Important process step in the brewery, on which the shelf life and the appearance (i.e., clarity and brightness) depend. Continuous monitoring of filtration is crucial, because immediately after this treatment step the beer is kegged, bottled or canned and then shipped.
Both shelf life and appearance are impaired by the presence of protein/tannin colloids, yeast cells, and filtration auxiliary particles. Because all of these substances create scattered light, they are susceptible to detection by photometric turbidity measurement.
Sigrist has been equipping filtration equipment with turbidimeters for over 50 years.
Originally all such instruments used the 90° scatter angle.
Later it was found that the protein/tannin colloids create most of the scattered light at
this angle. The yeast cells and filtration auxiliaries, on the other hand, have a larger particle size and therefore scatter the light forwards (i.e. at a
smaller angle) to a much greater extent. Armed with this knowledge, Sigrist developed a
combined dual-angle instrument, which detects the turbidity
alternately at 90° and 25° and delivers two readings continuously. This tells the brewer
which components are causing the turbidity, so that appropriate corrective action can be
Turbidity of a yeast suspension.
Turbidity of diatomaceous earth at various scatter angles