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).
In general, when everything is working, we see a drop over 48 hours down to 105°F (41°C)–110°F (43°C) and pH about 3.7. Then we rack post-acidification into barrels where the temperature will drop pretty quickly. Because you’re coming from the high side on the spectrum, the formerly dormant wild yeasts kick in pretty quickly.
We brew our Berliners on the fringes of the brewing season, early to late September through early November and then in spring around the end of March into May. There’s a lot of spontaneous yeast activity before the first frost and then once the trees are in bloom.
The benefit for us, over traditional spontaneous fermentation, is that we have a good, palatable beer earlier, about 7 or 8 months. That’s when the Brettanomyces starts to show itself a little bit, and that’s where this beer shines. Our lambic-style beer, on the other hand, at 8 months still has residual sugars, might not have developed acidity, and might have some astringency or bitterness from elevated hopping rates.