How To Tell If Butter Is Bad?
It can be challenging to know when a tub of butter has gone wrong, but luckily, there are simple ways to determine when the spread is spoiled. If the butter has turned rancid, it has two main signs: a discolored and moldy appearance and a foul taste. It’s also best to discard the butter if you see it. If you don’t recognize these signs, you can always ask your butcher to check them for you.
Another noticeable sign of rancid butter is a powerful smell. Usually, butter has a faint, sour odor.