Rice vinegars are distinctive because they contribute a sour, vinegar flavour while remaining quite mild and pleasant, especially when compared to distilled (white) vinegar. Substitutions must therefore take the flavour into account, and not simply the acidity.

Japanese rice vinegars are, generally, milder tasting than Chinese ones.  Korean rice vinegar is often even milder tasting than Japanese.  Taiwanese rice vinegars may be made in a Chinese or Japanese style.  Unless you're using very large quantities of vinegar, the differences in strength aren't generally going to be enough of an issue to necessitate having multiple different types on hand for your cooking.  If you're making a Korean or Japanese dish that calls for a lot of rice vinegar and you find that yours is a bit too harsh, try diluting it just a bit with water and a tiny bit of sugar.

If you haven't got any rice vinegar at all, you can substitute other flavoured vinegars (e.g. white wine, champagne, or apple cider) at about 3/4 strength, diluted with water if necessary. You can also substitute half the volume of white vinegar mixed with an equal volume of water and a small amount of sugar (to taste).  It's important to note that these won't taste like rice vinegar, but they will work in much the same way in a recipe (like substituting lemons for limes).

In general, I don't recommend substituting with the various specialty rice vinegars (e.g. Chinkiang vinegar, red vinegar, black vinegar, etc.) unless you're quite familiar with their flavours and properties.  For example, Chinkiang vinegar and Japanese black vinegar can be substitute for one another quite easily, but neither is a particularly good substitute for regular rice vinegar.

JAPANESE VARIETIES

Komezu or kome-su (米酢) (pronounced ko-MAY-zu) – Common and widely used in the West, this pleasant, mildly sweet, flavourful variety lends itself not only to Japanese cuisine, but also to salads, pickles, and a wide variety of other cuisines.  When a recipe calls for rice vinegar, it’s generally safe to assume that you can use the Japanese version (or the very similar Taiwanese versions).

Komezu may actually be made with some grains in addition to rice.  In Japan, junmai-su refers to vinegar made only with white rice, while genmai-su refers to vinegar made with brown rice.  Genmai-su has a deeper, somewhat richer flavour than junmai-su.  Kuro-su, literally black vinegar, is a specialized rice vinegar from southern Japan.  It has a deep, rich, savoury flavour, and, like the specialized Chinese vinegars, should generally be used when called for and not as a substitute for standard rice vinegar.

KOREAN VARIETIES

Ssal sikcho (쌀식초) – That being said, a mild, basic rice vinegar is standard for Korean cooking.  Like the Japanese varieties, Korean rice vinegar comes in white rice (chapssal – 찹쌀) and brown rice (hyeonmi – 현미) varieties.  Korean rice vinegar tends to be extremely mild tasting, even more so than Japanese vinegar.  When cooking Korean food, be sure to use rice vinegar when actually specified by the recipe, as apple-based vinegars are also commonly used. Mild, often fruity rice vinegar called micho (미초) is actually a very trendy health drink in Korea, so don’t be surprised to find a wealth of fruit, spirit, and grain vinegars in a Korean market.  These types are generally not meant for cooking with however, and aren't meant for substituting with basic ssal sikcho.

VIETNAMESE VARIETIES

Giấm gạo or dấm gạo – In addition the basic, mild ‘plain’ rice versions, there are several specialized varieties of Vietnamese vinegar that feature spice or varying levels of sourness, but these are not widely used and tend to be very hard to find outside of Vietnam.  In general, one can substitute a Chinese or Japanese variety when rice vinegar is called for in a Vietnamese recipe.

CHINESE VARIETIES

Mǐcù (pronounced Mee-tsu) – Chinese rice vinegars are subdivided into many different varieties, each with a distinct flavour profile.  Chinese cooking generally does not consider these to be interchangeable, preferring to use each one for specific dishes and cuisines.  If a recipes simply calls for rice vinegar, use a 'plain' mǐcù variety, and not a specialized one from the list below.  If you can’t find a basic Chinese rice vinegar, substitute a Japanese one – the flavour may be somewhat milder, but unless you're using very large quantities, the overall effect on the dish shouldn't be too noticeable.  Consider adding a small quantity of white vinegar if you feel that you need a stronger, more acidic taste.

A list of some of the more important specialty varieties is given below. I hope to treat these separately in future Pantry Pages.

• Chinkiang/Zhenjiang Vinegar (鎭江香醋) – a strongly flavoured black vinegar, often containing wheat, millet and/or sorghum in addition to rice.  Note that Northern Chinese black vinegars (for example 老陳醋, aka "mature vinegar" and 山西老陈醋,
  aka "Shanxi vinegar") are sorghum based, and generally doesn't contain any rice.
• Red Rice Vinegar (大紅浙醋) – a common accompaniment to seafood dishes, this vinegar is traditionally made from rice fermented with a special red fungal culture.  Inexpensive substitutes are generally made with regular rice vinegar dyed red.  This variety is actually somewhat similar to plain rice vinegar in terms of flavour, though the colour will obviously impact a final dish.  Naturally brewed red rice vinegar tends to be a brownish red, while the artificially dyed ones are generally a very vivid red.
• Sweet Vinegar (甜醋) – a Cantonese specialty, this flavourful black vinegar from Southern China has a strong and very sweet flavour.  These days, the variety is practically synonymous with the Pat Chun Sweet Vinegar brand (八珍甜醋).
• Baoning Vinegar (四川保宁醋) – a dark, strongly flavoured vinegar from China's Szechuan region, made from glutinous rice and wheat.  Baoning vinegar is similar to Chinkiang vinegar.