There are many varieties of miso. A brief description of the more common varieties are explained here...
Miso [me-soh], is traditionally made in Japan. There are many variations of miso, which are basically all made from koji mixed with either rice, barley, and/or soy beans. The ingredients are fermented and aged in crocks or wooden kegs. Some of the lighter sweet miso, such as Shiro miso, are aged for only one to two months. While the darker varieties, such as Hatch miso, may be aged for up to 2 years. Miso comes in many colours, ranging from creamy white, red and cocoa-brown, and variations. The texture and taste of these variations are just as diverse. Some varieties are made solely from either rice, barley or soy bean, or a mixture. Miso is believe to have originated in China [or Korea?] where it is known as Chiang or soybean paste.
Shiro Miso (Kyoto Shiro Miso, or Saikyo Miso) or young sweet white miso has a delicate sweet smooth flavour and texture. Shiro Miso is made by combining up to 4 parts of rice to 2 parts of soybeans to 1 part salt. Shiro miso may range in colour from bone white to light yellow. Shiro miso contains the lowest salt content of all miso. This form of miso has a hint of a sake-like flavour, due to alcohol produced during fermentation, which is retained in the finished miso. This is also due to the short fermentation process, which helps to preserve the finished miso, adding a well rounded flavour to the finished product. Shiro Miso is manufactured commercially using a special complex process. This process is apparently a well guarded secret by its manufacturers in Japan.
Kome miso, is mainly a brown rice miso,
red in colour and is
also known as "red miso" [Aka miso]. Kome miso has the highest
salt content of all miso and has a thick rich creamy texture.
Mugi miso is a
barley miso, darker than rice miso and also
aged longer. It also has a creamy texture and a red brown colour.
Hatcho miso is Japans most favourite miso, prepared from soy beans and soy koji. It is chunky, dark chocolate brown in colour and high in protein. Hatcho Miso is prepared from cooked soy beans, which are cooled and mixed with the mother-culture koji and salt. The mixture is fashioned into round balls which are placed in wooden barrels, pressed under weight and left to aged for up to 18 months. During this time, the enzyme-rich koji breaks down the protein and starches into amino acids and lactic acid. The finished miso has a dark brown-black colour, a salty flavour with a hint of sourness with an aftertaste which is dependent on the master's trade-secret.
Name miso is made solely from soy beans. Traditional methods for preparing name miso is quite different compared to most other miso, as wild mold spores were forced to grow on cooked, crushed soy bean balls [miso-dama] wrapped in rice straw and usually left to hang indoors near a wood-oven until mold-growth covers the beans [approx. one month]. The beans were mashed, mixed with salt and water, then fermented and aged in crocks or kegs. Natto Miso is sometimes confused with natto. Natto miso is prepared with koji. However, natto is prepared with soybeans cultured with a specific bacteria. Unlike natto, natto-miso contains salt and is prepared with whole barley and soybean Koji, Hijiki or Kombu seaweed and ginger.
Reference - Shurtleff, W.; A. Aoyagi  The Book of Miso. Autumn Press, Kanagawa-ken, Japan
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