Sweet water and bubbly beer

The sweeter side of heavy water

In deuterium oxide, or heavy water, deuterium atoms, which have a proton and a neutron, replace water’s hydrogen atoms, which have only a proton each. This subtle atomic swap produces a strange difference between the water from your tap and pure heavy water: D₂O tastes sweet. Masha Niv, a professor at the Institute of Biochemistry, Food Science, and Nutrition at the Hebrew University of Jerusalem, learned of this gustatory curiosity in a discussion with Pavel Jungwirth, a professor at the Czech Academy of Sciences’ Institute of Organic Chemistry and Biochemistry. Their labs collaborated to understand why heavy water tastes sweet (Commun. Biol. 2021, DOI: 10.1038/s42003-021-01964-y).

Taste tests confirmed the sweet taste of heavy water: participants rated the D₂O samples between three and four on a scale of one to nine, Niv tells Newscripts. The researchers also found that adding sugar or the artificial sweetener cyclamate to D₂O enhanced the solution’s sweetness for the human sensory panel.

Only subatomic particles distinguish deuterium from hydrogen. But neither water nor heavy water is similar to the complex sugars that typically trigger sweetness. Niv wondered if TAS1R2/TAS1R3—taste receptors on the tongue and palate that participate in perceiving sweetness—were involved. Cell-based assays and sensory experiments confirmed they were, and molecular dynamics simulations by Jungwirth’s team revealed that the receptors became more rigid when immersed in heavy water than in regular water. The researchers are investigating what the receptor rigidity might mean.

Understanding that D₂O interacts with the TAS1R2/TAS1R3 receptors raised even more questions for Niv’s team. The TAS1R receptor family is also responsible for the umami taste of monosodium glutamate (MSG), but adding MSG to heavy water did not change MSG’s savory taste compared with MSG in H2O. The researchers also tested bitterness by adding quinine to heavy water. Although bitterness is not modulated in the same way as sweetness, D₂O did reduce the bitter taste of most of the quinine samples.

The researchers are still studying what makes heavy water sweet, and they are exploring the mechanism of its interaction with the TAS1R2/TAS1R3 receptors as well as its interactions with other sweet receptors. But if you’re looking for a sweetener, stay away from D₂O; heavy water is toxic at high doses because it can slow metabolism and cause cell damage. This Newscriptster suggests good old sugar instead.

Better beer bubbles

Gérard Liger-Belair, a professor of chemical physics at the University of Reims Champagne-Ardenne, has spent much of his career exploring the bubbles produced in champagne and other sparkling beverages. Now, Liger-Belair and colleague Clara Cilindre have turned their attention to beer (ACS Omega 2021, DOI: 10.1021/acsomega.1c00256).

Bubbles that arise from poured beer come from tiny imperfections in the beer glass. These imperfections must be a certain size, with larger ones producing more bubbles than smaller ones. Glass manufacturers can engineer these bubble-making imperfections into beer glasses. The researchers also determined a critical concentration of dissolved carbon dioxide that’s needed for bubbles to form. Temperature was another key factor: lower temperatures lead to fewer, smaller bubbles that are released more slowly and over a longer period.

Liger-Belair tells Newscripts that beer bubbles, which form foam, can influence not only the visual appearance of the beer but also the drinker’s experience, “as bubbles also impact the transfer of CO₂ and aromas from the liquid phase to the headspace of the glass.”

Paul Hughes, a professor of brewing and distilling at Oregon State University, contends that the volume of bubbles is another important factor. The larger the bubbles, Hughes says, the better the foam. “My take is that for reliable foam formation and stabilities, homogeneous bubble size and consistent glass surfaces are the key,” Hughes tells Newscripts.

Liger-Belair says, “We can easily imagine modifying some beer and glass parameters for a better overall sensory experience.” Brewscripts, um, Newscripts looks forward to a better pour.

Please send comments and suggestions to newscripts@acs.org.