by Michael Hawkins
Short answer
Once opened, a jar of pesto lasts in the fridge for three days without any dramatic loss of quality. It will be perfectly safe for another two days, but leave it any longer, and its quality will decline to the point that it will no longer be enjoyable to eat.
Long answer
How long pesto lasts in the fridge is dependent on several factors, but providing you follow all the following conditions, an opened jar of pesto will remain perfectly safe for up to five days.
1.) Your fridge is set to the recommended temperature of 5°C or below.
2.) The sauce is not already past its expiration date.
3.) The jar hasn't been left standing at room temperature for more than two hours.
4.) It has a thin layer of oil over the top to prevent air from turning the sauce brown.
If you can't remember how long a jar of pesto has been sitting in your fridge, don't rely on a sniff test. You cannot detect botulism by sight or smell, so it's simply not worth the risk.
Similarly, if you can see mould starting to form on the surface of your sauce, don't be tempted to scrape it off and eat the rest. Mould could have already permeated all parts of the sauce, and the whole lot should be thrown away without a second thought.
Safety is only one part of the equation, though. Even though keeping pesto in a fridge makes it last longer, all sauces begin to deteriorate as soon as you twist the lid. So, even if you don't need to worry about food poisoning, you should be aware that your five-day old pesto won't taste nearly as good as a freshly opened jar.
Pouring a thin layer of oil on top to restrict the sauce's exposure to oxygen will help keep your pesto looking (and tasting) better for longer and is the most effective way to ensure your pesto doesn't turn brown or become bitter.
If you don't plan to eat more pesto in the next five days, don't forget that it freezes remarkably well. We like to freeze pesto in an ice cube tray so that we always have some tasty nuggets at our disposal whenever we think a dollop of pesto could improve our dinner.
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