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If marinara sauce is the top dog in the world of Italian sauces and condiments, then bright and fresh pesto is certainly the runner up. This delicious mix of pine nuts, basil, olive oil, parmesan cheese, and garlic is irresistibly savory, salty, and herbaceous with a luscious texture that goes just as well slathered on a breakfast sandwich as it does spooned over a plate of pasta. With all of this potential in mind, you'll probably want to keep a jar of the sauce in your kitchen year-round. If you choose to do so, though, make sure you have a few containers for backup, as even store-bought pesto has a startlingly short shelf life after it has been opened.
Before it is opened, store-bought pesto can last quite a while. Much like other jarred foods, it's able to last on a pantry shelf for up to three months past its "best by" date. Once you remove the lid, however, the sauce starts to expire quickly. In fact, it's possible for store-bought pesto to go bad after just three days, and it is guaranteed that it won't be any good once it gets past the two week mark. Keep in mind, as well, that these estimates are only for pesto that is stored correctly — that is to say, kept in a sealed container in the fridge.
How to tell when pesto has gone bad
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Given the rate at which pesto tends to expire, it's important to keep an eye out for signs of spoilage in order to prevent yourself from consuming harmful pathogens like mold or bacteria. Use your eyes and nose to detect evidence that your pesto is no longer good. If you see a dramatic change in color, such as the sauce getting much darker, or if you smell a rancid or funky odor, then you can assume the product has spoiled. In these cases, it's best to discard the pesto and open a new jar instead of eating it.
If you find you need to stretch the shelf life of your store-bought pesto, there are several tricks you can try. One is to add a squeeze of lemon juice into the sauce, which will help to inhibit the growth of bacteria and keep the pesto good for a few extra days. Note that this will alter the flavor of the pesto slightly. Another option is to place the pesto into an airtight container and move it to the freezer, where it can last for up to eight months.
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