Hi all. I’m 2 weeks into fermenting a pale ale with WLP002. The sample I pulled today tasted pretty good but had a mild banana flavor that I wasn’t expecting… but not bad.
My OG was 1.055 and my FG was 1.012 which is lower than I expected. I used a big pitch of slurry from a previous batch so I’m pretty sure I pitched plenty of yeast. I purged the headspace with pure O2 and shook it for about 4 minutes. My fermentation temp I think might be the issue. I pitched at about 65F. It went up to about 68F by day 2 and then 72-73F on day 3.
Do you think the banana ester is more likely from the higher ferm temp or from under aerating the wort? Since my FG was low, I’m inclined to believe its temp.
Any thoughts?
Assuming that the yeast was clean when you pitched it, I’d guess that the low 70’s temp created the banana. I use WLP002 a lot and it can get estery when fermented in the low 70’s, although by day 3 that temp should have had less effect that if it were earlier. I’ve not had that ester with 002 before so I don’t know it if will age out with a little time. 78% attenuation with 002 is a little high but not a major delta.
Do you have any experience with this strain? Is this something new that you haven’t picked up before? I’m grasping at straws here, but I get a pear ester from it that could possibly be taken for banana.
Or maybe it could be a combination of diacetyl with other esters combining to give that impression? Warm ferm temps plus an oversized pitch seem like a recipe for a D-bomb with 002 unless you rouse the yeast frequently and bump the temperature at the end of fermentation.
I doubt you underoxygenated your wort for that beer, if anything you could have overshot depending on how much headspace your fermenter has.
A warm fermentation plus a little underpitching would do the trick.
Banana is the compound known as amyl acetate, which is the condensation product of 1-pentanol (five carbon atoms, C5H11OH) and acetic acid. The alcohol 1-pentanol is one of eight pentanols that are known as amyl alcohol. It is also a component of fusel alcohol.
Truth be told, a lot of British strains are POF+ (phenolic off-flavor positive) and throw amyl acetate when the conditions are right (a few throw sulfur as well). These compounds are usually a sign of stress.
You’re a genius and I love you.
I pitched about 150ml of yeast slurry, pretty much all the yeast I recovered from a previous batch 2 weeks ago so I think I probably over pitched if anything. Temp wise I pitched at about 66f end let it slowly rise over three days. I didn’t really intend for it to get above 70f but it went to about 73f on day 3. Could possibly be a pear flavor. It’s pretty subtle but is a fruity ester of some sort. I’m hoping that another week in the yeast will help. This is actually only my second time using 002. My other batch is in bottles but didn’t have a fruity eater flavor which is why I was curious if his strain was prone to this.
Overpitching can be stressful for the yeast, combined with higher temperature. I doubt that leaving it on the yeast at this point will do a whole lot in terms of elimination of that ester, especially if it is fusel-related. Next time don’t pitch so much and control those temps with a swamp cooler and you will be fine.
+1 Having great minds on this forum is a real bonus.
While I suspect that the temperature was a little too high, another aspect that could create yeast stress is if there weren’t enough micro-nutrients in the wort. I brew with RO water and have recently started using yeast nutrient at the recommended dosage to help assure that my zinc level is somewhere around the right level.
Martin, let’s say I were to do a RO + nutrient vs. RO sans nutrient xBmt, is there a style you’d recommend that might allow any differences to be more prominent?
I’ll bring up something that no one else will:
Did you use any extract? I find stale extract to exhibit a banana-like flavor and aroma in finished beer. Not sure if anyone else in the world picks up on this. It’s part of the infamous “extract twang” as far as I’m concerned.
If you didn’t use extract, then nevermind the above comment. The other guys are probably right.
I am not a genius. I have just passed Malcolm Gladwell’s 10,000 hour threshold. 
This was an all grain batch. Martins post about nutrient is quite interesting though. I do build water from RO and this is the first time in a long time that I did not use yeast nutrient. Interesting.