Fermentation Question

Hi All, I brewed one of my go to recipes (American Amber Ale, all grain) that I've brewed several times in the past with great results. My last batch had a creamier taste with a vanilla under tone which was not present in the past and I'm trying to pinpoint what caused the change. Still a great beer, just a bit different.

Some details:
- My efficiency was better this time (75%) where in the past is was typically 60%.
- Mashed at 150 deg for 1 hour.
- Room temp was kept at 70 deg as in the past using WL001 California Ale yeast.

Thanks for any advice!

Sounds like phenolics from fermentation to me. Some yeast strains have enzymes that will react with acids that can be found in the malt and create a vanilla-like aroma which is often perceived as a flavor. Also, 70 degree room temp might be a little on the high side as the temperature in the fermentor is likely 5-7 degrees higher. Ferment in a cooler location next time and make sure you pitch the proper amount of yeast (use mrmalty.com pitching rate calculator). Also, the higher efficiency likely lead to higher OG and higher FG which would leave that fuller body "creamier" impression. Finally, if you didn't change anything from previous batches, but your efficiency somehow went up, that would leave me to believe that the crush of the grains was a bit finer that could also contribute to increased extraction of the acids from the malt and the resulting phenolic.

Could aerating the wort affect this as well. Typically I aerate for about 40 min with a fish tank pump, stone and filter.

Thanks,
Bob

The amount of dissolved oxygen you could obtain using a fish tank pump is very unlikely to be enough to cause any problems... now if you were pumping pure oxygen, then I would say it was a definite possibility. My only other "guess" with your pump would be if it's pumping in some funky air from contaminated hoses or some nasty environmental air from where you did it.