Beer Clarity part 1
Beer is subject to colloidal instability during storage. Chill filtered beer initially remains haze free, however, as the product ages it passes through a series of metastable colloidal states, whereby chill hazes and eventually insoluble (permanent) hazes form, primarily as a result of protein-polyphenol interactions within the product. Haze reactions are significantly accelerated with increasing temperature, due to an increase in the rate of reactions (Kunze, 1999).
Proteins and polyphenols are natural components of beer which are extracted from malt and hops. Haze active (HA) proteins contain high percentages of the amino acid proline and are thought to be the degradative products (as a result of the malting and brewing process) of barley hordein. Globulin and albumin proteins are also regarded as haze active, as they associate with polyphenols in the beer to form hazes upon removal of the proline containing proteins.
The polyphenols primarily involved in haze formation are barley flavanoids such as catechin, or polymers of the latter, proanthocyanidins.
The mechanism of haze formation is the following: Haze active proteins contain a number of active sites, thought to be the proline residues, which have a specific affinity for polyphenols. If polyphenols have two binding ends, they are capable of linking protein molecules together, forming colloidal particles, which create haze. Smaller colloidal particles initially form in beer, as there are insufficient amounts of polyphenols to link any more than two protein molecules together, hence light hazes form. Larger particles and increased haze can form when polyphenol levels approach those of the protein (due to oxidative reactions during storage ), as polyphenol linking of the proteins can form large networks.Tags:beer beer clarity