Glycine max

soybean

Glycine max (L.) Merr. (Fabaceae); sojaboon (Afrikaans); da hou, huang dou (Chinese); fève de soja, haricot soja (French); Sojabohne (German); kedelai (Indonesian); soia (Italian); daizu (Japanese); kacang soya (Malay); fríjol soya (Spanish); thua lueang (Thai)

DESCRIPTION Soybeans are fermented to make a wide range of condiments (sauces and pastes) that are characteristic of the cuisines of East and Southeast Asia. Soy sauce or shōyu (Japanese) is a salty, earthy, brownish liquid used for seasoning food during cooking or as table condiment and dipping sauce.1,2 It is produced by controlled fermentation of paste made from boiled soybeans (often with roasted and crushed wheat or barley added).1,2 Aspergillus moulds (A. oryzae, A. sojae) break down the soy and wheat proteins into free amino acids and the starch into simple sugars. Lactic acid bacteria ferment the sugars into lactic acid, while yeasts turn the sugars into alcohol. Ageing and secondary fermentation result in the complex flavour. After fermentation, salt and water are added. A quicker method to make soy sauce and other HVPs (hydrolysed vegetable proteins) is through acid hydrolysis.1

THE PLANT An annual with trifoliate leaves, minute flowers and hairy pods, each with up to four rounded seeds.

ORIGIN Wild soya (G. soja) is indigenous to East Asia and was domesticated in China around 1100 BC.3 Soy sauce started as a variant of fermented fish sauce but the two products eventually became separate entities. The making of soy sauce spread from China to Asia and later from Japan to Europe.1,2

CULTIVATION Soybeans are grown commercially on a large scale as an annual pulse crop.

HARVESTING Ripe pods and seeds are harvested mechanically.

CULINARY USES Soy-based products are a distinctive feature of Asian cuisines. These include soy sauce, soy paste (miso), soy curd (tofu or “soy cheese”), soy “milk” and fermented soy cakes (tempeh).1–3 There are numerous types of soy sauce (jeong yau) in China, e.g. light soy sauce (jeong tsing), an opaque, salty, light brown sauce used mainly for seasoning, dark soy sauce (lou chau), made by prolonged ageing and the addition of caramel colour and/or molasses, and thick soy sauce (jeong yau gou), a dark-coloured dipping and finishing sauce thickened with starch, sugar and spices. In Japan, there are five basic types of shōyu, which typically have a sweet and sherry-like flavour (koikuchi is the most common). In Indonesia, the term kecap and ketjap is used for all fermented sauces (the origin of the English word “ketchup”). These include kecap asin (salty, light soy sauce) and kecap manis (thick, sweet soy sauce with palm sugar or molasses added). Soy sauce is known as joseon ganjang in Korea, toyo in the Philippines, dóuyóu in Malaysia and Singapore and xi dau in Vietnam. Korean joseon ganjang and Japanese tamari are dark, rich liquid by-products formed when fermented soybean pastes (Korean doenjang and Japanese miso) are made.

FLAVOUR COMPOUNDS Soy sauce adds an umami (savoury) taste to food because of the presence of glutamic acid and other glutamates. Glutamic acid is an abundant naturally occurring amino acid, used as food additive in the form of the sodium salt (monosodium glutamate or MSG).

NOTES Soy sauce was the original secret ingredient of Worcestershire sauce,2,3 later replaced by HVP.

1. Tanaka, N. 2000. Shōyu: the flavour of Japan. The Japan Foundation Newsletter 27: 1–7.

2. Shurtleff, W., Aoyagi, A. 2012. History of soy sauce (160 CE to 2012): extensively annotated bibliography and source book. SoyInfo Center, Lafayette.

3. Mabberley, D.J. 2008. Mabberley’s plant-book (3rd ed.). Cambridge University Press, Cambridge.