Changes

Also referred to as ''colloidal instability'', haze that forms after packaging in beer is often attributed to the interactions between polyphenols and proteins. Haze generally limits the shelf life of beer. Beer generally contains much more haze-active proteins than haze-active polyphenols. Haze-active proteins are acidic hydrophilic polypeptides that originate from barley and are rich in proline, glutamic acid, and glycosylated. Smaller phenols such as phenolic acids and flavonols do not contribute to haze, but heavier polyphenols such as procyanidin and prodelphinidin are strong haze inducers. These proteins and polyphenols combine and cause haze in beer. The polyphenol found in hops, catechin, does not form haze immediately but can cause haze after a period of storage. The pH has a huge impact on this reaction; much more haze is formed at a ph of 4.0 than it is at a pH of 3.0 or above 4.2. Higher ABV beers also encourage more haze formation from proteins and polyphenol reactions. This haze generally forms after a period of storage (called the "lag phase"); the longer this lag phase, the better the beer's colloidal stability. Haze can also be induced by oxidation, the presence of aldehydes, shaking, higher temperature, polyphenol-rich raw materials, light, and heavy metals <ref name="Callemien_2010" />.

Brewers generally remove haze by additives such as tannic acid, papain, or silica gel. Some of these additives can also remove foam forming proteins. Because of this, a chemical known as PVPP is often used because it does not remove foam forming proteins. Several products are available that contain combinations of PVPP and other compounds <ref name="Callemien_2010" />.