What is a good way to check if cooking oil in an unopened bottle stored for a while might have gone rancid?

Answer 1

Ew. If you have to ask...

Seriously, your bottle should have a "best used by" date printed on the label. Olive oil should be stored in a cool, dry place, (i.e. room temperature in a dark pantry is ok.) It can last up to 15 months, under ideal conditions.

Corn oil is different. According to The Food Channel, it should be stored in the refrigerator, for up to 6 months.

Now, in order to test whether your oil has gone bad:

1. smell it. If it smells rancid or mouldy or weird, then chuck it in the bin.

2. no smell? taste it. If it tastes bitter or gross, then chuck it in the bin.

Your question just said, "cooking oil" and did not refer to a specific oil. Best to check the label, or ask your grocer when you buy it. Different oils last different amounts of time before they go bad.