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Trans-2-nonsnal, 3-hydroxynonanal and 3-hydroxybutanal were isolated from barley and wort and mass spectral evidence for the presence of further hydroxyaldehydes was found. The concentration of free aldehydes in a model solution was found to decrease in the presence of bisulphite. Addition of acetaldehyde to a mixture of aldehyde bisulphite complexes released trans-2-nonenal in preference to other aldehydes.The concentration of sulphite in beer decreased by 66% over four months. This data was combined in a theory in which the papery, cardboard stage of beer staling is ascribed to a decrease in bisulphite concentration and subsequent bisulphite transfer from unsaturated aldehyde bisulphite addition complexes.

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