I need to start with the caveat that pre-acidification doesn’t always work the way you hope. But it might actually be easier on a homebrewing scale than how we do it here at The Referend.
It all comes down to temperature. This is our spontaneous pre-acidification process for our Berliner Messe: We make wort at area breweries, let it cool (to about 120°F/49°C) in the coolship for 4–5 hours, then bring it to the blendery where it’s held warm for 2–4 days (until the temperature drops to 90°F/32°C–105°F/41°C), and finally rack it into barrels for spontaneous fermentation.
Generally, the idea is to hold the wort warmer than yeast can be active but at a temperature where Lactobacillus can be active. In our experience, it’s a little risky, and it’s in the 105°F (41°C) up to 130°F (54°C) range. So we rack out hot into insulated totes (we’re also experimenting with the insulating power of wood) and simultaneously monitor the temperature drop and the pH drop (which is also extremely variable).