How Much Sugar Is Consumed By Lacto During Kettle Souring?

[kdw2pd]

After a conversation I had with a pro brewer here in town, I'm trying to understand how much sugars from wort are consumed during the kettle souring process. Briefly, I kettle-soured a gose (50% pils, 50% wheat, pre-acidified to pH 4.5 using lactic acid) using the Omega Lacto Blend for about 48 hours. I don't have a pH meter, but it tasted quite tart. For the sake of argument: Let's assume I ended up where OYL-605 generally does, 3.3-3.2 or so. Don't have notes, but I think I saw a drop in gravity of 2 or 3 points (1.04 to 1.037 or so). FG of 1.01, for an ABV of 3.5%.

My brewer friend suggested that my gravity reading, indicating a drop of 2-3 points was wrong because lactic acid is denser than water. As acid is produced, it would appear to increase the gravity of the solution. The bottom line being: more than 2-3 points of sugar were consumed.

So: is 2-3 points worth of sugar sufficient nutrients for lactobacillus to drop the pH from 4.5 - 3.2, suggesting I had an accurate gravity reading, or is he right that the density of lactic acid renders those calculations inaccurate?

 

[bschot]

Yes, the specific gravity of lactic acid is 1.17, I think the lactobacillus ate more than 2 or 3 points. I think if you had a pH meter to read final pH and then you could calculate how much lactic acid you have in solution and then could account for it in the gravity change. I'm not sure how difficult of a calculation it would be but it sounds like a fun thought experiment.

 

[specharka]

There are some strains of LAB that are capable of heterofermentative metabolism, but their efficacy is quite limited compared to Saccharomyces. I would consider the increase in density due to the production of lactic acid to be a non-factor, as the actual concentration of lactic acid is on the magnitude of parts per million. It doesn't take a math whiz to figure out this increase is negligible. What is more likely is your lacto blend probably contains some heterofermentative strains of LAB (or might be contaminated with yeast). If your gravity drops more than a point, I would guess there was some fermentation happening.

 

[kingschiff]

sorry to kick up an old thread but got no response on my post.

https://www.homebrewtalk.com/forum/threads/goodbelly-ate-insane-amount-of-sugar.660229/

can anyone shed any insight?

TL;DR: Tried goodbelly for the first time as kettle sour lacto. After boil my gravity was down to 1.027 from 1.056. This has never happened when I used OYL-605.

 

[day_trippr]

An actual yeast infection seems most likely...

Cheers!

 

[RPh_Guy]

Definite yeast contamination. I replied to your other thread.

 

[kingschiff]

I'm not sure how I've done this process 5 times with OYL-605 and never had this issue,but first time using goodbelly I did?

Either way, enough for me to just spend the extra money on the OYL-605.

Really appreciate the input/science.

 

[kingschiff]

Definite yeast contamination. I replied to your other thread.

would you agree that I can use my pre boil OG safely as a benchmark to get an estimated ABV?

 

[RPh_Guy]

would you agree that I can use my pre boil OG safely as a benchmark to get an estimated ABV?

No, the post-boil gravity is the only meaningful OG.
The alcohol was boiled away.

 

[Tombstone0]

No, the post-boil gravity is the only meaningful OG.
The alcohol was boiled away.

It depends on how long the boil was. If it was just brought to a boil to pasteurize I would use the original gravity, if it was boiled for an hour use the post boil gravity.

 

[RPh_Guy]

It depends on how long the boil was. If it was just brought to a boil to pasteurize I would use the original gravity, if it was boiled for an hour use the post boil gravity.

Maybe, but in this case it went from 6 gal to 4.75 gal post-boil (look at his other thread).
The alcohol is gone.

 

[kingschiff]

yeah full hour boil, volumes are correct above. thank you guys.