Thanks for the writeup-
What’s the alpha (and beta, for that matter) concentration for the hops you used in the WP, and what utilization percentage did you assume for the WP? We use 5%, for our 8 min WP and 15 min hop stand. |
Oh, and did you take the pH of the LAB culture or the wort right after you added the culture? It’s possible that the drop you saw at 7 hours was just due to the pH of the inoculant you used. |
Sorry for the string of posts-
To answer your question, YES, over acidification can hurt the cells. Essentially, many LAB can survive at low pH but might not be growing much once the pH get down. So, if the cells have time to replicate (thus resulting in more cells) when the pH is higher, the total glycolytic flux of the culture could be higher at low pH due to increased cell yield, even when the cells are not actively dividing anymore.
As an aside, I think this is why chalk is so effective at increasing the cell counts in starters of many LAB. There is more than enough sugar around to make lots of cells, but if the pH drops too much the cells quit dividing. Buffer the pH up with chalk, increase the number of doublings possible before the pH drops too much, and you get to pitch more cells into your wort later. Which hopefully results in more rapid acidification. |
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Originally posted by CLevar
Thanks for the writeup-
What’s the alpha (and beta, for that matter) concentration for the hops you used in the WP, and what utilization percentage did you assume for the WP? We use 5%, for our 8 min WP and 15 min hop stand.
Citra was 13.4 AA, Galaxy 13.5 and Simcoe 12.0
No info on beta acids from LHBS. I assumed zero utilization since the whirlpool was performed at 165 F. |
Originally posted by CLevar
Oh, and did you take the pH of the LAB culture or the wort right after you added the culture? It’s possible that the drop you saw at 7 hours was just due to the pH of the inoculant you used.
I thought of that after the fact, but no I didn’t take pH just after adding the inoculant. That very well may be the case. |
Originally posted by CLevar
Sorry for the string of posts-
To answer your question, YES, over acidification can hurt the cells. Essentially, many LAB can survive at low pH but might not be growing much once the pH get down. So, if the cells have time to replicate (thus resulting in more cells) when the pH is higher, the total glycolytic flux of the culture could be higher at low pH due to increased cell yield, even when the cells are not actively dividing anymore.
As an aside, I think this is why chalk is so effective at increasing the cell counts in starters of many LAB. There is more than enough sugar around to make lots of cells, but if the pH drops too much the cells quit dividing. Buffer the pH up with chalk, increase the number of doublings possible before the pH drops too much, and you get to pitch more cells into your wort later. Which hopefully results in more rapid acidification.
Super interesting...Thanks!
So I guess I can rule out any more acidification. My plan going forward is to pitch a starter I have of wyeast 3724 Saison and add some brett dregs of commercial beers and eventually age on some fruit puree.
Sorry I couldn’t give more substantial results. I’m still a n00b at these kind of experiments, but really have a lot of fun trying!
Cheers! |
Originally posted by joeneugs
It was a 90 minute boil and I added .25 ounces of Polaris (18%AA) at 60 minutes for around 7 IBU’s supposedly under the threshold for lacto, especially a hardy strain like Plantarum. What was the volume on this batch? Also, though a cool experiment, L. plantarum is VERY hop-sensitive, so even 7 IBUs would completely inhibit it. If you were to repeat the experiment (it would kick ass if you did), I’d either use unbittered wort or a different strain of lactobacillus, like L. brevis, which is more hop tolerant. Not much, mind you, but more, none the less. |
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Originally posted by HornyDevil
Originally posted by joeneugs
It was a 90 minute boil and I added .25 ounces of Polaris (18%AA) at 60 minutes for around 7 IBU’s supposedly under the threshold for lacto, especially a hardy strain like Plantarum.
What was the volume on this batch?
Also, though a cool experiment, L. plantarum is VERY hop-sensitive, so even 7 IBUs would completely inhibit it. If you were to repeat the experiment (it would kick ass if you did), I’d either use unbittered wort or a different strain of lactobacillus, like L. brevis, which is more hop tolerant. Not much, mind you, but more, none the less.
Yep. Thanks for the info. I heard that you should be ok with a hopped wort as long as it’s below 10 IBU’s, but like you say, plantarum is an exception. This was a 5.5 gallon batch. According to sourbeerblog, this is usually the case with any probiotic based source of lacto. Completely hop intolerant. I will do this experiment again since I like doing kettle sours, and hopefully next time I’ll be better prepared. Thanks for all the help guys! |
A little update here-
I started a culture of a bunch of different isolates: L. paracasei, and delbruekii, 3 different Pedio. spp, a Leuconostoc, and 2 different L. lactis strains into 10P wort at ~70F plus or minus a "whirlpool" hop addition of 5g/L of a ~6.5% beta hop . The culture was unable to acidify the hopped sample below pH 4.3 in the time it took for this mixed culture to get down to a pH of ~3.5 (from a starting pH of ~5.4) in the unhopped sample.
Some of these strains are known to produce compounds inhibitory to other organisms, which may explain the slightly higher final pH and somewhat sluggish acidification in the unhopped sample. I am going to play more with this once I have all the strains up at the same time (plus a handful of new-to-me LAB I recently isolated from a sour mead), decreasing the WP hop addition to something hopefully more manageable.
Combined with the available literature on inhibition of Gram’s positive bacteria by beta acids, I think its safe to say that what I observed initially for the single isolate is a general rule.
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Just had a phone call with a senior tech from Hopsteiner. He’s suggesting that it is alpha acids NOT beta acids responsible for the inhibition that I am seeing. (Note that I wrote alpha acids, not iso-alpha acids). Specifically, he indicated that the solubility (or lack thereof) of beta acids makes them a less likely candidate than alpha acids. I hope to try some of their products to narrow in on what is inhibitory.
In any case, continuing to talk only about iso-alpha acid seems to be complete and utter folly at this point. |
