How to Prevent Stale Marshmallows
Marshmallows have two seasons: rice crispy treat season, which falls around the holidays, and s’more season, which is now. Unless you’re a true mallow fanatic, you probably don’t eat as many bags of fluffy white confection each year. In fact, you might have a half-eaten bag of marshmallows hanging in your pantry right now, getting stale and sticky.
How to make marshmallows not stale
Prevention is the best medicine. An unopened bag of marshmallows stays fresh for up to a year, but once opened, it begins to struggle with air (and lose).
Marshmallows are essentially little sponges with air trapped in a mesh of sugar. They tend to absorb moisture, and this moisture breaks down the fine network of sucrose, causing the candies to deflate and become sticky. Storing them in an airtight container will help, but adding a piece of plain white sandwich bread that 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 are difficult to get out of the refrigerator, but when thawed, they will fluff up again. (Water is the main culprit in freezer-related texture problems, and marshmallows are virtually water-free.) Simply transfer marshmallows from an (open, half-used) bag to a freezer bag, removing as much air as you need. you can, and throw them in the freezer, where they will keep for up to four months. Most commercial marshmallows are coated with a thin layer of cornstarch so they won’t stick together into a big block, but it can be a good idea to coat any fancy, artisanal marshmallow with a little cornstarch or powdered sugar before freezing.
How to revive a stale marshmallow
If you pulled a bag of marshmallows out of the pantry and found them very sticky and discolored, throw them away. But if they’re only slightly sticky and deflated, you can transfer them from their original packaging to an airtight container with a slice of sandwich bread and see if they perk up after a couple of days.