Perhaps this is just coming from a place of ignorance, but it seems to me like at the very least most East and South-East Asian cultures extensively use soy sauce in their cuisine. Did these cultures develop soy sauce independently? Did it come from somewhere and spread? Are there any cultures in the region that don't use soy sauce?
Good question. Soy sauce essentially originates in China, which spreads across East and Southeast Asia.
Soy sauce is derived from soybeans, which is believed to have first been cultivated by the early Chinese in the Zhou Period (11th-3rd Century BCE). Referred to as shu 菽 in Zhou texts and bronzes, soybeans and other legumes were a common food in North China, it proved a nutritious item as well as more stable to grow in adverse years. Soybeans are rich in digestible calcium, vitamins, iron, and importantly, protein, making it popular among the poor and peasant classes. Soy beans were eaten as a staple food alongside grains such as millet or wheat, in early periods they may have been eaten through simple preparations such as boiling and steaming, but because these are somewhat indigestible and unappetizing, they are commonly processed: ground or fermented. Over time, technology innovations allowed for more complex preparations and preservations of food. Thus derives tofu, bean curds, tofu skin, soy milk, imitation meat alternatives, salted beans, bean paste, etc etc, and of course, soy sauce, which appears in the late Zhou. Jiang 醬, a term often used in the modern day to refer to soybean sauces and pastes, appears in numerous texts from the Han Dynasty onwards, though in pre-modern China this does not necessarily refer to just soybean products. Instead it referred to various pickled and fermented meat and vegetable items, with or without the use of soybeans.
The general method to produce soy sauce is to ferment a mix of soy flour or beans and lightly ground grain with starter such as koji bacteria and salt, brining and refermenting it before straining it into a liquid. Soy sauce also helps to stretch salt, which may be expensive and costly for many. But early soy sauce may have resembled Ancient Roman garum, fermented with fish or meat.
Thus soy sauce and salted beans (chi/shi 豉) provides salt, nutrients, and taste to cuisine, making it popular among the general populace. Wu Zimu 吴自牧 reported in the late Southern Song:
"the things that people cannot do without every day are firewood, rice, oil, salt, soybean sauce, vinegar. and tea. Those who are just lightly better off cannot do without savory side dishes and soup. Though they be the poorest people, this must always be so."
It's beyond the scope of my answer and time to go country to country explaining how and why soy sauce arrived in each respective area. I'll say a couple things, such as for Japan. Soy and preparation methods/technologies were brought to Japan in successive waves in the 6th century, from political expeditions and Buddhist missionaries. The developing Japanese court interested in strengthening their power and prestige across Japan sought to adopt the sophisticated culture, technology, science, and religion of China, which then was considered the most advanced power in Asia. Thus, an array of things such as writing scripts, political systems, architecture, religion, philosophy, and in this case, cuisine and food production/preparation, came to be influence Japanese culture, with similar cases in Korea and Vietnam. That is to say of course, countries developed their own innovations and approaches towards all of these things. For example, a popular folk legend in Japan about the origin of soy sauce derives from a 12th century monk, Kakushin, who brought a bean paste production method from China. A kind of miso involving soy beans, rice, barley, and vegetables, in the fermentation process he noticed the dark liquid that trickled to the bottom of containers was quite edible and appetizing, and applied it for general cooking. Regardless by the 17th century Japanese producers were already developing their own soy sauces, such as tamari, which is derived from miso, a bean paste different from Chinese and Korea bean pastes. In other cases, while soybeans and soy sauce may have spread to other countries from China historically, much of the food we associate with cultures are relatively modern. Many Chinese immigrants, especially those from the Fujian and Guangdong regions of Mainland China, often spread throughout Southeast Asia in the early and late modern periods and have dramatically influenced cultures, especially in countries such as Thailand and Malaysia. A dish such as Pad Thai is actually a 20th century invention based on Chinese-Thai cuisine. Soy sauce obviously isn't a feature of say, Mongolian, Tibetan, or Central Asia cuisines, due to the differences in climate and environment. Nonetheless, soy sauce has historically and relatively recently spread from China to many South and Southeast Asian countries. It's mostly a staple item in China, Korea, Japan, and Vietnam, in other countries such as Thailand or Malaysia, it's often a phenomena of the large and influential Chinese communities residing there.
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