The liquid is produced by soaking dry soybeans, and grinding them with water. Soy milk contains about the same proportion of protein as cow's milk~ around 3.5%; also 2% fat, 2.9% carbohydrate and 0.5% ash. Soy milk can be made at home with traditional kitchen tools or with a soy milk machine. source: wikipedia.com

Soya Milk: ½ pint dried Soya Beans 1 Gallon Water Soak the beans in water overnight. With an excess of water, liquidise the beans to form a light slurry. Make up to 1 gallon. Quickly bring to the boil and boil for only 20 minutes (if you boil longer, it will curdle and this is not the correct time to start the cheese process). Cool quickly and filter the milk through muslin or cheese cloth. Making your own Soya Milk involves boiling around a gallon of water and, as a result, is quite hazardous. Boiling such a large quantity on a domestic cooker is not particularly efficient (or green)and is also time consuming. Making Tofu is also time consuming, involving a pressing process and after you have taken the trouble to make your gallon of soya milk, you may find it difficult to come to terms with the fact that you are going to curdle it. My advice is, unless you really want to make these (it is always good to have a go at least once and then, if you really need to, you are not forced to experiment), or have no alternative, buy them in the shops (unless they are ripping you off of course). Boiling a gallon of milk and then cooling it down quickly (so as to avoid curdling) is done far better with the heat efficient large vessels and counter-current heat exchangers that you find in the commercial process.