Thiolized Beer
What are thiolized IPAs? Well for starters, they’re delicious. For a more detailed answer, you need to know what thiols are, so grab a beer and settle in for a bit of a chemistry lesson.
Image Credit: Scott Janish
Most of the flavor that hops contribute to beer comes from the small yellow lupulin glands inside a hop cone. There are three major classes of chemical components within the lupulin: α-acids, β-acids, and essential oils. The first two contribute to the bitterness of the beer, while the third is responsible for the aromatics. The essential oils can be broken down into hydrocarbons which contribute spicy/herbal/green flavors, oxygen-containing compounds such as the terpene alcohols that produce the floral/fruity/citrus flavors popular in American hops, and a tiny percentage of sulfur-containing compounds. This last group can further be subdivided into thiols, sulphides and thiosters. While the last two have undesirable aromas, the thiols have a huge aroma impact on beer, lending the tropical grapefruit/passionfruit/guava characteristics that have made NZ hops popular. It's no surprise that thiols haven't been studied in depth until recently; hop oils are only 1-4% of the total mass of a hop cone, and the sulfur-containing compounds less than a percent of that, with the positive species of thiols an even smaller portion. At these minuscule concentrations, there are only a few labs in the world capable of analyzing thiols in hops and beer, but because of their low sensory threshold they have a big impact.
To summarize: thiols exist in very small amounts in hops, and certain types of thiols are responsible for the tropical fruit flavors in hops and therefore beer.
Image Credit: Omega Yeast
It turns out that while the amount of thiols in hops is small, there are a huge number of "thiol precursors"--thiols bound to a larger amino acid chain--that are not flavor or aroma active. If we were able to cleave those bonds, the amount of thiols that could be released into the beer would be hundreds of times larger than the highest thiol hops like Nelson Sauvin. Well as it turns out, yeast is actually capable of doing just that. This behavior is exhibited in some wine yeasts--think of a fruity New Zealand Sauvignon Blanc--but the gene is dormant in most ale strains. Researchers have recently discovered how to reactivate the gene responsible for producing the β-lyase enzyme that breaks these bonds, unlocking this ability for brewers as well.
So a "thiolized yeast" is a yeast that has been modified to release bound thiols found in the wort (either via the β-lyase pathway or another), and a "thiolized IPA" is an IPA that takes advantage of a thiolized yeast to maximize the tropical fruit character in the beer.
When we go to build that thiolized IPA recipe, there are few things we can do to either temper or boost the thiol character. The first one is to control the amount of thiol precursors that the yeast has to work with during fermentation. While we’ve mostly talked about thiols in relation to hops so far, barley can actually be a great source of precursors as well. Early research indicates that lightly kilned malts provide more thiol precursors, so we use flaked barley (unkilned) to boost the amount of precursors in the wort.
The other big thing we have to be aware of when building a thiolized beer is how much hops to use and when. While hops contain thiol precursors, they paradoxically appear to reduce the amount of free thiols in the beer when used late in the process. In building the recipe, we must balance the flavors a big dry hop provides against the prominence of the thiol character we’re looking for. Finding that balance can unlock a beautiful aroma where the passionfruit of the thiols compliments the bouquet of the hops.
Most of the early thiolized beers that are just hitting the market have been hazy IPAs, but there is a lot of territory out there remaining to explore. In particular, we’re excited about using these yeasts to bring the bright tropical fruit character to more of a west coast style IPA. Keep an eye on our social media for new beer announcements as we explore the future of IPA!