Bad Kissingen Brewer’s Day Aroma impressions of different hop varieties

This was the conclusion drawn by Dipl.-Ing. Ralf Mezger, Scientific Assistant at the Faculty of Technology I in the Weihenstephan Scientific Centre for Nutrition, Land Use and Environment of the Technical University of Munich, in his lecture on the occasion of the 7th Bad Kissingen Brewer’s Day 2004 held in Bayreuth on March 25th, 2004. 99.5% of hops produced worldwide is processed in breweries, the remainder goes to the pharmaceutical industry. Valuable components of hops are:
--hop resins: 10 - 25% of hop dry matter;
--hop oils: 0.5 - 3.0% of hop dry matter;
--hop tannins: 4 - 14% of hop dry matter.
75% of hop essential oils are terpene hydrocarbons and 25% oxy-compounds. They also contain small quantities of sulphur compounds. Threshold levels are 5 µg/l and > 20 µg/l..

The amount and composition of hop oils varies depending on variety, growing conditions, climate, maturity and hop treatment.
Mezger referred to the following hop aroma active substances in beer: linalool, humulene II, humulene epoxide II, humuladienone, hop ether, karahanaether. These go together under the term "total hop oils". (R-)-linalool and (S)-linalool produce a definite hop flavour in beer. The table lists the aroma flavour impression of various hop varieties. According to Mezger, flowery, fruity and citrus-like are the main aroma impressions imparted by hops.
lTechnological possibilities and hop aroma
A number of technological measures are available for influencing hop aroma:
-Point at which hops is added: bitter hops at the beginning of boiling/aroma hops towards the end of boiling or in the whirlpool (forced aged beers are getting somewhat more popular);
-Whirlpool: hop addition to the whirlpool at temperatures below 90°C, tests at 60°C yielded best results;
-Composition of brewing liquor;
-Biological acidification.
The effect of aroma hop addition at the start of boiling versus towards mid-time of boiling still remains to be determined.
lSpecial effect of hops
Xanthohumol (prenylflavonoid) is particularly effective in hops. It has
--a cancer-inhibiting effect (in vitro);
--an antioxidative effect;
--concentration in beer: <1mg/l;
--can be used in other beverages or in the pharmaceutical industry.
Xanthohumol is found in the lupuline glands of hops and is isomerised during wort boiling. Hops also acts as a preservative.
Hop polyphenols inhibit growth of various micro-organisms. Hop bitter substances as well as alpha and iso-alpha acids and hulupones improve foam stability and adhesion.
Hops has more to offer than just bitterness values - it has a positive influence on beer taste and head retention, its acts as a preservative and contains valuable xanthohumol.