After the food is swallowed, it passes through the oesophagus into the stomach. In the stomach it is thoroughly mixed with a digestive juice by a vigorous, to-and-fro churning motion. This motion is caused by contractions of strong muscles in the stomach walls.
The digestive juice in the stomach is called gastric juice. It contains hydrochloric acid and the enzyme pepsin. This juice begins the digestion of protein foods such as meat, eggs, and milk. Starches, sugars, and fats are not digested by the gastric juice. After a meal, some food remains in the stomach for two to five hours. But liquids and small particles begin to empty almost immediately. Food that has been churned, partly digested, and changed to a thick liquid is called chyme. Chyme passes from the stomach into the small intestine.