beef lung
The lung of the cow, an offal with loose, spongy tissue that turns soft and slightly springy when cooked and tastes mild.
Beef lung is an offal with airy, porous tissue that is strikingly light when raw and floats on water. Cooked, it becomes soft, a little springy and fibrous, with a mild taste less assertive than liver or kidney. Because it soaks up a lot of liquid, it suits braises and spiced sauces, where it takes on the flavours around it. It is usually parboiled in water first, after which the windpipe and cartilage are removed and the meat is cut small. It is rarely on display but can often be ordered from a butcher, including Turkish and other halal butchers in Europe. Make sure you buy lung sold for human consumption rather than as pet food; in the United States, lung is not permitted for sale as human food.
Substitute:
There is no true substitute, because no other offal has the same spongy, absorbent texture. Beef heart comes closest, being similarly mild, but it stays noticeably firmer and more muscular; in mixed offal dishes you can replace the lung with heart and accept a denser, chewier result. Liver is less suitable, as it tastes stronger and cooks differently.