Whether you're buying ice cream from the grocery store or making it from scratch, there's a way to keep it at its creamy best and plenty of ways to go wrong. Here's what you should think about: where you're storing it, how you're storing it, and the last time you took your freezer's temperature.
If there's one thing to know about storing ice cream, it's this: it hates changes in temperature. In an ideal world, freshly churned ice cream should be chilled down to as low a temperature as possible, slowly defrosted until it's scoopable, and then eaten all in one sitting. Every time ice cream increases in temperature, some of the ice crystals trapped inside melt. This is fine if you plan to eat your ice cream right away, but when you re-freeze partially-melted ice cream, those ice crystals re-form—but this time they're bigger and crunchier, robbing your ice cream of its creaminess.
So your goal as a responsible ice cream eater and maker is to keep your ice cream as cold—and stable—as possible.
Store your ice cream in the very back of the freezer, as far away from the door as possible. Every time you open your freezer door you let in warm air. Keeping ice cream way in the back and storing it beneath other frozen-sold items will help protect it from those steamy incursions.
By this same token, don't leave your ice cream out of the freezer any longer than you have to. If your homemade ice cream is half-melted, you're better off letting it melt all the way and churning it again.
Ice cream is best stored below 0°F. If you have a freezer thermometer, adjust your freezer's settings to maintain this temperature. If you don't, go out and buy one. Or take the easy way out: set your freezer dial for as cold as possible. Your ice cubes can take it.
Don't underestimate the importance of a cold freezer for firming up your freshly churned ice cream. Without it your ice cream will turn icy and crunchy, ruining all your hard work.
Size (err...Shape) Matters
If you're making ice cream at home, your storage vessel makes a difference. Pro ice cream makers have the benefit of blast chillers to deep-freeze ice cream in minutes. Doing so keeps ice crystals small, leaving the ice cream just as fresh and creamy as when it was churned. You can get a blast chiller at home for a mere five grand.
Or you can use a storage container that encourages speedy freezing of ice cream. What you want to look for is a shape with a high surface-area-to-volume ratio that'll expose the mass of the ice cream to cold air—something wide and flat rather than compact and boxy. Counterintuitively, ice cream pints are not the best shape for storing homemade ice cream.
My favorite ice cream container is a five-cup model from Rubbermaid. It's durable, cheap, stackable, reasonably airtight, and most importantly—flat. Ice cream freezes fast inside with minimal ice crystals. And it's just the right size for a quart of homemade ice cream with head room for mix-ins.
You can also freeze your ice cream in several smaller containers, which will freeze faster than a single larger one. But it's harder to scoop from smaller containers; the larger one above gives you plenty of room to work with.
No matter what shape or size your container, stick to plastic over ceramics or glass. Both are poor conductors of heat, and even in a properly chilled freezer, ice creams stored in glass take too long to freeze.
Keep it Airtight
Ice cream is full of fat, and even when frozen, fat has a way of soaking up flavors from the air around it—including those in your freezer. To keep your ice cream from taking on the odor of that fish or last week's chili, use a container with a tight-fitting lid. For extra security, place a layer of plastic wrap between your ice cream and the lid.
Air is also responsible for freezer burn, which desiccates and crystalizes the surface of ice cream. A tight lid helps, but air trapped inside the container over long periods will also do damage. As you eat more of your ice cream, consider transferring it to a smaller container. Smaller containers mean less ambient air, which means less risk of freezer burn.
But regardless of how airtight your ice cream container is, prolonged time in the freezer will degrade homemade ice cream's flavor and texture. For best results, ice cream should last for no more than a week or two. With good ice cream that shouldn't be a problem.