Papain is a protease enzyme that can be added to beer before filtration and packaging. It was the first haze preventative used in the brewing industry. The enzyme is capable of digesting dissolved proteins—with amino acids as a by-product—and thus increasing the clarity of beer. One of the main natural sources of papain is unripe papaya fruit, which contains high levels of the compound. The enzyme can be purified by modern processing techniques and combined with other enzymes to produce specific mixtures suitable for chillproofing in brewing and other applications in the food industry. Among the many traditional uses of papain are as a meat tenderizer, as a medical aid on wounds and stings, and as a digestive aid. Meat wrapped overnight in crushed papaya leaves, for instance, becomes tender and requires less cooking time because of the release of papain in the milk-like papaya juice.
In brewing, papain is used to digest excess proteins after fermentation, because high protein levels can cause hazes, high viscosity, and excess foaming in the finished beer.