BY MARIA BURKE | 8 NOVEMBER 2023
Many farmers are facing a challenging future as climate change reshapes the agricultural landscape. Now, a new study has found that rising temperatures and more droughts are driving down the yield of European hops, which give beer its distinctive taste and aroma.
The demand for aromatic hops with high bitter acid content has boomed as the craft beer industry has taken off. But the cultivation of high-quality aroma hops – the flowers of the hop plant – is restricted to relatively small regions with suitable conditions. Now researchers have concluded that climate change will make it necessary to expand growing areas by a fifth.
The team from the Czech Academy of Sciences collected data between 1971–2018 from Germany, Czechia, and Slovenia (Nature Communications, doi: 10.1038/s41467-022-33729-4). They found that after 1994, hops started to ripen 20 days earlier and production declined by almost 0.2t/ ha/year. Modelling predicted a 4–18% reduction in yield by 2050, depending on the region, and a 20–31% reduction in hops acids, with the largest declines expected in southern regions.
The researchers note that farmers have already responded to climate changes by relocating hops to valleys with more water, building irrigation systems, changing how crops are orientated and spaced, and breeding more resistant varieties.
Weather conditions before and during development of the hop flower influence final quality, explains Glen Patrick Fox of the University of California, Davis, US, who was not involved in the research.
‘Excess heat and/or drought can reduce flower development. Alpha-acids are produced from complex metabolic pathways, which operate in an ideal temperature range. Significantly higher temperatures impact these metabolic pathways and the final profile of all the beer-related compounds of interest, including the acids, as well as the oils which bring the aroma,’ he said.
This is common in all crops. Fruit trees produce less fruit and their fruit tastes different if conditions during ripening change the metabolic pathways responsible for fruit production, taste and aroma, Fox explains. ‘Under extreme stress, plants will allocate resources to ensure survival, which sometimes means a shift of metabolic pathways making more of the compounds which are more important for survival. For hops, this could come at a cost of the alpha-acids and aroma compounds brewers are interested in.’
Coffee beans are particularly susceptible to high temperatures, causing beans to ripen too quickly. Climate change looks set to reshape coffee-growing regions with potentially large socio-economic effects. Researchers from the Zurich University of Applied Scientists, Switzerland, predicted in 2022 that key growing regions in Brazil, Indonesia, Vietnam and Colombia would decrease by around half by 2050; these countries produce most of the world’s dominant variety, Arabica (Plos One, doi: 10.1371/journal.pone.0261976). In one scenario, Brazil would see a reduction of 76% in suitable growing areas and Colombia 63%; while regions including Argentina, South Africa, China and New Zealand may become more suitable.
The study also looked at cashews and avocados, predicting mixed fortunes. For cashews, rising temperatures would boost highly suitable growing areas by about 17% globally by 2050, but certain countries, particularly in Central and South America, and West Africa, would be badly hit. In one scenario, Benin would lose half its suitable areas.
For avocados, highly suitable areas would decrease globally by 14% due to drier or wetter conditions, depending on the region. Peru would lose around half its suitable areas, while Mexico – the world’s largest producer of avocados – would see a major increase in suitable lands, up over 80%. Positive impacts are due largely to rising minimum temperatures and increased rainfall.
The researchers say climate change adaptation will be necessary in most major producing regions of all three crops. Measures include relocating production to higher altitudes and latitudes, breeding more resistant varieties and, for coffee, replacing Arabica with its tougher relative Robusta in certain regions. Robusta requires a mean annual temperature of around 23°C compared with Arabica’s 19°C, but it tends be used in instant coffee because of poorer flavour.
Research into different coffee strains is ongoing. Back in 2021, an international team of researchers reported that a ‘rediscovered’ coffee species could tolerate temperatures of almost 25°C while also boasting a complex superior flavour (Frontiers in Plant Science, doi:10.3389/fpls.2020.00616). Stenophylla, a rare wild species from West Africa, also has the potential to be used in breeding to produce new, climate-resilient coffee crops for global consumption. Stenophylla had not been seen in the wild since 1954 but the team discovered a healthy crop in Sierra Leone.
‘Future-proofing the coffee supply chain to deal with climate change is vital,’ said Aaron Davis, Head of Coffee Research at RBG Kew, and lead author of the paper. ‘To find a coffee species that flourishes at higher temperatures and has an excellent flavour is a once-in-a-lifetime scientific discovery – this species could be essential for the future of high-quality coffee.’