European hop varieties are prized and used by brewers around the world, but rising temperatures and less rain are reducing yields and the concentration of compounds that give beer its refreshing acidity. Researchers observed this trend by analyzing data from five locations in the Czech Republic, Germany and Slovakia, which, along with Poland, are the main hop growers in Europe, said study co-author Miroslav Trnka. Yields fell between 9.5 and 19.4 percent in four locations and were stable in a fifth when data from 1995-2018 was compared with 1971-1994. Meanwhile, the concentration of bitter compounds, alpha acids, decreased. Extrapolating from the data, the researchers predicted a four to 18 percent decline in yield compared to 1989-2019, while alpha acid concentrations could drop by 20 to 31 percent as temperatures and precipitation are affected.