An investigation into the changes in composition of hop cones in the final stages of ripening and their effects on the brewing properties of the harvested hops is described. In 1990, 1991 and 1992, samples of four hop varieties (Willamette, Mount Hood, Nugget and Galena) were harvested at weekly intervals over a six week period (from four weeks before to two weeks after the normal harvesting date for the variety concerned) at a farm in Washington State, USA, and analysed for dry matter, moisture, bitter substances and essential oils. A portion of each sample was dried and stored for six months before being analysed to determine the stability of its alpha acid content. The dry matter content increased as the hops ripened, so that a later harvest would increase the apparent yield (dry weight of cones harvested per unit of land area), but while the alpha acid content reached a maximum when the dry matter content was between 22 and 24%, the beta acid content peaked at a dry matter content of less than 22%, while the total essential oil content increased steadily throughout the trial period in each year, as did the quantity of myrcene relative to other essential oil constituents (though the ratio of humulene to caryophyllene remained stable), the quantity of cohumulone relative to the other alpha acid fractions and the quantity of colupulone relative to the other beta acid fractions. While the storage stability of the alpha acid content of the bittering varieties (Galena and Nugget) was not significantly affected by the harvest date, that of the aroma varieties (Willamette and Mount Hood) was improved by late harvesting. These findings show that it is possible to obtain hops with brewing properties somewhat different from those which are normally characteristic of the variety in question by harvesting earlier or later than usual.
Keywords : composition harvesting hops properties quality ripening time