The trouble started when I made a bowl of oatmeal the other day. Two bites in, I realized something didn’t taste right. The oatmeal tasted salty, a little sour, and just off. I sniffed the milk—it was fresh. I tasted the almond butter I’d dolloped on the oatmeal. That too was just fine. There was no question—my oatmeal was rancid. How? Why? I thought oats rarely, if ever, go bad!
I took to the internet, as I am wont to do in such moments. Most food safety resources confirmed that oats rarely go bad before you’ve finished the container. They will stay fresh if kept in an airtight container in a cool, dry place for at least 12 months once the container has been opened.
Full disclosure: On that particular day, I was out of the old-fashioned rolled oats I always use. Instead made my porridge with fancier, rolled oats I had in the back of my fridge. I’ll be honest, they were definitely about 12 months old. But I’d used them in cookies the week before and noticed nothing wrong, so I assumed they were fine. Not so much. Here’s what I found out in my research.
2 Reasons Oats Go Bad
Though oats have a relatively long lifespan, here are two reasons why some oats may go bad before you get to enjoy them:
1. Unprocessed Oats Spoil Faster
Oats can go bad more quickly if they haven’t been commercially processed. Standard rolled oats you’ll find at the store—like Quaker Oats—begin as oat groats that are first dehusked and rolled into flakes, then are treated with wet steam and toasted lightly in order to stabilize the grains. After the oats go through this processing, the oats will stay fresh for longer.
The oats I used the other day were unsteamed (also known as unstabilized), and therefore contained unstabilized oils, which was a likely culprit for why they went rancid.
2. The Packaging Makes a Difference
Another reason oats can go bad has to do with packaging. If the oats are packaged in paper, airborne yeast and humidity can enter the bag and spoil the product. Unlike mold, which is a very obvious indicator of spoilage—mold can grow on oats if they’re exposed to moisture—these yeasts are pretty much invisible. While affected oats will still look OK, their sour flavor will convince you otherwise. That is why oats stored in a non-porous airtight container will last longer.
How To Store Oats
Preventing oats from going bad is easy. If the oats are stored in paper, after opening the package, transfer the grains to an airtight glass or metal container and stash them in the fridge or freezer. This is also a great way to prevent other nuisances that can arise in a pantry situation, like mealy bugs (sorry for the nightmares).
If the oats are processed, they’ll probably be fine in the fridge for one year; if they’re unsteamed, it’s best to finish them off within four to six months.
A version of this article originally appeared on MyRecipes.com.