Fast souring with WLP672 - yeast infection???

[Danp3d]

Hi folks,

I've decided to try to brew my first sour beer - a Kriek-inspired beer, but a bit of a chimera (it's more like a cherry infused sour trippel).
Thing is, I don't have the patience to let it sit on a demijohn for a year, so I decided to just do a fast souring process (common for berliners).

What I did:
- Mashed as normal;
- Boiled for 15 minutes to sanitize and get rid of DMS;
- Cooled it to ~ 30°C and transfered to a fermenter (being careful not to splash it around to avoid oxygenation), left a very small headspace;
- Used some lactic acid to drop PH to 4.5 to prevent wild yeast infection;
- Pitched some wlp672 (Lactobacillus Brevis);
- Kept it at 30°C to ensure optimal conditions for the lacto (give it a bigger chance of fighting off any eventual yeast trying to run the show).

The idea was to let a lacto-only fermentation go until it reached a PH of ~3.5, then boil it again to kill the bugs, add some hops and pitch some WLP001 to kick off the alcohol fermentation. Drop some cherries on the secondary and be happy.

Well, I got home this evening and found a very vigorous fermentation, with a big layer of krausen on top of the beer and the airlock overflowing like crazy. Cleaned it up and placed a blowoff tube, but that's a pretty bad sign: a lacto-only fermentation shouldn't be producing all that CO2.

Question is: is anyone here familiar with WLP672? Did White Labs really just screw me over by giving me a Saccharomyces-infected Lactobacillus culture?
I'm seriously disappointed at this. Unsure if I should just dump the batch or ride it out and see what happens.

 

[Danp3d]

Damn it. A quick Google search showed me that apparently both Lacto cultures from Whitelabs are usually infected with yeast. From what I've seen, it's usually better to dump probiotic yoghurt into the wort than to use WLP672 for fast souring.

Oh well. I guess I'll just have to boil it and make a fake sour by dumping more lactic acid in. Sad.

 

[hirschb]

Do not boil it!!!!
You have a wild yeast infection and alcohol has been produced. If you boil, the alcohol will boil away, and you'll be left with sour water and no sugars for your yeast. It's better to ride out the fermentation. If the infection is gross, dump it. BUT, if the resultant beer tastes/smells ok, go with it. I've had two failed/infected berliners (bad seal on my souring keg) that turned out quite nice with additional time and/or fruit additions. The important thing is to test the beer. Let it ride for a few weeks, see what the taste/smell/pH are, and go from there.

 

[TheWiggman]

I don't agree hirschb. For rapid souring (do a web search or check this excellent post here) you want to boil, 'rapid sour' at ~45°C, then do a final boil to kill off the bugs/stop souring. There are still plenty of sugars left in the wort to finish the brew with yeast and turn it into a beer.

 

[Danp3d]

The lacto managed to inactivate the yeast! Got home from work and found a very different scenario: the fermenter was completely dead. Not a sign of fermentation.
Checked the SG - it dropped a few points (from 1.062 to 1.058) but the pH dropped significantly: from 4.5 to 3.7. considering pH is logarithmic, that's quite a big drop.

That's definitely a pH most yeast strains can't handle, so I guess I was saved by the bell.

Lessons learned:
1. Do not use WLP672 for fast souring again. It definitely is infected by Saccharomyces. I'll get a Lactobacillus Plantarum probiotic next time.
2. Lactobacillus is a beast

I guess I can stick to the initial plan: I'll let it sour a tiny bit further, reboil it (probably tomorrow morning, considering how quickly the pH is dropping) and pitch some clean yeast. Hooray!

 

[Danp3d]

Do not boil it!!!!
You have a wild yeast infection and alcohol has been produced. If you boil, the alcohol will boil away, and you'll be left with sour water and no sugars for your yeast. It's better to ride out the fermentation. If the infection is gross, dump it. BUT, if the resultant beer tastes/smells ok, go with it. I've had two failed/infected berliners (bad seal on my souring keg) that turned out quite nice with additional time and/or fruit additions. The important thing is to test the beer. Let it ride for a few weeks, see what the taste/smell/pH are, and go from there.

That's actually very good advice, thanks mate!
I got lucky - the yeast got suppressed fairly quickly, and I wasn't brewing a Berliner (it was a fairly high gravity beer), so I'll still be able to stick to the plan and do a second boil (which is good, I didn't add any hops to the first boil to favour the lacto).