After longer periods of storage, filtered beer loses its clarity and brilliance, especially when it is cooled, to the point that haze or a sediment layer forms in the beer. In order to eliminate sensitivity to cold and to avoid undesirable haze or turbidity, beer is often treated with clarifying agents, which allow beer to remain free of haze for months longer than it would without such treatment. Because it is valuable to gain some insight into the stability of packaged beer as early as possible, methods of analysis have been developed that provide information immediately after the packaging process regarding the propensity of a beer to form haze.
This analysis method can be performed quickly and provides an indication of the projected shelf life of a beer or the effect of a stabilizing agent, especially for purposes of quality control within a brewery. However, a linear relationship does not exist between precipitation with ammonium sulfate and the physico-chemical stability, since the latter involves other factors besides proteinaceous substances, e.g., tannin levels and the oxygen content of beer.
Beers of different composition yielding similar results for precipitation with ammonium sulfate may also exhibit a different shelf life [1–3].
Valid for all non-turbid beers
By incrementally adding increasing amounts of a saturated ammonium sulfate solution to beer, haze appears as a result of protein precipitation. The amount of the ammonium sulfate solution necessary to produce haze is directly proportional to the stability of the beer. The ammonium sulfate precipitation value expresses the ml of saturated ammonium sulfate solution that must be added to 100 ml of beer in order to produce a barely perceptible opalescence.