Can yeast absorb or consume isovaleric acid?

[javert]

Right now we are dealing with issues across three batches of IPA... they have a cheese flavor that didn't happen our first batch. Since we don't intend to sell a new style called Kraft(TM) Beer, we are struggling to deal with the cause:

• All three batches were fermentated with a sachet of Safale S-05. The second and third were pitched usen the yeast we cropped from the bottom of the first one.
• All three have been fermentated in a chamber of about 19 ± 2 °C. To be fair, other batches from other styles haven't have this issue.
• We have used new packs of hop pellets sent by delivery on a nonrefrigerated box (Galena for bittering and Amarillo for flavor).
• This cheesy off flavor has been diminishing as days pass while the beer is on the bottle.

At first I believed it could be dyacetil but after realizing the taste is more of cheese than popcorn flavored butter, I'm suspecting the hops might be the culprit. I've read that isovaleric acid is a by product of hops aging. Is the yeast able to absorb and methabolize isovaleric acid?

I'm making a hop tea this evening to make sure. I hope it's the hops, because the other possibility - a pediococcus infection or a weak yeast - are far more difficult to deal with.

 

[microbusbrewery]

Assuming it really is isovaleric acid, I don't think sach can metabolize it. Brett can reportedly break it down into more appealing compounds (e.g. see http://www.milkthefunk.com/wiki/Isovaleric_Acid). Brett can also produce isovaleric acid. How did the hops smell before you added them to the boil? If they didn't smell cheesy, I'd probably suspect some kind of brett or bacterial infection (staph or strep), but I don't believe pedio will do it. I'd start with a thorough cleaning and sanitizing. I'd also go with a new pitch of yeast since your current one is suspect. Smell your hops before you use them to make sure they're not contributing to the problem.