This article is from the Vegetarianism FAQ, by firstname.lastname@example.org (Michael Traub) with numerous contributions by others.
Miso is made from fermented soybeans, and usually is found in a
paste form. It is used as a flavouring agent, and for soup stocks.
Storing Miso: If it is a dark miso, like hatcho miso, or red miso,
it will keep for a while unrefrigerated, especially if it is 3
year miso. However, it does not hurt to refrigerate it. If it is
sweet miso like yellow, mellow white, or sweet white, it will not
keep unless refrigerated. Also, if the miso has been pasteurized,
it should be kept refrigerated. Warning! Some Japanese brands of Miso
contain fish stock!
Nutritional value, per tablespoon:
calories 36 g.
protein 2 g.
carbs 5 g.
fat 1 g.
sodium 629 mg.
(from Pennington, "Food Values of Portions Commonly Used")