European chefs in the 18th century tried to copy soy sauce with mushrooms and spices, and failed, because it has to be fermented rather than simply cooked. This episode traces soy sauce back roughly 2,200 years to Han dynasty China, when expensive salt was stretched by fermenting it into jiang paste. The dark liquid that pooled on top of the soybean version became soy sauce, and Buddhist monks later carried the method to Japan and Korea.

We explain how the koji mold Aspergillus oryzae breaks proteins down into glutamic acid, how lactic acid bacteria and yeast then take over in the moromi mash, and how slow Maillard browning darkens the sauce without heat. The episode compares traditional high-salt brewing with faster low-salt methods, a 72-hour Soviet process, and acid-hydrolyzed sauce. It also tours regional styles and weighs the health factors, from antioxidants and probiotics to sodium, 3-MCPD and gluten.

• How soy sauce began as a way to stretch expensive salt
• The two microbial stages of traditional soy sauce brewing
• Chinese light and dark soy, Japanese koikuchi and tamari
• Indonesian kecap manis, Korean ganjang, and Filipino toyomansi
• Why 14 to 18 percent salt protects the fermentation from spoilage