I do all grain, so can't help much with partial mash.
If you are going to infect with lactobacillus, there are the questions of when and how. Here is what my research has yielded.
For the How: The ways are 1) Doing an actual sour mash (~ 48 hrs at ~100-120* F) to combine with your grist in the mash tun 2) Inoculating wort with a culture 3) Throwing some grains into the new wort before (or after too, I guess) fermentation. My bet is that a sour mash in a controlled environment is probably the best tasting but least reproducible way, so a lot of folks just use the culture. Also, most do a 15 min or less boil (yikes!) so that there are still bacteria cells all up in there from the mash. And, I have heard that bacteria do not like high oxygen levels, so I didn't bother with the Ox stone for either batch. Lastly, proper BW should have very high carb level (I think around 3.5 volumes).
For the When: regarding inoculation, the question is before or after primary fermentation. If you don't give the bacteria much sugar to work on, they'll take a long time. I see some folks cellaring their berliner weisse for 8 mo or a year. I tried it both ways. Made the same recipe twice. First I inoculated after primary fermentation was finished, the second I inoculated immediately and didn't pitch brewers yeast until 4 days later (really wanted it to sour) and after all was said and done, blended the two.
Hope this helps. I have to disclaim that I don't really love BW. I really love darker sour beers like Flanders, etc. but not BW so much. I tried a commercial version too and didn't finish it. Thought I would love it cause I love yogurt, but BW just tastes 'spoiled' to me. It could very well be my version, as it was a huge experiment. But after having the commercial version, I think I'm moving on.
The second batch that did 4 days of just lacto at 95*F was pretty funky. It's still drinkable but funky. The first batch was like a light quaffing beer.
