“Two years ago, Xiaotao Yang and I were drinking beer together. He had just finished his doctorate degree thesis and asked me, ‘what should we do next?’” says Lei Jiang, lead author of a new study published in the materials science journal Matter.

Yang and Jiang are material scientists at the Chinese Academy of Sciences.

“At the time, I was a scientific committee member of one of the biggest Chinese alcoholic beverage companies, and I had the idea to ask the question ‘why does Chinese baijiu have a very particular concentration of alcohol, either 38%–42%, 52%–53%, or 68%–75%?’”

Baijiu is a clear grain liquor from East Asia. It’s typically distilled from fermented sorghum (a type of grass), though it is also sometimes made from rice, wheat, barley or millet.

“Then we decided, let’s try something, so I put a drop of beer on my hand to see the contact angle,” says Jiang.

Contact angle is a measure of surface tension. For example, water has a low contact angle which is why it appears bead-like when placed on a surface. Solutions with high alcohol concentration, however, have a higher contact angle meaning they flatten and spread out.

Contact angle also reveals how molecules within the droplet interact with each other and the surface below.

After plotting the concentration of ethanol (alcohol) against contact angle, the scientists were surprised with what they found. There is no linear relationship between alcohol concentration and contact angle.

Instead, increasing the amount of alcohol leads to a series of plateaus and sharp rises in the plot. Further experiments showed that this arises out of the formation of clusters of ethanol and water in the solutions.

At low concentrations, ethanol forms pyramid-like structures around the water molecules. At high concentrations, the ethanol molecules arrange end-to-end in a chain.

They also found that these structures change depending on temperature.

For example, 38%–42% and 52%–53% ethanol solutions have distinct cluster structures at around room temperature, but this difference disappears at higher temperatures, like 40°C.

“Although there is only 1% difference, the taste of baijiu at 51% and 52% is noticeably different; the taste of baijiu at 51% is similar to that of lower alcohol content, such as 38%–42%. So, in order to achieve the same taste at a lower alcohol content, the distribution of baijiu products ranges most within the 38%–42% and 52%–53% categories,” says Jiang.

The researchers also found that there is an increase in ethanol chains at 5°C in 5% and 11% ethanol solutions – the concentration range of beer – giving it a more “ethanol-like” taste which is generally preferred.

“At low temperature, the tetrahedral (pyramid-shaped) clusters become the low concentration amount, and this is why we drink cold beer,” says Jiang.

The researchers say their research could help beverage companies produce the best flavour with the lowest alcohol concentration.

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