Solventless process to assess thiols in beers

Researchers have developed a way of measuring the compounds in beer that give it distinct hoppy and fruity aromas. The innovation will provide brewers with greater control in the production process, allowing them to differentiate among subtle flavours.

Hoppy beers such as pale ales are becoming increasingly popular. One reason for this is their pleasant, fruity aroma that partially stems from compounds called thiols.

Brewers have been looking for an accurate way to track thiols in beer, but current methods are typically not sensitive enough or require the use of potentially harmful substances.

Now researchers present an automated, solventless process to assess thiols at very low concentrations, publishing their findings in the American Chemical Society’s Journal of Agricultural and Food Chemistry.

Thiols, along with other compounds such as terpenes and esters, contribute to the enjoyable odours in ‘hop-forward’ beer styles. Although minimal amounts of thiols are present in beer, a little bit of these compounds goes a long way toward achieving a hoppy flavour and fruity aroma.

Brewers would like more information about these volatile substances, but it’s challenging to detect such small quantities accurately. Previous studies have reported complex, multistep methods for thiol analysis in beer. However, the approaches could not measure all of the thiols brewers want to know about, and some processes used harmful, mercury-containing compounds.

Thiols also contribute to wine aromas, and researchers have used coated polymers that they can put into the air above the beverage to convert aerosolised wine thiols to more easily measurable compounds. The downside is that this method is not sensitive enough to measure the trace concentrations in beer. Nils Rettberg and colleagues wanted to modify previous methods and come up with a safer, faster and more sensitive approach to develop a more robust analysis.

In initial experiments to develop the new process, the team modified the sample preparation method used in wine analyses to convert aerosolised thiols to compounds with higher analytical sensitivity. Then, they tweaked and applied a tandem mass spectrometry approach to detect and measure the resulting compounds maximally. Finally, the team tested their new method on 13 commercially available beers from multiple countries made with hop varieties expected to have high thiol content. The distribution of thiols within the selected beers was consistent with prior studies.

Surprisingly, the team could only detect one of the three expected thiols in a beer with real grapefruit added, suggesting that the fruit itself likely contributed scent compounds other than thiols.

The researchers said the method meets the requirements to detect thiols in beer, while also processing samples in a safer, simpler and quicker manner.

Image credit: ©stock.adobe.com/au/Grecaud Paul