This is a seriously interesting question! Definitely one for the Brewmasters!
We’ll do some more research on this for sure, but for anyone who’s interested in the ultra-simplified version: When the yeast eat the hop oils in your wort, they can sometimes transform them into entirely different chemical compounds than they were initially, which can drastically change the hop aroma and flavor profile in your finished beer. The idea of actually harnessing this process to purposefully affect the flavors of your beer sounds like it would be incredibly complex.
We’re also really interested to know if any of you have dabbled with this process. We’ll admit, this one might be over our heads!
This is a really interesting question. I’d love to see empirical evidence of biotransformation. For now, it seems like people are saying if they do things differently, the beers tastes different. On the surface, that should be expected. The magnitude of the difference is surprising, so maybe there’s something going on. Hop aromas come from the types of oils in the hops (humulene, myrcene, caryophyllene, and farnesene). These can be measured in hops using a (very expensive) spectrometer.
Since hops are valuable because of their oil I had a quick look into studies on another charismatic oil – olive oil. It looks like yeast can interact with oil to create carbonyl compounds and polyphenols, changing the sensory perception of the oils. Different yeasts affect oil in different ways (see link).
It looks like biotransformation may really be a thing, but that the type of transformation will likely depend on the essential oil profile of the hops being used and the type of yeast (or yeasts) doing the fermenting.
I would love to see the results of an experiment where the brews were analyzed using a spectrometer to see the difference in expected vs observed essential oils in different experimental batches, and to see if new aromatic chemical compounds were created. But, I think a good experimental next-step would be to take hop oil extracts, add different types of yeast to them, and then see what happens.
I haven’t been here in quite some time but it looks like quite a bit more has been written about biotransformation but the bottom line is you need yeast to do the work. I’ll just quote one article but they all seem to agree:
“If you want to take advantage of biotransformation, which can lead to more of a rose/citrus/fruity aroma from the conversion of geraniol to citronellol, add dry hops early in the fermentation process while the yeast are still present and active.”