Soy sauce comes in both light and dark varieties. Light soy sauce comes from the first pressing, tastes rather salty, and is the most common type of soy sauce. Dark soy sauce is fermented for a longer time and often has added caramel or molasses. It is less salty, thicker, and slightly sweetish in taste.
From Wikipedia: “Soy sauce (also called soya sauce) is a condiment made from a fermented paste of boiled soybeans, roasted grain, brine, and Aspergillus oryzae or Aspergillus sojae molds. Soy sauce in its current form seems to have begun in the 2nd century AD in China and spread throughout East and Southeast Asia where it is used in cooking and as a condiment.”
“Soy sauce is made either by fermentation or by hydrolysis. Some commercial sauces have both fermented and chemical sauces.
Flavor, color, and aroma developments during production are attributed to non-enzymatic Maillard browning.
Variation is usually achieved as the result of different methods and durations of fermentation, different ratios of water, salt, and fermented soy, or through the addition of other ingredients.”
Detailed information about traditional and industrial produced soy sauce is provided by the abovementioned Wikipedia link.
“A study by the National University of Singapore showed that Chinese dark soy sauce contains 10 times the antioxidants of red wine, and can help prevent cardiovascular diseases. Soy sauce is rich in lactic acid bacteria and of excellent anti-allergic potential.
Soy sauce does not contain the level of isoflavones associated with other soy products such as tofu or edamame. It can also be very salty, having a salt content between 14–18%. Low-sodium soy sauces are made, but it is difficult to make soy sauce without using some quantity of salt as an antimicrobial agent.”
Soy sauce and “raw food”:
We don’t consider soy sauce to be raw. Soybeans are generally heated during the production process since they like all other green beans contain the glycoprotein phasin, which is toxic for humans. Phasin inhibits the absorption of nutrients in the intestine, causes hemagglutination (clumping of the red blood cells), and in larger amounts can destroy the intestinal villi. Heating processes (e.g., cooking and roasting) destroy phasin, making soybeans and soybean products such as tofu, miso, and tempeh safe for human comsumption. As a result, even unpasteurized soy products are not actually raw, but are instead cooked products that have been “revived” through the process of fermentation.
“In 2001, the United Kingdom Food Standards Agency found in testing various soy sauces manufactured in mainland China, Taiwan, Hong Kong, and Thailand (made from hydrolyzed soy protein, rather than being naturally fermented) that 22% of tested samples, contained a chemical carcinogen named 3-MCPD (3-monochloropropane-1,2-diol) at levels considerably higher than those deemed safe by the EU. About two-thirds of these samples also contained a second carcinogenic chemical named 1,3-DCP (1,3-dichloropropane-2-ol) which experts advise should not be present at any levels in food. Both chemicals have the potential to cause cancer and the Agency recommended that the affected products be withdrawn from shelves and avoided. 3-MCPD and 1,3-DCP. The same carcinogens were found in soy sauces manufactured in Vietnam, causing a food scare in 2007.
In Canada, the Canadian Cancer Society writes, "Health Canada has concluded that there is no health risk to Canadians from use of available soy and oyster sauces. Because continuous lifetime exposure to high levels of 3-MCPD could pose a health risk, Health Canada has established 1.0 part per million (ppm) as a guideline for importers of these sauces, in order to reduce Canadians' long-term exposure to this chemical. This is considered to be a very safe level.”
“Most varieties of soy sauce contain wheat, to which some people have a medical intolerance. However, some naturally brewed soy sauces made with wheat may be tolerated by people with a specific intolerance to gluten because gluten is not detectable in the finished product. Japanese tamari soy sauce is traditionally wheat-free, and some tamari available commercially today is wheat- and gluten-free.”