Haze is the broad term used for turbidity in beer; however, the term generally covers all forms of instability in beer in which insoluble material appears. As clarity is a desired trait in many types of beer, brewers of these beers work hard to avoid unwanted haze. Haze strictly refers to evenly distributed turbidity throughout the body of the beer, but there may be discrete particles (“bits,” “floaters”) that appear in otherwise “bright” beer. Precipitates and sediments may also appear, especially in bottle-conditioned or unfiltered beers.

From a technical point of view, there are several different types of haze. One form is so-called invisible haze (“pseudo haze”), which is caused by very small particles that cannot be readily detected by the eye but which scatter light in high intensity. Invisible haze is detected by haze meters that measure turbidity on the basis of the scatter of light at right angles to the incident. These “hazes” constitute a problem only insofar as they force the brewer to make a judgment on acceptability of the beer that contradicts what the instrument is saying. In other words, they present a logistical challenge. This is the reason why many brewers use haze meters that measure light scatter at a narrower “forward” angle, under which circumstances the spurious scatter is not registered.

Visible haze is differentiated into chill haze, which develops when beer is chilled to 32°F (0°C) but disappears when the beer warms to 68°F (20°C), and permanent haze, which is present at all temperatures. It is also differentiated into biological haze, which arises from the growth of living microorganisms in the beer, and non-biological haze, which is caused by a diversity of colloidally unstable non-living materials in beer. These materials include proline-rich polypeptides deriving from the storage proteins of grain, polyphenols (oxidized in the presence of transition metal ions such as iron and copper), starch, β-glucan, pentosans, oxalate, and dead yeast or bacteria.