Sweet, mild rice wine vinegar -- or simply "rice vinegar," as it's also often labeled -- lends a delicately tart flavor to many Asian dishes. Brewed like sake from fermented rice, it has no direct equivalent among Western ingredients. Still, if you're making a recipe that calls for rice vinegar, a number of other vinegars can make satisfactory substitutes. The end flavor will be slightly different, though you can minimize that effect with a few simple tweaks.
White Wine Vinegar
Western-style white wine vinegars have a pale color, like rice vinegar, but they tend to be stronger, more acidic and less nuanced than rice vinegar. Start with a good-quality, well-aged white wine vinegar if you can, because they're mellower. Use less than the recipe calls for, or dilute the wine vinegar with water or other liquids. Rice vinegar is slightly sweet, so you might need to add a pinch of sugar, a few drops of honey or agave syrup, or any other sweetener that appeals to your taste buds.
Other Wine Vinegars
Other wine vinegars often make useful substitutes for rice vinegar, most notably champagne vinegar, sherry vinegar and white balsamic. Champagne and sherry vinegar, like white wine vinegar, vary widely in quality. Young, rough versions must be diluted to serve as substitutes for rice vinegar, so older, mellower bottles are preferable. White balsamic vinegar is something of a marketing gimmick, lacking the subtlety of true balsamic, but it's also a passable option. All of these vinegars should be sweetened slightly, though white balsamic -- which has some sweetness of its own -- requires less.
Apple Cider Vinegar
Although apples and rice couldn't be more unlike as ingredients, apple cider vinegar has something of rice vinegar's aromatic complexity. As with wine vinegars, apple cider vinegar is typically stronger and sharper tasting than rice vinegar, so it must be lightly sweetened and diluted to serve as a suitable replacement.
Just Add Wine
For a flavor that approximates rice vinegar more closely, consider using a splash of rice wine -- rather than water -- to dilute a Western-style vinegar. Either a Chinese-style rice wine, such as Shaoxing wine, or a Japanese-style sake is appropriate. Mirin, a sweetened Japanese rice wine, is an even better option because of its sugar content.
The Red and the Black
A recipe simply calling for "rice vinegar" or "rice wine vinegar" invariably means the pale white variety, but there are two others you might encounter. One is a red rice vinegar, used in sauces or for dipping. Substitute a mellow red wine vinegar or malt vinegar, lightly sweetened and salted to replicate the original. Black rice vinegar is a common dipping sauce for dumplings and other foods, with a bolder flavor than the white kind. If your pantry is well-stocked, use a mixture of 3 to 4 parts sherry vinegar and 1 of balsamic vinegar for a reasonable approximation of its taste.