The Contribution of Post-Fermentation Bittering to Beer Composition and Stability

By Robert T. Forster II, Hugo Patino and J. Colin Slaughter lCoors Brewing Company, Golden Colorado *lCBD, Heriot-Watt University, Edinburgh, Scotland, UK. This poster was originally presented at the MBAA 112th Anniversary Convention, Keystone, Colorado, 1999.

Abstract
Use of commercial and lab-prepared pre-isomerized hop extracts, yielding hopped beers from 10.8 to 37.6 IBU levels, resulted in improved microbiological and foam stabilities compared to unhopped beers. The hopped beers also had significantly lower concentrations of Zn, Fe, and Cu than the unhopped beers. Poorer physical and flavor stabilities were observed in some of the post-fermentation hopped beers resulting from higher total polyphe- nols, which included the iso-alpha acids themselves, and higher unsaturated fatty acids present in the pre-isomerized hop extracts, respectively. The results indicate that use of pre-isomerized hop extract in beer in a post-fermentation manner is likely to be entirely beneficial with regard to bittering, foam, and microbiological stabili- ties. However, from a flavor stability standpoint, care must be taken to avoid coincidental addition of saturated and unsaturated fatty acids from the pre-isomerized hop extract when post-fermentation bittering is practiced.
Keywords: Post-Fermentation Hopped Beer, Microbiological Stability of Post-Hopped Beer, Hop Extract/Microbiological Stability, Hop/Extract/Foam Stability, Hop Extract/Physical Stability  

Sintesis
El uso de extractos de lupulo comercial o que ha sido isomesizado en un laboratorio que produce cervezas con lupulo con niveles de 10.8 a 37.6 IBU, ha resultado en mejores estabilidades de espuma y micro biologicas que en cervezas sin lupulo. Las cervezas con lupulo tambien tienen concentraciones rn3s bajas de Zn, Fe, Cu que las cervezas sin lupulo. En algunas de las cervezas con lupulo despues de la fermentation se observaron estabilidades de sabor y fisicas mas pobres debido a la mayor cantidad de polifenoles, los que incluyen a los mismos acidos isoalfa y a la mayor cantidad de acidos grasos no saturados presentes en los extractos con lupulo que han sido isomerizados. Los resulta- dos indican que el uso del extracto de lupulo que ha sido isomeriza- do en la cerveza despues del proceso de fermentation es probable que sea enteramente benefice con respecto a las estabilidades de espuma, amargura y micro biologicas. Sin embargo desde el punto de vista de estabilidad del sabor, se debe tener cuidado en evitar la adicion coincidente de acidos grasos saturados y no saturados del extracto con lupulo que ha sido isomerizado cuando se practica el metodo de amargura despues de la fermentation.