High molecular weight proteins are quantified in the determination of coagulable nitrogen in wort and beer. If the amount of coagulable nitrogen compared to the amount of total nitrogen in beer is low, this can affect body, foam stability and colloidal stability.
With particular regard to satisfactory protein stability in beer, there should not be an excess of coagulable nitrogen; alternatively, a minimum level of coagulable nitrogen is necessary for good foam stability. For these reasons, an exact knowledge of the coagulable nitrogen content is desirable, not only for evaluating brewhouse procedures, but also to provide valuable information as to whether an adsorbent, precipitating or degrading protein stabilization aid should be utilized for clarification of the beer.
Earlier, coagulable nitrogenous substances were precipitated by boiling for five hours in a saturated salt (sodium chloride) water bath. Since this method was very tedious and cumbersome, the use of a glycerin bath has since been adopted. However, when boiling at the same temperature of 105 °C, the glycerin bath produces a less intense boil and lower values for coagulable nitrogen.
By adding sodium dithionite to the wort, the protein coagulates much faster and the precipitation achieved is much more uniform even if the intensity of the boil is not constant. In beer, the precipitation is reduced by boiling at excessive temperatures. If one wishes to avoid the use of a liquid bath (saltwater bath 105 °C), the determination can be carried out in a so-called "air bath"; e.g., a heating mantle with an inserted "ceramic spider" is suitable.
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