The abomasum breaks down dietary protein and prepares it for digestion by the small intestine. According to Colorado State University, this organ is found in cattle and is also known as the "fourth stomach," "glandular stomach" or "true stomach." Its function is similar to the single stomach found in humans and non-ruminant mammals.
The abomasum produces rennet, an enzyme complex that increases the bioavailability of dietary protein and is a crucial ingredient in cheese production. The lining of the abomasum contains the highest concentration of this enzyme. According to About.com Cheese expert Jennifer Meier, the finest rennet comes from the abomasa of slaughtered calves.
Most sections of the abomasum have an extremely strong flavor that is an acquired taste. It has several culinary applications. The most popular is lampredotto, a Tuscan specialty of thinly sliced abomasum boiled with vegetables and served on a hard roll. Those who prefer a milder meat flavor often make lampredotto with beef or tripe instead of abomasum.
Another specialty made with abomasum is the Korean makchang gui. This dish contains grilled abomasum and pork intestines, sliced onions and a savory sauce. The meat is first boiled in seasoned broth, which tenderizes it, removes most of the fat and makes the flavor much more delicate. After boiling, the meat is grilled with the rest of the ingredients and robed in sauce immediately before serving.