Regression analysis of some beer volatiles.

Haukeli, A.D., Jacobsen, T. and Lie, S.

Abstract
All malt beer, 91 samples, from 18 Norwegian breweries were analysed on a Varian Aerograph 204 gas chromatograph with flame ionization detector. Acetaldehyde, ethyl acetate, ethanol, n propanol, isobutanol, isoamylacetate, amyl alcohol, diacetyl and 2,3 pentanedion were determined in decarbonated beer samples; 50 ml samples in 100 ml flasks were treated with 1 ml n butanol as internal standard and equilibrated by magnetic stirring at 35 degrees C for 30 min. The silicone rubber stoppers coated with Al foil were punctured to maintain normal pressure and 2 ml vapour samples were drawn for analysis in a syringe heated to 40 degrees C. From the results the regression equations and standard errors of estimate were calculated to show high correlation between the esters and the corresponding alcohols, viz. ethyl acetate and ethanol; isoamyl acetate and amyl alcohol. There was also close correlation between ethyl acetate and acetaldehyde, isoamyl acetate and ethyl acetate, amyl alcohol and isobutanol, ethanol and acetaldehyde, ethanol and n propanol, ethanol and amyl acetate and between diacetyl and 2,3 pentanedione. These correlations all had a significance higher than 99.9%. The variation in the production of isobutanol was much greater among the different yeast strains than from one brewery to another when the same yeast was used. 2 Acetolactic acid is the precursor of diacetyl and of isobutanol but diacetyl is removed during maturation and the correlation between isobutanol and diacetyl was not significant. The nature of the yeast may affect the formation of volatile products but wort composition and fermentation temperatures influence the final level of by-products.
Keywords: alcohol analysis beer gas chromatography ester statistics volatile compound