Vegetable pepsin is another name for papain — the protein-digesting enzyme extracted from the latex of unripe papaya fruit. The old-fashioned name reflects its use as a plant-derived equivalent of pepsin, the stomach’s own protein-digesting enzyme: it breaks down tough meat proteins, which is why papain is the active ingredient in many commercial meat tenderisers and a traditional marinade component in tropical cuisines. It also appears in brewing, where it prevents chill haze by digesting haze-forming proteins, and in digestive-aid supplements. Like all enzymes it is inactivated by high heat, so its tenderising work happens before or during the early stages of cooking.