Curious about those packets of brown fluid that come with your Chinese takeout? For over two thousand years the Chinese have been fermenting soybeans. Two foods are derived from this fermentation: miso, which is a paste used in soups and sauces, and soy sauce. From China soy sauce spread all over Asia, and is known as "shoju" in Japan. There are many, many types of soy sauce today, and it has increased in popularity in the West. Despite the differences, true soy sauce has an earthy, salty taste, akin to what the Japanese call "umami."
Traditionally, soy sauce was fermented in huge urns in the sun, often for up to three years. It is then processed much like wine: filtered, blended, and aged. Now it is commercially prepared in machines. Cheaper brands of soy sauce use hydrolyzed soy protein instead of the brewing process, and are popular because of the price. In the West these brands are sometimes called liquid aminos (Bragg makes and sells bottles of this.) Some artificial soy sauces can be carcinogenic, so they should be avoided in general. Besides soybeans, the fermenting process includes yeast and sometimes a grain, most often wheat, barley, or rice.
Chinese soy sauce comes in basically two versions: light and dark. The light is from the first pressing of the soybeans, and is more expensive, just like the first pressing of olive oil, because of its superior taste. There are further delineations, but most soy sauces in this category are used to season dishes, because it is saltier but doesn't affect the color of the dish, or in dipping sauces. Dark soy sauce is aged and less salty but sweeter. It is used in cooking for its ability to color a dish as well as for taste.
Japanese soy sauce is thought to have been brought to Japan by Buddhist monks. Shoju is made of soybeans, wheat, brine, and a yeast, known as koji, which is also used to ferment sake. Shoju is found in five traditional categories and two newer ones, based on how they were made and the ingredients used. They cannot be used in place of each other because of their differences. The Japanese use wheat as a grain, which gives a sweeter taste, and sometimes they add alcohol. Koikuchi is a dark sauce made of half wheat and half soy. It is the most common Japanese soy sauce, and counts for most of their production. Tamari is darker and more flavorful and contains little or no wheat, so it is perfect for those with wheat intolerance. This is the closest to the original Chinese soy sauce. Shiro uses mostly wheat, which gives it a light taste and color. Saishikomi is twice brewed, which means koikuchi sauce is used instead of the normal brine. Finally, usukuchi is very salty and light in color, due to the use of a liquid made of fermented rice, called amazake, which also makes it taste sweet. Two newer types are amakuchi, a variant of koikuchi, which is also called Hawaiian soy sauce for its sweet flavor; and genen, which is lower in salt content.
The Japanese are very serious about soy sauce, and have special terms for both the quality of a sauce, and the method of production. There are three categories of quality: hyojun, or pasteurized; tokkyu or unpasteurized; and tokusen, the highest quality and limited quantity. There are two other terms used to describe soy sauce: chotokusen, which indicates the best; and hatsuakana refers to industrial grade sauce, mostly used for powders and flavoring.
Korean soy sauce is called joseon ganjang. Used very little by the Koreans, who seem to prefer Japanese soy sauces, it is thin and dark, made of soy and brine. The Taiwanese are renown for their black bean soy sauce, which takes longer to produce. They also produce a soybean and wheat sauce.
Other Asian countries produce soy sauces, but none are well known except for Malaysia, which makes kecap manis, a thick sauce sweetened with palm sugar, garlic, and anise. Because of Malaysia's ties with Indonesia, they use the same name for their soy sauces - kecap, which is the basis for our word ketchup. Kecap asin, kecap manis, and kecap manis sedang are all Indonesian soy sauces. Kecap inggri, or "English sauce" is their name for Worcestershire sauce, and kecap ikan is fish sauce, although both of these are usually placed under the soy sauce category.