Northern_Brewer
British - apparently some US company stole my name
As I mentioned before, this was a split batch fermented with different yeasts, so things like hop age and water profile are all controlled for. One might hypothesise that yeast with a reputation for preserving hop aroma like Chico don't touch the hop oils much whereas eg British yeast with a reputation for muting hop aroma are doing all sorts of things to the hop oils at an enzymic level, so you get a soup of derivatives at a lower overall level of perceived hoppiness, since some of the derivatives won't taste of anything.
I wasn't actually looking for biotransformation, I was just trying to get to know some of the yeast in this thread. I think I was just lucky that Chinook gave such a clear result. I haven't got my notes to hand but broadly it was a 17 litre batch bittered to 25IBU with EKG then 6g/l Chinook and a fag-end (maybe 1g/l) of old Amarillo that had been kicking around the freezer, across copper/WP/dry. That single batch of wort was then split into 4x1 gallon and the following yeast added :
M36 - classic Chinook grapefruit. Call the intensity of this baseline as 100%
T-58 - almost pure lime (with the pepper etc on top) but say 80% intensity
WB-06 - little hopppiness and pretty much swamped by the wheat-beeriness
M36 with pinch of T-58 & WB-06 - intensity at maybe 10-20%, so pretty subtle, but a lovely complex mix of different citrus and hints of floral, with no one flavour dominating
Grapefruit is a classic Chinook tasting note that typically comes from thiols like 3SH, lime is typically a mix of terpenols such as linalool, geraniol, and β-citronellol - these are hop flavours not yeast flavours. Yes, if you wanted to do this "properly" you would do controls without the Chinook to see if M36 produced grapefruit without hops, and T-58 produced lime without hops - but I think we can say that it's a fair assumption for these purposes that these flavours come from the hops?
So the only variable to change was different yeast strains, and we're seeing a change in hop flavours. As one might expect, as the nature of the flavour changes away from the classic Chinook flavour, the intensity of hop flavour decreases. I know it's only one data point, so it's not definitive, but this looks like biotransformation to me.
It's hardly a wild claim, it's not like claiming that yeast can paint the Mona Lisa, we know that lager yeast (descended from cerevisiae) can do specific things to hop terpenols. But you're welcome to try and find an alternative explanation, and to repeat the experiment - that's how science progresses. Even better if you have a GCMS. It's not exactly hard, just take a sample of wort next time you mash in (or boil up some extract), throw in some Chinook, then split and ferment with different yeast. I'm sure lots of people on this thread have open packets of T-58 and WB-06, so you just need a sensible baseline control like US-05 or M36.
You don't want yeast for this style destroying hop compounds, which is what biotransformation is. Something like WB-06 would make a terrible yeast for NEIPAs on its own. So you don't want too much biotransformation - but it seems that the "best" strains(or yeast blends!) are "Goldilocks" ones that do it a little bit, to give a bit of complexity. A number of people have compared Conan with 1318, and the general conclusion seems to be that aside from the yeast flavours, Conan gives a slightly "brighter" "pure" hop flavour whereas 1318 is a little bit muted in comparison but more complex. Some people like one, some the other - there's no "right" answer.
For instance, Scott Janish tested Giga GY054-Vermont versus 1318 in a beer with bittering plus ~5g/l whirlpool of a Citra/Mosaic/Simcoe blend. He found the Conan gave "huge sticky orange lifesavers aroma" whereas 1318 was "more of an orange sherbert with a slight lemon/lime thing...but turned down about 20%". That's interesting that it's so close to what I saw with T-58 (80% of the intensity with lime, despite the different hops).
So my hypothesis is that some ale yeasts do show biotransformation, but not all, in the same way that some humans are good at sprinting or chess but not all. Interestingly both T-58 and probably 1318 are not mainstream brewery yeasts, they're both in a small group of slightly weird yeasts that includes the bread yeasts. S-33/Windsor and (probably) Danstar ESB are also in that group, so they need testing. Conversely I would guess the "hop-forward" US yeasts like US-05 don't biotransform, and it seems Conan doesn't (much) either. Wouldn't it be fun if the "ultimate" yeast for NEIPAs was US-05 with a pinch of bread yeast, the sheer ...cheapness... (in all senses) of it appeals!
I thought IPAs were just beer. Beer is for drinking with your mates whilst you set the world to rights. End of.
But if you want to be picky, (almost) all beer relies on the transformation of certain hop compounds into isomerised alpha acids, so I can't see that you can be too purist about the transformation of other hop compounds. It's a debate you get more in the wine world, is the job of the winemaker to show off the characteristics of his grapes with as little intervention as possible - or is he just trying to make the tastiest possible wine?
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