If you harvest the yeast from an IPA fermentation, you’ll notice that it carries a lot of bitterness. Yeast absorb (or perhaps adsorb) a lot of bitter compounds during fermentation. In his handout, “10 Factors to Making Better Hoppy Beers,” Vinnie Cilurzo of Russian River Brewing Company lists yeast pitching rate as critical factor in making an IPA or double IPA — pitching too much yeast will remove too much bitterness from the fermenting wort. This gave me an idea — what of you “fed” the yeast bitter compounds when you raised them, so they didn’t remove so much bitterness during the main fermentation?
The most abundant bitter compounds in wort are iso-alpha acids. If yeast remove bitterness from beer, they must do so either by taking in iso-alpha acids (absorbing them), becoming coated with iso-alpha acids (adsorbing them) or a combination of the two. If you could fill or coat your yeast with these bitter compounds in your yeast starter, they should remove less bitterness from your main batch. There’s just one drawback — yeast reproduce.
In properly pitched wort, yeast reproduce 3 to 5 times before they reach fermentation density and stop budding off daughter cells. Thus for every yeast cell pitched, there will be between 8 (3 replications) to 32 (5 replications) yeast cells in the wort at peak wort density. If we assume that every time the yeast reproduce, the level or degree to which they are filled or coated with bittering compounds is halved, every time the yeast reproduces, fresh capacity to absorb or adsorb bitterness is created.
For this idea to work, you would need to raise the yeast in a very hoppy yeast starter, then pitch enough yeast so that they only replicated 3 times. In fact, you might want to overpitch to the degree that the yeast only reproduce twice. If full/coated yeast only reproduce twice, they should remove only 3/4 of the amount of bitterness compared with “normal” yeast.
At this point, this idea is pure speculation. Would it work? There’s one way to find out. A simple way to test this hypothesis would be to brew an IPA or double IPA, and split the wort into two carboys. Make two yeast starters, one with no hops added and one highly hopped (over 100 IBUs, calculated). Pitch both carboys at twice the recommend pitching rate and wait to see if there is any difference in the final beers.
If this works, brewers could make maximally bitter beers by simply changing the way they raise their yeast.