Because a stale croissant is a sad croissant
There's nothing sadder than taking a bite of croissant, expecting it to be flaky, and finding out it's gone stale. That's why baker Zachary Goper jokes that, "The absolute best way to store a fresh croissant is to keep it in your tummy after you've just enjoyed it." The owner of Brooklyn bakery Bien Cuit and James Beard Award semi-finalist for outstanding baker explained in an email to Extra Crispy that croissants have an upsettingly short shelf-life once they've been taken out of the oven. When I asked Goper to elaborate on exactly how long croissants can stay fresh, he turned the question back on me: "Like, really nice? Six to ten hours. Pretty nice? Maybe 16 to 24 hours."
Not everyone has access to freshly baked, perfectly flaky croissants, pulled straight from the oven every morning. And though that's still the best way to get your hands on a fresh croissant, it's actually pretty easy to keep croissants fresh overnight. "If you bought too many or are planning for the next morning's breakfast, you can leave them in a paper bag rolled shut for up to 36 hours before the texture really starts to suffer," Goper says. "Any point within those 36 hours, they can be refreshed in a 365°F oven for three minutes, then allowed to cool completely before enjoying them."
If you're not going to eat your fresh croissants within 36 hours, the best way to keep them fresh is to freeze them in some kind of airtight container. The best way to freeze croissant is the same method you'd use to freeze bagels or breads or any other pastries. You can start by with wrapping croissants in plastic wrap and then popping them in a resealable plastic bag with all the air taken out. "But you should do that as soon after they were baked as possible," Goper says, otherwise you're just freezing already-stale croissants, which kind of defeats the point of saving the croissants in the first place.
To defrost croissants without destroying them, first let the croissants thaw completely, then take them out of the airtight container. Once they're thawed out, you can revive them just as you would slightly stale croissants. Simply "place them in an oven preheated for 365°F for about three to four minutes," Goper says, "and let them come to room temperature before eating." It's as close to fresh out of the bakery oven you're going to get without a bakery oven.