Why warm drinks taste more alcoholic than cold ones

Beer is most refreshing when it is ice-cold, while spirits like whisky taste most alcoholic at warmer temperatures – and those shifts in flavour may be due to the way water and ethanol molecules cluster together within a beverage.

Lei Jiang at the Chinese Academy of Sciences and his colleagues wanted to study how factors like temperature and alcohol by volume (ABV) affect molecular behaviour in drinks like beer, rice wine and the whisky-like Chinese spirit baijiu – and what that may mean for their taste.

They first measured the surface tension of these alcoholic beverages while increasing the drinks’ ABV levels. Then they used nuclear magnetic resonance imaging and computer simulations to “zoom in” on combinations, or clusters, of water and ethanol molecules in beverages at different ABVs and temperatures. Finally, they conducted taste tests in partnership with Chinese baijiu company Wuliangye.

Jiang says that what they found surprised them, defying what chemists once thought was “common sense”. While he and his colleagues expected surface tension to evenly decrease as the ABV of a drink increased, it actually changed in discrete “steps”.

The researchers uncovered that these jumps happened when clusters of water and ethanol molecules changed shape, shifting from compact, pyramid-like structures to long, chain-like ones. Jiang says that colder and less alcoholic liquids had a greater proportion of pyramid clusters and were associated with a more refreshing flavour.

“When the temperature drops, the structure becomes more compact, which is why chilled beer has a more stimulating taste,” he says.

In warmer drinks and those with higher ABVs, more chain-like clusters dominated, and their flavour was more pungent and ethanol-heavy.

Gavin Sacks at Cornell University in New York says the study found novel details about the chemistry of ethanol and water in beverages, but that connecting molecular clusters to taste is very complicated. The burning flavour of ethanol stimulates the same taste receptors that sense heat. As a result, it is difficult to isolate which chemical property of a warm drink – the way its molecules cluster, its temperature and how it interacts with other liquids in the human mouth – is responsible for changes in its taste, he says.