After fermentation the temperature is lowered and the beer is maturated for a period during which the off-flavour component diacetyl is assimilated by yeast cells. Mature beer is then chilled to a temperature of -2 oC for a couple of days. By doing so the colloidal stability of the beer is greatly improved due to precipitation of protein-tannin complexes, which are only sparingly soluble at low temperature. The beer is now ready for final stabilisation, which removes further amounts of proteinaceous matter and/or tannins, and subsequent filtration. The bright beer so obtained, and adjusted to the correct carbon dioxide content, is now ready for bottling.
When the residual yeast cells have been removed it is of utmost importance that oxygen uptake is reduced as much as possible, since oxygen will damage the flavour stability of the beer and, despite intensive stabilisation, also impairs its colloidal stability.