Authentic Kyushu brown rice vinegar accounts for less than 1 percent of Japan's annual 100-million-gallon vinegar production. During the Second World War, a shortage of rice encouraged the development of a much cheaper, quicker process. According to Togo Kuroiwa, author of Rice Vinegar, who spent most of his life trying to reestablish authentic rice-vinegar production in Japan, industrial rice-wine vinegar (sake cake vinegar) dates back to the early nineteenth century but became popular when the Japanese government rationed rice in 1942.
The quicker, industrial rice vinegar-making process does not use rice koji. Instead, it adds sake lees, the dregs left from sake manufacturing, to distilled grain alcohol. This mixture is fermented under controlled temperatures, and, in less than a month, bacteria convert the alcohol to acetic acid (distilled vinegar). Much more than flavor is lost in the sake lees-distilled alcohol process. Since the alcohol is distilled by boiling, most of the amino acids are left behind in the process. According to the Japan Food Research Laboratories, authentic rice vinegar has five times the amount of amino acids as sake-lees vinegar. What's more, it is the amino acids in vinegar that are most responsible for its medicinal powers.
When shopping for rice vinegar, read labels carefully. The highest-quality products are made from either brown rice or sweet brown rice and water. Although many Oriental foods store vinegars are half the price of natural food brands, keep in mind that these lower-priced products are invariably made from distilled alcohol and sake lees. Some brands list wheat, rice, corn, sake lees, and alcohol as their ingredients, while other brands list no ingredients at all. It is impossible to judge the quality of rice vinegar by its color, since some Oriental food brands have added coloring agents.
Ironically, the finest brand Kyushu vinegars, such as Maruboshi may contain a rice sediment, which, if disturbed, makes them look muddy. Rather then being a cause of concern, this sediment is a sign of quality.
Another type of Japanese vinegar , unrelated to brown rice vinegar, is called umeboshi vinegar or ume-su. Colorful and zesty umeboshi vinegar is a by product of making umeboshi, Japanese pickled plums.