The short question I want to ask is: will my beer be okay sitting on a yeast cake for 2 months at temperatures intentionally warm? I'd like to get it up to 90F if possible, to allow resident bacteria to continue to sour the beer.
The rationale is as follows:
I'm brewing a sour Leipziger Gose. 1 week before brewday I made up a 1.5L starter of White Labs lactobacillus delbruckii. I used my Fermwrap to keep the starter warm, and it definitely did the trick - the starter was decidedly sour, a little vomity almost (but in a good way).
On brewday I pitched the entire lacto starter into my 1.055 OG Gose wort. I only cooled my wort down to 90-100F or so, and used my Fermwrap to keep it warm. I allowed the lactobacillus to ferment the wort for 1 week WITHOUT any yeast. The lactobacillus brought the gravity of the brew over the course of the week down to ~1.048. Not as much attenuation from the bacteria as I thought I'd get, but the beer did taste slightly-moderately sour (but definitely still sweet since there were still quite a bit of fermentables). I should mention that this beer only got about 5.1 IBUs of hops, so the hops shouldn't be limiting the lacto...
After the week with warm lactobacillus-only fermentation, I cooled down the carboy to ~65F or so, made up a 1L starter of Wyeast German ale yeast, and then pitched that in. As of now, the Gose is very nicely fermenting along.
The heart of my question is, after the saccharomyces is done fermenting, can I then crank up the heat of the carboy up to 90F again and allow the lactobacillus to continue eating any residual fermentables for another month or two? My worry is that the yeast cake sitting around for 2 months at 90F won't do good things for the flavor. Will heat increase the rate of autolysis, if autolysis even occurs at all on my 5-gallon homebrew scale? Unfortunately, transferring the beer to a secondary isn't really an option since all my secondaries are full at the moment.
I'm also aware that after the alcohol is formed from the yeast fermentation, the lactobacillus will be further inhibited in their souring potential, so this could also be a problem... When the yeast is done, it will probably be in the 4.5-5% abv ballpark...
Thanks for your help!
The TL;DR: Will keeping 5 gallons of beer on a yeast cake at 90F for 2 months make bad things happen?