I've been working on sours recently. I'm happy to share a recipe, but here, I think the process is more important. The BIAC is perfect for kettle souring in that everything the bacteria is touching in the souring process is going to be boiled - keeping everything clean. Here's my simplified process:
Mash as normal - perhaps leaving a bit more dextrines if I want to play with Brett later - I usually shoot for a 13G batch so I can put the extra 3 gallons in a better bottle for long term fermentation.
Give a quick boil to kill off
all bugs - clean slate
Drop the temp to ~110F
Adjust the pH (lactic acid addition) to 4.5 or lower to inhibit unwanted bacteria (enterobacter - poo)
Blow CO2 back through my plate chiller/pump into the bottom of the conical to not only clear the lines, but blow off unwanted O2 and make a nice CO2 blanket on top (looking to discourage aerobic bacteria fermentation - acetobacter - vinegar).
Pitch bacteria (been mainly using L. Plantarum - Goodbelly or Simpson's - ~150B cells - use a starter or loads of SuperShots) seal and install a blow-off tube, set the temp control to 110F and let 'er rip for a day or two.
Once pH and taste are where I want them (~3.5-3.7 for my tastes - 24-48 hours - samples from the racking port), I'll rack off any live wort to a better bottle for Brett fermentations for more bugs for longer, funkier fermentation.
Bring back to a boil to kill everything, add hops, and proceed as with any other sacch. fermentation in your BIAC (I roll mine into a home made temp chamber). I haven't been brave enough to put Brett in the BIAC on the cold side yet. Anyone else try this?
I usually take down all my BIAC components every 5 brews (valves, pump, heating element, etc) and then run a cycle with PBW. After a kettle sour, though - unless I'm doing another sour next, I will break every everything down for a thorough clean. May not be necessary, but just a habit. Haven't soured a clean beer unintentionally ... yet.
This forum has been great and talked me into buying my BIAC back in 2015. I have about 60 batches through it so far, so yes, still brewing with the BIAC
Kent
ps. Nathan is awesome!