Souring technique taken from:
http://sourbeerblog.com/designing-brewing-berliner-weisse/
Step Mash: 15 minutes at 130° F, 60 minutes at 155° F, then 5 minutes at 168° F.
Boil wort for 15+ minutes, then cool to 95° F and transfer into Lactobacillus fermentation vessel, or leave in kettle if kettle souring. As an additional precaution, it is recommended to pre-acidify the wort to pH 4.5 with lactic acid.
Pitch an appropriately sized Lactobacillus culture of your choosing. Hold at the preferred temperature, usually around 100 to 110 F, for that strain until you reach your desired pH. (The Lactobacillus I chose was the blend from Omega Yeast, which sours quickly at lower temps, I held at 85 for almost 48 hours and it the tartness was perfect) Transfer wort back to boil kettle or re-fire kettle with souring wort already inside. Boil for 90 minutes.
Cool wort to 62° F, oxygenate, and pitch healthy starter of German Ale / Kolsch yeast at an appropriate cell count, a starter is suggested. Ferment at 62° F for 5 to 7 days. Optional Cold Crash