The influence of temperature and sunshine on the alpha-acid content of hops

Abstract Analysis of trials carried out by the European Brewery Convention during 1968–1972 in 6 countries on 4 varieties of hop (Fuggle, Northern Brewer, Hallertau and Saaz) shows that the mean temperature and mean duration of sunshine between the date of coming into hop and the date of picking are the critical meteorological factors affecting the alpha-acid content. There is an optimum temperature for each variety lying between 16° and 17°C; below this optimum quality decreases rapidly with temperature, but above the optimum there is a slower decrease in quality with increasing temperature and some indication that increasing sunshine is the more significant factor.