The main component of gastric juice varies between several substances; it is made of pepsin, rennin, hydrochloric acid, mucus, amylase and water. The first three constituents are the primary digestive agents; pepsin breaks down complex proteins into simpler forms while rennin specifically deals with milk proteins.
The mucus makeup of gastric juice protects the lining of the stomach from the acidic environment; the hydrochloric acid is found in solutions of approximately 0.5 percent, creating a pH between 1 and 3. The highly acidic content of the stomach inhibits and destroys bacterial growths that are associated with eaten food. The enzyme amylase, which is produced in the saliva, travels down to the stomach and helps in digesting carbohydrates.