Sorry for the wall of text!

TL:DR great brew day ruined by AC shutting off overnight and fermentation temperature skyrocketing. Fixed by brewing the same beer again and choosing a different yeast.

So I had posted a few days ago about weird and wacky ideas for making an Oat-centric beer for a homebrew event in October. I came up with this recipe for my take at an Oat-wine and started making a yeast starter on Monday for a brewday the following day (which was yesterday).

I had been worried that using a high proportion of oats (33.3%) as I was might lead to a stuck sparge so I am happy to report that my combination of a 15 minute beta-glucanase rest at 110°F (43°C) and a hefty 1lb (~450g) of rice hulls was fantastic in preventing this. It was at this point that I encountered my first obstacle.

I had calculated that I would need 2 gallons (~7.6L) of boiling water to bring my mash up to Saccharification temperature but this ended up being not nearly enough. I was aiming for 152°F (67°C) but after adding all the boiling water the mash had stabilized at around 142°F (61°C) so I hastily boiled another half gallon in a tea kettle and added it to the mash which managed to bring the temperature closer to where I wanted it (148°F (64°C)) but at this point the mash was already extremely thin and I didn't want to just keep adding more water so I decided to just roll with it and accept I would have a slightly more fermentable wort and therefore a drier final beer.

After this the brewday was fairly routine. I had planned on an extended boil to bring my final volume down to 2.5 Gallons (~9.5L). I accidentally overdid the boil a little and after cooling down to as low as my ground water could go (71°F (~22°C)) I ended up with only 2.2 gallons (8.3L) in the fermenter. As luck would have it, my yeast starter was almost perfectly the correct volume to bring the wort to the full 2.5 gallons so after oxygenating the wort I pitched the entirety of the nice active starter into the fermenter along with a Tilt hydrometer and closed everything up. My original gravity was 1.087 for an overall brewhouse efficiency of 68% (on the lower side for me but it was a big beer so I had expected this and was pleased with how everything had gone) At this point I cleaned everything up and went home for the night (I brew at work instead of in my apartment).

When I came in to work this morning it was clear the AC had turned off overnight and I could see the airlock on the fermenter going absolutely crazy. I opened up the Tilt app on my phone to check on the stats of the beer. It had only been around 16 hours but the gravity was down to 1.037 and the temperature was at 89°F (~32°C) which was far hotter than the top end of the range of the yeast I was using (Scottish Ale: Optimal range 63–75° F (17–24° C)).

I was able to wrestle down the fermenter temperature by covering it in wet paper towels and blasting the AC and a fan at it but I'm still pretty sure the beer will be an undrinkable fusel alcohol mess that not even an extended amount of cold conditioning time will fix.

Thinking through my options I decided the best course of action would just be to re-brew the batch and go for a different yeast that was more sensible in these temperatures. I had considered using a clean-tasting Kveik strain such as Omega HotHead or Lutra Kveik but I ultimately decided against this because I am of the opinion that even with adequate nutrients and oxygen, the Kveik strains tend to impart an off flavor that I don't like in the final beer. I therefore decided to go in the complete opposite direction and choose a lager yeast which I would ferment around 50°F (10°C) in the keezer we use for serving beer.

At least I could learn from mistakes of yesterday's brew and so today I brewed the exact same beer again and even slightly improved my efficiency! (Original gravity up to 1.089 from 1.087 at the same volume). I was still only able to cool the wort down to around 71°F (~22°C) with an immersion chiller and so the batch is cooling overnight the rest of the way and I'll pitch the yeast tomorrow when I come into work.

I haven't dumped the original batch that fermented too hot so now I guess I'll be able to do a side by side test when both are finished and I'll have another update for you all!