Alcohol boil off and kettle souring

[seancooley]

Hey guys. New to the forum. I've been souring beers for years but did my first kettle sour this week. I pitced Lacto Brevis into 6.5 gallons of 1.045 wort which was in line with my estimates for preboil gravity. It fermented for 48hr between 95-100 degrees and it dropped to 3.4pH. Following the boil I had 5 gallons of 1.042 wort instead of 1.058 which is what I was expecting. If I'm not mistaken Brevis produces ethanol during fermentation. Does this alcohol boil off? Should I adjust my original gravity to 1.042 instead of 1.058? Thanks so much for any insight into this situation.

[brewinhard]

Hey guys. New to the forum. I've been souring beers for years but did my first kettle sour this week. I pitced Lacto Brevis into 6.5 gallons of 1.045 wort which was in line with my estimates for preboil gravity. It fermented for 48hr between 95-100 degrees and it dropped to 3.4pH. Following the boil I had 5 gallons of 1.042 wort instead of 1.058 which is what I was expecting. If I'm not mistaken Brevis produces ethanol during fermentation. Does this alcohol boil off? Should I adjust my original gravity to 1.042 instead of 1.058? Thanks so much for any insight into this situation.

How long was your boil? If it was for an extended period of time, I would have to believe that much of the alcohol produced during the lactic fermentation would boil off. And yes, the Wyeast strain L. Brevis is heterofermentive (produces alcohol, CO2, and lactic acid). Did you pitch a large starter of the lacto strain? If so, that could also have diluted your final OG in the process (but not by that much). I wonder if the lacto simply ate a lot of those gravity points up in the two days (seems like a lot, but it could be possible)? That would be the only explanation I have for this. And in this case, I would adjust the final post boil OG to 1.042.

[seancooley]

Thanks for the response. Boil was 90 mins. Lacto starter was 500ml, 1.020 gravity and on a stirplate for 3 days. Should i put a L. Brevis starter on a stirplate?

[troybinso]

I have had L. Brevis go from 1.054 to 1.020 in 3 days at 100 F

[brewinhard]

Thanks for the response. Boil was 90 mins. Lacto starter was 500ml, 1.020 gravity and on a stirplate for 3 days. Should i put a L. Brevis starter on a stirplate?

Typically lacto starters should be performed with an airlock as most lacto strains do not enjoy oxygen while reproducing. But either way, it sounds like your starter did a great job on its wort duty.