I need some help with this one. I haven't experienced this in the past and generally I have been problem free with my finished beers for the most part. But the past 3 batches have had a varying level of a rubbing alcohol flavor/aroma. I brewed 3 batches back in Sept which 1 of them came out fine while the next two in a row had this rubbing alcohol flavor and aroma. I at first pinned it to the yeast I used. It was Omega Amercian Ale and it was the first time I used it. But now a few months later, I brew a Robust Porter using US-05 and upon tasting the hydro sample at kegging Im hit with the same off flavor/aroma. Now, it is only slight but enough to remind me of what I tasted previously. I do not like this trend.
My question is what kind of infection (if that could be the problem) would cause a rubbing alcohol character? We can rule out high fermentation temps, I use a chest freezer with a Johnson Controller. These batches fermented 66-68*. And for that, I can see 1 batch maybe but not 3 in a row. The 2 prior batches with this partial mash batches, this last one was all grain...so it's not limited to a certain process. Not much has changed, no new equipment, process, hoses...etc. I use filtered tap water and campden tab...shouldn't be a problem there. This is something new, never had this before in 6 yrs of brewing.
The common demoninator with all 3 batches is my boil kettle, I transfer to the fermenter at the end of the boil via tubing and oxygenate with pure o2. I thought maybe I have been over oxygenating, but again never a problem before this. It would take excessive use of pure o2 to increase fusels. And to me this isnt' so much fusel, it's more rubbing alcohol. I use PBW and Starsan. It's not a fermenter problem, each batch used a different fermenter. All other factors seem ok, good mash, good boil, hitting my numbers. The ph's are good, FG's..etc. Just a slight rubbing alcohol flavor and aroma. What can be causing this?