Determination of bitter iso- alpha-acids and alpha- and beta-hop acids in beer
It is important to quantify α - and β -hop acids (humulons and lupulons) as well as bitter iso- α -acids (isohumulons) on the all stages of beer production. Hop acids are the biochemical markers of a certain hop type. Bitter iso- α -acids stabilize the beer foam, suppress the growth of undesir able microorganisms and give the beer its bitter taste.
The method has two stages – sample preparation and analysis. The first stage is based on the sample degassing, extraction of acids into isooctane, evapora tion and subsequent dissolving of the residual into water / methanol mixture. Analysis is based on the differential migration of ionic forms of the analysed compounds in the fused silica capillaries under the influence of the applied electric field. Sodium dodecyl sulphate is added to the electrolyte to provide the so-called pseudostationary phase which leads to a better resolution. Detection is done at 215 nm. To increase selectivity it is possible to switch the wavelength to 315 nm during the run.
Determination of the total hop and bitter acids concentration is done by normalization for the each acid group. In general, the measurement range for bitter acids is 5–200 mg/L , for hop acids 1–100 mg/L.