What Malt Can Do for Your Thiols

It’s long been known that malt contains precursor compounds that can be unlocked via fermentation for bright, tropical-fruit aromas. Researchers are beginning to quantify those contributions, and brewers are putting them to work in the brewhouse.

IN THE PURSUIT OF POPULAR tropical aromas, it’s become fashionable to harness thiols and figure out how to maximize their contribution from hops. Ironically, that attention to thiol expression has yet to focus much on the ingredient that’s most responsible for it: malted barley.

Research is ongoing in all areas, but so far, hops and genetically modified “thiolized” yeasts are the tools that brewers are employing most often in the thiol workshop. However, a few scientists and brewers are discovering just how powerful a lever malt can be in this realm.

“Pretty much all of the thiols coming out of beers are from the barley,” says Laura Burns, director of research and development at Omega Yeast. “If there’s a recipe that has hops and [one that] doesn’t have hops, the difference in thiol output is about 10 percent.”

Indeed, brewing science has suspected this for years, even if the knowledge hasn’t trickled out broadly. In 2008, Japanese researcher Toru Kishimoto and his team found that 3-mercaptohexanol (3MH), a volatile thiol responsible for grapefruit, rhubarb, and passion-fruit aromas, occurred in unhopped beers-a strong suggestion that such a compound was malt-derived. In 2016, French researcher Laurent Dagan and his fellow researchers at Nyseos for the first time identified and quantified the cysteinylated (Cys-) and glutathionylated (Glut-) precursors of 3MH (odorless) in several types of barley, rice, sorghum, and wheat malts. They further concluded that the specific malt variety, the malt’s roasting level, and probably enzymatic activities all contributed to the variation of thiol potential in the wort- and thus, potentially, the free thiols in beer.

As brewers work toward a more nuanced, integrated approach to unlocking and incorporating the bound thiols naturally present in their raw materials, their malt selection and mashing process are critical. However, Dagan emphasizes, the practical applications of this knowledge are so far still in development. It’s too soon to conclude that certain malts always contribute particular precursors or that adjusting a mash in a certain way will have a guaranteed result in terms of thiols in beer. Fermentation is a key point for thiol release and, thus, for the aromatic contribution of free thiols.