Gravity when pitching yeast: 1.016
PH when pitching yeast: 2.3
After 24 hours, the wort + sour starter was going nuts. A white pellicle covered the entire top, and lots of CO2 was coming off. The pellicle was there in the morning, but when I went back in the afternoon to take a picture, it was mostly gone, but you can still see a bit on the edges:
After reading a bit more about different Lacto strains, it seems most of them are heterofermentative, even the strains from the yeast labs. My pre-boil gravity was 1.028, and when I checked the wort, it had dropped to 1.016 and the pH was down to 2.3. Lactic acid has pretty much the same gravity as sugar. The gravity drop was most likely due to the lactic acid producing alcohol. It tasted fine, a bit sour, but still pretty sweet. I think once it's done fermenting it'll be pretty puckering.
Here's the bit that I did differently from most Berliner Weisse recipes. Most Berliner Weisses aren't boiled, or are only partially boiled. Since my pH was plenty low, and since I had no idea what other nasty bugs I may have cultured from the grain, I chose to boil a little under half of the wort, and pasteurize the rest.
The half I boiled got the hops, then after a 30min boil, I added the rest of the wort and held between 145-150*F (That's 63-65 for the Centigrade folks) for 30min. The process is called vat pasteurization, and should provide a 3-log kill (99.9%). You can pastuerize faster at higher temperatures, but since my bugs made alcohol too, I didn't want to boil off all the alcohol of an already low-gravity beer.
After I chilled it, I pitched about half of a yeast cake from a batch of Koelsch. This is definitely overpitching in normal circumstances. With the low pH, I was worried about poor yeast performance.
I was quickly running out of daylight last night, so I didn't get a lot of pictures, but here's one of my setup. Bayou Classic KAB-4 burner, 60qt pot, little March pump, and a homemade immersion chiller.