Maodu is the rumen part of cattle stomach, and cattle is a ruminant with compound stomach, which has four gastric cavities: rumen, reticular stomach, flap stomach and abomasum. The stomach wall of rumen consists of submucosal tissue layer, sarcolemma layer and serosa layer from inside to outside, of which sarcolemma layer is the most developed, consisting of two layers of smooth muscle, namely, the inner teres muscle and the outer longitudinal muscle, which is the main edible part of hairy belly. The flap stomach is actually a shutter. Because the layer inside the flap stomach is leaflike, it is called a hundred pages or a thousand layers of belly. In some parts of China, blind monks are also called hairy bellies.
The inner surface of rumen is the mucosa epithelium of mucosa, which is black and keratinized, and there are many reticular papillae, which directly affects the edible quality and must be removed. The methods of removing black film include hot water treatment, NaOH treatment, quicklime treatment, lactic acid treatment and citric acid treatment.
The consumption of beef omasum in China is mainly boiled vegetables represented by Chongqing hot pot. In early years, the riverside in Chongqing was a place for slaughtering cattle and sheep. All kinds of viscera are rich in nutrition and low in price, and the hairy belly can produce crisp and excellent taste with a little scalding, which is very popular with followers, so it became the main ingredient of hot pot at that time and is still one of the most sold dishes in Sichuan-Chongqing hot pot.