In the past year or so, there has been lots of discussion and work around thiols and brewing, and some of it is pretty complicated stuff for anyone who is not a microbiologist. I hope this short explanation will answer some questions but I would certainly direct you to the Escarpment Labs blog, amongst others, for more information.
I first learned about thiols and the gene associated with freeing them through a podcast by the Master Brewers Association released last October. In it, there was a complex but understandable conversation about "thiolized" CRISPR modified yeast and the process of bringing out additional aromas that are locked up in both malt and hops.
Curious to find out if the product discussed in that podcast, Cosmic Punch from Omega Yeast Labs, was coming to Canada, I reached out to Omega and quickly got a reply from Lance Shaner, one of the founders of Omega, who shared with me that the "paperwork was in the works" to allow them to export it to Canada. Not long after that, I heard the first hints that our very own, equally famous yeast manufacturer, Escarpment Yeast Labs of Guelph, was hard at work on a version of their own. This yeast has now been released under the name Thiol Libre and is readily available for both pro and homebrewers.
So, back to the topic of thiols. Thiols are a family of organic compounds that contain sulphur, meaning they can have a very distinctive odor, and one that can be detected at very low concentrations. This makes some thiols ideal for adding a distinct smell to a dangerous odorless product like natural gas, making it easy way to warn us of its presence. Thiols are also the compound that gives skunks their defensive odor, so clearly different thiols exhibit different aromas and the ones we are after exhibit tropical fruit aromas. There are both free and bound (locked) thiols and as the name suggests, some are volatile and need no coaxing to release them, and others are locked up or bound. This is technically know as a precursor thiol. As a result, it has long been the practice to use hops high is free thiols to add the flavours and aromas found in big juicy NEIPA beers, for example, but the downside is that those hops tend to be some of the most expensive on the market.
To add another facet to the whole process, it has recently been discovered that some very lightly kilned base malt and some lower cost hops contain precursor thiols that can add similar aromas, however what is needed is a way to unlock those thiols and this is where the magic happens!
Backing up one step, I need to add here that precursor thiols in hops need to be converted from one form to another before the magic yeast can free them, and this is done in the mash. By adding hops high in precursor thiols to the mash (such as Cascade, Saaz, Calypso, and Perle), the enzymes that are already at work on the barley starches will convert the Type A thiol into a Type B thiol (not their real names!) and the yeast can then release the aroma from them during fermentation. This applies to precursor thiols in both the malt and hops. These same hops may already contain a quantity of Type B (free) thiols that the yeast will release when they are added during whirlpool or dry hopping, but adding hops to the mash results in more Type B thiols available for release. Simple but brilliant, mash hopping is once again a thing!
Both Escarpment Labs and Omega have been able to create a strain of yeast that can biotransform those tasteless odorless precursor thiols and release them to be detected as aroma compounds through normal fermentation. This is done by enhancing the activity of a gene in the yeast named IRC7*, which is mostly inactive in other beer brewing yeasts. However, it should be pointed out that switching from high free-thiol hops (Citra and Galaxy) in favour of lower cost hops with quantities of precursor thiols and using Thiol Libre yeast will not replicate the results of the Citra/Galaxy NEIPA. This is not a shortcut to cost savings with the same result, but using Cascade in the mash and whirlpool and fermenting with Thiol Libre will result in more tropical fruit aroma than the same brew with a non-thiol enhancing yeast.
I hope this sheds some light and adds to your understanding of how to use this new yeast as another tool in your brewing kit. For me, it further underscores two really key facts; we are incredibly lucky to have such an ingenious and highly motivated manufacturer right here in Ontario who spends as much time and energy as they do perfecting our brewing experience. Big thank you to Escarpment Labs! Secondly, I am always amazed at how complex this "simple" process of making beer really is. With highly modified malts, state of the art brewing systems, access to hops from 4 different continents of the world and fresh, cutting edge products from our yeast suppliers, this really is a great time to be a homebrewer!
*It should be noted that this strain of yeast does not contain genetic material from another organism, rather, the existing genetic material has been enhanced to amp up the activity of the gene responsible for the biotransformation of the precursor thiols. This is very different from a product in which foreign DNA has been spliced in to introduce or enhance the functionality of a gene. In the words of Richard Preiss or Escarpment Labs:
"Methods used to develop new yeasts for enhanced thiol biotransformation includes genetically engineering existing strains to have higher IRC7 activity, or breeding strains with naturally high IRC7 activity to achieve “hybrid vigor”."