General Considerations

  • The nitrogenous constituents of wort include amino acids, peptides, polypeptides, proteins, nucleic acids and their degradation products.
  • Some of these nitrogenous constituents are essential factors for yeast growth during fermentation and wort must contain an adequate supply.
  • Most proteins are not assimilated during fermentation although some may be precipitated and adhere to the yeast. Excessive levels of proteins in beer can lead to fining problems.

Range of Values

  • Levels of total soluble nitrogen constituents should be in the ranges 600 – 900 mg per litre (at 1040°) for wort containing adjunct and 750 – 1000 mg per litre for an all-malt wort. Values are measured in the brewery and calculated to 1040° (see Appendix 3).
  • For free amino nitrogen, the target is 160 – 190mg per litre (measured in the brewery and calculated to 1040°). At levels below 160mg per litre there may be problems with sticking fermentations. Beers with high levels of free amino nitrogen constituents are prone to infection by micro-organisms.

Operational Protocols

  • Protein is coagulated in wort boiling, the amount coagulated depends on the pH and the duration and vigour of the boil

Measurement Protocols

  • The protein content of wort is measured at existing gravity (Institute of Brewing Recommended Method 2·9) using the Kjeldahl method and the value adjusted to 1040° (see Appendix 3).
  • Free amino nitrogen is measured by the Institute of Brewing Recommended Method 8·3.