part 1 of this can be found Beer Clarity part 1
continuing our article on Beer Clarity and hazes
Chill hazes consist of small (0.6µm) particles and are a result of HA protein-polyphenol (catechin) cross linking, via hydrogen or hydrophobic bonding, at temperatures of 0 – 4°C. Such hazes re-dissolve upon warming to 20°C as these bonds are weak; however, polyphenols such as catechin are subject to oxidation during beer storage, producing polymers, which form large particles (1 – 10µm) and permanent hazes when covalently cross-linked with HA proteins.
Beer haze is typically measured via nephelometric methods, which are based upon the principle of light scattering when a beam of white light passes through a solution carrying a dispersion of particles (Fischer, 1966). The size, concentration, shape and differing refractive index (compared to the media) of the particles dictate the amount and intensity of the light scattered over a range of angles. Increasing amounts of particles (haze) in the medium corresponds with increased capacity to scatter light. Nephelometric instruments primarily measure the intensity of light scattered at a 90° angle from the incident beam. Measurements at narrow angles, i.e. 13°, are sensitive to large particles (1 – 10µm) that often form visible hazes, whereas 90° angles are sensitive to pseudo or invisible hazes that form from smaller particles < 0.1µm. Larger particles are (usually) removed during the filtration of beer, but smaller particles may remain in the final product to promote colloidal instability. Thus, beer haze measurements are usually performed at 90° angles.
Large, modern commercial breweries address the problem of protein-polyphenol colloidal instability via the use of adsorbents during beer filtration, such as silica gels, which bind to HA proteins, or Polyvinylpolypyrrolidone (PVPP), which binds to HA polyphenols. Both compounds are highly selective for their respective HA material.Tags:beer clarity beer haze