How Long Pesto Is Good For Once It's Opened
You can always recognize pesto in a dish when you see it: if your pasta or pizza is a bold green — and it's supposed to be green — it's made with pesto. But if you're cooking with pesto, how long will it last before it spoils?
Store-bought pesto comes in different varieties: refrigerated and unrefrigerated, which are often sold in different aisles of the grocery store. Refrigerated pesto has a shorter best-eaten-by date, and can last up to a week in the fridge once it's open, though sometimes it only lasts a few days. Unrefrigerated pesto lasts longer, and can survive for one to two weeks after you open it — however, it should go into the fridge once you pop open the container.
However, it does depend on the brand: Rao's recommends using their pesto sauce before 10 to 12 days, while Barilla recommends using theirs within five days — both of these are canned and unrefrigerated. Buitoni recommends using their refrigerated sauce within just three days. So always check the container to see if the pesto you're holding has specific guidelines.
Pesto, presto
With store-bought sauce, the refrigerated version of pesto has fewer preservatives, which is why it needs to stay cold even before it's opened. Unrefrigerated pesto usually comes in canned or powdered varieties and contains more preservatives because it's designed to sit in your pantry until you need it. Powdered pesto mix usually lasts a few weeks longer than the canned variety before opening, but they both even out to that one-to-two weeks once they're unsealed. In any case, you'll likely use most of the pesto for a single dish, so don't feel like you need to save it.
However, if you've made the pesto yourself, then the National Center for Home Food Preservation recommends storing it for no longer than three days in the fridge. It will start to go stale after this point, though a sealed container of homemade pesto can last up to five days. It can be frozen for much longer, however. Frozen pesto of any variety should last up to three months in the freezer, although its texture might become more grainy and its color may be darker after it's thawed.
Shades of green
Pesto gets its color and freshness mainly from basil, which is its main ingredient; you make pesto by mixing basil leaves, pine (or even pistachio) nuts, garlic cloves, parmesan, and olive oil, and then you grind or blitz them up into a green paste. The leaves and nuts contain oils that can go rancid quickly, which is why pesto doesn't last especially long without preservatives.
So how can you tell if your pesto has gone bad? If there's any mold growing then you should toss it all immediately. Don't just remove the moldy parts, because once you can see mold, there's always more underneath that you can't see. If your pesto has turned brown instead of green, that's another clear sign that it's rancid. And there's always the smell test: it will have a strong sour smell once it turns. But as always, it's better to err on the side of caution and throw the pesto out if you've got any doubts.