Production of an iso- alpha -acid preparation from hops

摘要

A method of providing a high quality iso- alpha -acid preparation is described. The method involves extracting a high quality primary extract containing alpha -acids from hops using liquid CO2 and isomerizing the alpha -acids in the primary extract. The liquid CO2 extraction is performed at a sub-critical temperature of not less than -5 DEG C. The primary extract contains alpha -acids, beta -acids, hop oil and usually no significant amounts of other organic compounds originating from the hops. In the preferred method the primary extract is not purified and the isomerization is performed by boiling an alkaline solution of the extract. This boiling can be utilized to remove the hop oil. The beta -acids can be readily removed by acidifying the solution of iso- alpha -acid and filtering off the precipitated beta -acids. The iso- alpha -acid preparation is of outstanding purity and can be added to beer after fermentation and in particular to bright beer after final filtration to provide bitterness.