the fridge. Unopened butter can last in the fridge for up to three months, and opened butter can stay good for two weeks.