Thiol Precursors - Creating fruity hop flavors without hops!


By Nick Mclawhorn, Nordeast Brewers Alliance

Big fruit flavors from hops are extremely popular - but what if you could intensify that fruit forwardness without large doses of hops with vegetal matter, bitterness, or adding extra gravity points from fruit?
One way to approach this is a combination of using yeast strains that are predisposed to the biotransformation process of breaking thiol bonds created from your brewing ingredients.
While we have seen a lot of information emerging on mash hopping and thiolized yeast strains, to the surprise of many, it’s actually the grains that possess the largest amount of bound thiol precursors needed for the biotransformation process that can create intense fruit flavors popular with today’s IPAs and Pale Ales.
Thiols are compounds that present intense aromas of guava, passion fruit, grapefruit. In true homebrewer spirit, when I first saw these strains at the homebrewer level, I grabbed a pouch and proceeded to brew an American Pale. The results lead to me looking even further into just how the yeast produce these flavors. I found some great information from Berkeley Yeast and Omega Yeast Labs.
Much of the 3MH and 3MHA compounds in brewing ingredients are bound Cys-3MH - meaning they are nearly odorless/tasteless when derived from more traditional brewing ingredients and processes. However, some yeast strains contain a gene(s) that produces an enzyme that breaks these bonds.
  • IRC7 encodes the enzyme ß-lyase
  • CSL expresses AAT enzyme
The key then is understanding that it is this biotransformation breaks the bond to release large quantities of 3MH/3MHA thiol compounds (guava and passionfruit), and that I should be on the lookout for ingredients that have an abundance of these bound thiols - so hops, right? Well it was the two below graphs and an email exchange with Lance from Omega yeast that shifted my focus to malt selection for those big fruity notes:

Mash Hopping and Thiols

Thiols from Malt Precursors

With this new information, and the recent release of Omega’s Lunar Crush, I enlisted the help of my homebrew club, Nordeast Brewer’s Alliance, and we conducted an education topic to compare some ingredient and process variables, then have our club members sample and give feedback during a monthly meeting.
Why would this be something to take into consideration for your recipe? The added complexity offered from these ingredients is one of the main reasons. If you have felt that your beers are one dimensional (especially hop-forward IPAs, Pale Ales, and Italian Pilsners) this is a great way to create more layers of flavors or add complexity by complementing those expensive hops.
As you can also see below, this is supported by anecdotal feedback from tasters, and we were able to have the beers tested with an e-tongue that supported our perceptions. I have listed the condensed tasting notes for the variants as well.

The Hop Variants

SG 1.050 with Eraclea Malt, Lunar Crush Yeast, bitter to 35 IBU using a split between mash, 60min, and whirlpool additions
  1. Saaz
  2. Chinook
  3. Sorachi Ace
  4. Sabro

The Malt Variants

Bitter to 35 IBU with Magnum, Lunar Crush Yeast, SG 1.050
  1. Irish Stout Malt
  2. Floor Malted Pilsner
  • Saaz Hops Feedback: Grassy, dank, tropical, a touch pineapple. Big yeast character, good berry and guava. A little pungent at first, nice and crisp. “This might be my favorite, it's like a light IPA”
  • Chinook Hops Feedback: Fruity, tropical, light pine, light passion fruit. “Clean with light pine and passion fruit”
  • Sorachi Ace Hops Feedback: Super melon fruit. Herbal, earthy. “Lovely, great bitterness and fruity finish”
  • Sabro Hops Feedback: Candy and fruit. Sabro comes through; Citrus, pineapple; This reminds of a really really light IPA. “Like a session IPA, hoppy forward but really drinkable”
  • Irish Stout Malt Feedback: Tropical cream, very slight grapefruit, small grassy flavor (but enjoyable), passion fruit. Clean, light crispy malt and passion fruit, moderate thiol character. “Light Gooseberry and moderate grapefruit Resin-y finish”
  • Floor Malted Pilsner Malt Feedback: Tropical fruit, mango. Light malty, red fruity, ester

Observations from Six Beers Brewed

  • Even without hop addition, thiol strains produce more 3MH, indicating that a majority of thiol precursors are derived from barley.
  • Lightly kilned barleys appear to contain the highest amount of thiol precursors.
  • Hops can also contribute thiol precursors, but to a lesser extent than barley.
  • Even with low hop additions, tasters still referenced IPA impressions of flavors
  • It has been suggested that mash hopping might help convert Glut-3MH to Cys-3MH prior to fermentation, but there are more recommendations against this practice. Berkeley Yeast states that Tropics strains already express enzymes that convert Glut-3MH to Cys-3MH during fermentation, and mash hopping is prone to creating astringent, bitter, and vegetal off-flavors.
Using thiolized yeast strains require no additional process steps or equipment, you can pitch, build starters, and oxygenate just like other liquid yeast strains. This gives brewers new tools in the arsenal for enhancing the punch and complexity of many beers with low-kilned malts and thiolized yeast strains. They also lend themselves as a great option for split batches. So grab some yeast and enjoy some big guava and passion fruit notes!


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