Soya beans and soy beans:
Are exactly the same and the names are used interchangeably according to fashion, preference or habit. The many subsequent products, such as soya/soy sauce, are also exactly the same, whichever spelling is used.
Shoyu is the Japanese word for the same vegetable and its products – shoyu sauce is soya/ soy sauce.
The vital claim of the soya bean is that it is the only vegetable product that has all the protein content of meat, eggs or milk products and thus it’s essential to the diet of vegetarians and vegans. The beans themselves are bland and generally unappealing as they never quite develop the rich, meaty textures that other beans do with long cooking.
Thus mature soya beans are used to make tofu, which is a soft or firm curd made from the milky liquid obtained by boiling and pressing soya beans and which retain the full protein content. Young, green soya beans are much more appealing to eat and marketed widely as edamame.