It is a firm, small block of a jelly-like substance made from Devil’s Tongue Yam powder, water and calcium-hydroxide (the chemical called “Lime.”)
It is used in Japan as a cooking ingredient, more for its texture than flavour. Yam Cake can be chopped up into chunks and added to hotpot dishes, or soups. Larger pieces can be grilled, then served with a sauce.
Yam Cake can be greyish or black, and come in different shapes. The dark is sometimes called “brown”, the greyish called “white.”
It is 90% water and is sold packed in water. It has a distinct, odd smell to it.
If working with chopped-up chunks of Yam Cake, simmer in boiling water for 2 minutes, then drain well.
If working with an entire block, roll it in salt, and let stand until it starts to weep. Then simmer the block in boiling water for about 3 minutes, drain, and let stand on a wicker or bamboo strainer. This also helps make the jelly firmer. After doing the whole block, you can then shred or tear it up. This allows flavours to better penetrate it.
Because Yam Cakes are so low in carbohydrates, some dieters in Japan simmer them in water, then mince them and mix them half and half with their rice.