Probably the healthiest of all proteins, and easily digestible by all ages, the soy bean - known in Cantonese as dai dau ('great bean') - has provided taste and nutrition in China for centuries. Beans are processed in numerous ways. If they are spread on water-filled trays and sprouted under lights, nga choy ('nail vegetable') or bean sprouts result. Fresh soy bean pods, prepared much like snow peas, are a popular vegetable. Dried mature beans are soaked then ground to make dau cheung ('bean milk'), or slightly curdled then settled with gypsum to make dau foo ('bean curd', or tofu; below right). Dau foo pei ('bean curd skin'), the scum that forms on heated bean milk, is dried and used as a wrapper for various foods or cut up and incorporated into vegetarian dishes. Alternatively the beans can be fermented to make various kinds of dau see ('fermented beans') and dau cheung ('bean sauce'), small quantities of which are mashed up and added to garlic, oil and sometimes shallots or chillies to produce a tasty condiment. Soy sauce - an early Hong Kong export commodity - comes in various grades. The thin, light-coloured variety, produced from the first pressing of the beans, is known as sang chau ('fresh extraction') while the thicker, darker kind is see yau ('bean sauce'). Indonesian-style soy sauce, known as kecap manis, is thickened and sweetened with palm-sugar syrup. Yau Ma Tei and Wan Chai in the 19th century were known for their soy-processing shops, and a few small businesses producing sauces and pastes still survive. Yuen Long was known for its soy-bean processing. Fermenting vats of beans and sauce truly stink and for this reason factories that processed the bean were usually located in remote areas, as Yuen Long once was. Millstones used to grind bean curd can still be found abandoned in villages across the New Territories. Beancurd was a staple dietary item in Buddhist nunneries, where it was often sold too. Women who chose to be single were sometimes - and still are - the subject of prurient gossip; consequently the expression mor dau foo ('grind bean curd') evolved into a vulgar Cantonese euphemism for lesbianism. Soy beans are produced in massive quantities all over the world, principally in the US, Australia, Canada and Brazil. Alas, most don't directly feed human beings; much of the world's soy is processed for animal feed.