Marshmallows have two seasons: Rice Krispies treat season, which is around the holidays, and s’mores season, which is now. Unless you’re a true ‘mallow head, you probably don’t go through that many bags of the fluffy white confection each year. In fact, you could have a half-consumed bag of marshmallows hanging out in your pantry right now, getting all stale and sticky.
How to keep marshmallows from going stale
Prevention is the best medicine. A bag of marshmallows, unopened, will stay fresh for up to a year, but once opened, they start battling the air (and losing).
Marshmallows are essentially little sponges, with air trapped in a network of sugar. They are prone to absorbing moisture, and that moisture wrecks the delicate network of sucrose, causing the candy to deflate and get sticky. Keeping them in an airtight container will help, but adding a piece of plain white sandwich bread, which will absorb moisture from the air in the container, can extend the freshness window even further.
You can also freeze them. According to Can You Freeze This?, frozen marshmallows come out of the icebox a little hard, but will fluff back up when they thaw. (Water is the main culprit when it comes to freezer-related texture issues, and marshmallows are pretty devoid of water.) Just transfer your marshmallows from the (open, half-used) bag to a freezer bag, remove as much air as you can, and chuck them in the freezer, where they will keep for up to four months. Most commercially-produced marshmallows come with a fine coating of cornstarch, so they won’t stick together in a big block, but it may be a good idea to coat any fancy, artisanal marshmallows with a little cornstarch or powdered sugar before freezing.
How to revive stale marshmallows
If you dig a bag of marshmallows out of your pantry to find them super sticky and discolored, go ahead and toss them. But if they’re only little bit sticky and deflated, you can transfer them from their original packaging to an airtight container with a piece of sandwich bread and see if that perks them up in a couple of days.