Many of us tend to think of freezers as versatile little time machines. Don't want to complete that recipe 'til later? Throw it in the freezer. Don't want to finish that ice cream? Keep it in the freezer. Don't want to deal with Han Solo right now? Freeze him in carbonite.
But while the uses of a household freezer are numerous, they won't solve all your problems. There are plenty of foods and drinks that won't hold up in a freezer, and a few that actually become dangerous when frozen. You can either figure these out the hard way, or simply read on....
Worse When Frozen
Foods in this section won't turn after freezing, and they probably won't ruin any recipes, but you're better off keeping them unfrozen to avoid certain adverse effects.
Pasta will do fine in the freezer as long as it hasn't been cooked yet. But after boiling—and thus imparting lots of water into your macaroni—it's no longer ideal to freeze. Pasta like this ends up mealy when thawed and, more importantly, my Italian grandmother never freezes pasta. So there.
Egg Whites & Meringue
While freezing whole eggs presents its own problems (more on that later), freezing only the whites isn't a good idea either. The high-protein, watery whites become rubbery and spongey after freezing. Foods made from egg whites (meringue is basically just whipped egg whites) will fall victim to the same effect.
Freezing anything fried will cause the delicious breaded exterior to saturate and become mushy. It's still edible, but you'll be robbing yourself of the full crunchy satisfaction of a hot mozzarella stick, or a jalapeno popper, or a frickle (that's a fried pickle), or a fried Oreo cookie, or a fried Twinkie.
I should go on a diet.
Leafy Green Produce
Here we're talking about cabbage, celery, lettuce, and the like. Cucumbers too. These items will become limp, and lose both their color and aroma. Once thawed, leafy produce may still be okay for cooking with, but forget making a nice crisp salad.
Green Onions & Tomatoes
Again, green onions and tomatoes will be adequate as part of a recipe after freezing, but they'll lose their texture along the way. If you plan on eating either of them raw, forget freezing.
Cut it out! You're not even supposed to refrigerate potatoes, much less freeze them! Simply dry off your potatoes and leave them in a cool, dark place. They'll keep for months, and taste better too!
Almost All Fruits & Berries
Fruits (especially those with high water content, like watermelon) and berries should not be frozen unless you plan to eat them frozen. During the thawing process they'll lose their rigidity, texture, color, and taste. In other words, they'll become gross. On the other hand, frozen strawberries are a superior smoothie ingredient, and frozen blueberries are perfect over ice cream.
I should really go on that diet.
Wine (Except Champagne)
Champagne gets its own section later on, but for most other wines, freezing is only less than ideal. Don't freeze expensive wines, because much of the flavor will be lost, but cooking wines destined for sauces and reductions can be safely frozen.
Ruined When Frozen
These frozen or thawed foods are still safe to eat, but rendered pointless or detrimental to a recipe during the freezing process.
Gelatin will "weep" as it thaws, meaning some or all of it will return to liquid form. For certain recipes this won't matter, but if you're making Jell-O it's pretty much a deal-breaker. Gelatin really shouldn't even be refrigerated for long periods at a time, but a teaspoon of cornstarch will stave off weeping in the fridge. Frozen gelatin can't be saved by cornstarch though, and your only hope is to eat it frozen.
Sour Cream, Mayonnaise, & Salad Dressing
These ingredients will separate when frozen, and that's bad news in situations when the water can't be recombined. Sure you can stir together a tub of separated sour cream, but you're in trouble if that sour cream is already in a cake frosting mix, or on top of a taco. Same for mayo on a BLT, or salad dressing on... a salad, I guess.
Herbs & Spices
Herbs "last longer" in the freezer but at the cost of their potency, making the process a waste. Some spices—particularly black pepper, green pepper, imitation vanilla, cloves, and garlic—even become bitter when frozen. Frozen paprika doesn't become bitter, but takes on a different, inferior taste.
Dangerous When Frozen
Freezing any of these items would be an embarrassing way to get yourself sick, or even injured. Don't do it.
Unlike most other wines or liquors, there isn't enough alcohol in champagne to prevent it from actually freezing when placed inside a freezer. Freezing means expansion, and expansion—inside an airtight glass bottle—means a really bad day. Store champagne in the same way you would for a non-alcoholic carbonated beverage.
Salt lowers the freezing point of water, so if you're hoping to safely store—say—meat, all that salt is undoing the very freezing you're trying to accomplish. Salt not only increases the rancidity of meats (particularly fatty meats), but loses some of its flavor along the way. It's the worst of both worlds.
Milk sauces, like the one you might've made for a casserole or macaroni and cheese, will separate and then curdle when frozen, making the freezer an ineffective choice for long term storage of these delicious meals. You're better off just refrigerating for a couple days, or eating the entire pan in one night like I do.
Does anyone know a good dietician?
Canned Foods & Glass Storage Jars
Remember the champagne section? Again, freezing means expansion, and the resulting force is enough to break through an aluminum can and open the way for bacteria. Glass jars are even worse for obvious reasons. Nobody likes tiny glass shards in the same place they keep their food.
Whole Raw Eggs
Freezing raw eggs in their shell is a really bad idea. Best case scenario: The yolk and white expands, cracking the shell and permitting bacteria inside. Worst case: The yolk and white expands evenly and omni-directionally, finally cracking the shell all at once with explosive force, coating your freezer with egg and bits of shell. Don't freeze eggs.
Hey, at least you can still freeze a month's worth of Pizza Rolls no problem...
Hero image: Flickr user "penmachine" (CC BY-NC 2.0)