"Quick Pre-boil sour" Lacto pH question

[AaronWesternNY]

I have a split wort batch of Belgian Pale going: half yeast- half unhopped lacto. I grew lacto up from a quart starter from grains at 98F for 3 days before pitching liquid into wort. I took a pH of the lacto half and it is about 3.8, which is where Wildbrews says it "ceases to reproduce." I plan to boil this lacto wort (killing the critters) and pitch it in with the yeast half to ferment it out. Hopefully this will give a "sour" beer...

So... What is lacto converting to lactic acid? Is my lacto still converting it and just not getting more sour, essentially just making more lactic acid? Or, has the pH killed all lacto bacteria making it pointless to continue heating? If the second is the case, and there is no current action, I don't see any reason to continue maintaining the lacto wort at 98 for a couple more days.

Others have tried this approach (thanks for all the good ideas- BBB, Mad F, BN Speedy Kriek thread), but from what I have found they used hydrometer gravities to judge the lacto levels. Lactic acid and alcohol have close to the same density making the hydrometer read the same (or thereabouts), so pH should be used to monitor lactic acid progression instead of gravity, right??

Thanks all.

[Quin]

I did a similar procedure for 12 gallons of Berliner Weisse.
-Standard mash at 150F
-mashout
-runoff
-boil for 5 min
-chill to 130F
-added 2lbs pils malt for inoculation w. lactic bacteria
-covered w/ saran wrap to reduce oxygen
-held around 100F for 96 hours (was at pH 3.7 at 72 hours, pH of 3.6 at 96 hours)
- boiled and added 5 IBUs of Hallertau Mittlefrue
-chilled to 65F and pitched clean ale yeast

Yes, you would use pH to measure "sourness". My OG was still 1.036 after the final boil.

[AaronWesternNY]

Did you saran wrap the outside of a plastic fermenter, or did you find some way to saran wrap the top of the wort-grain mixture? Did yours come out sour as expected?

I don't have any way to purge O2 from the carboy. At day 2 it is bubbling every 10-15 seconds, large bubbles (larger than a quarter). It has a smell that sort of reminds me of the Dutchesse. Do I have 3 gallons of vinegar on my hands?

[Quin]

After chilling to 130°F in the kettle, I pumped the wort back to the mashtun. I criss-crossed layers of saran wrap across the mashtun pushing it down to come in contact with the wort and the sides of the mashtun. I put the lid on and wrapped a couple layers around the outside. I basically followed the process outlined by Will Meyers, Brewmaster at Cambridge Brewing Co. on the sunday session from 11/22/2009.

It turned out very sour, but it still drinkable.

For your batch, you might want to ferment them separately just in case it's acetobacter. You should be able to taste it once fermentation is complete and blend to your liking.