ice
Frozen water. In cooking it functions less as a food and more as a temperature-control tool -- it chills drinks fast, and shocking hot, just-blanched vegetables in ice water stops their cooking instantly so they keep their color and crunch.
Buying guidance
Any ice works, but if tap water tastes strongly of chlorine or minerals, cubes made from it can flavor a drink faintly; filtered water makes cleaner-tasting ice for cocktails and iced tea. For an ice bath, use plenty of ice to a little water -- a bowl that's mostly water with only a few cubes floating in it won't stay cold enough to actually stop the cooking.
Substitutions
- Very cold water in a bowl chilled in the freezer beforehand -- works for simple chilling but won't shock-stop cooking vegetables as fast as true ice.
- Frozen gel packs placed around a container -- chills without diluting a drink, but is not a substitute for an ice bath's rapid cooling.
Storage
Ice left uncovered in an open bin or tray absorbs odors from other freezer contents surprisingly easily -- keep it in a closed container, and dump out and remake a batch that's been sitting for weeks if it starts tasting stale or freezer-flavored.