What is the normal attenuation for sour wort (specifically Berliner Weisse)?

Question

I brewed a kettle-soured Berliner Weisse with an OG of 1.034. After two weeks fermenting at around 70 (raised to 72 at the end) with a packet of Safale US-05, it got down to 1.014, apparent attenuation of 58%. The malt bill is also about 7% acidulated malt. Mash temp was low, about 148. Souring was done in the kettle with some unmilled malt, insulated, kept at 100-110 for about 48 hours.

I've read that that the low pH can lead to low attenuation like this. I'm wondering - what are normal attenuation rates for ale yeast in sour worts with high-acid/low-pH? I've also heard of people hitting attenuation in the 80s with Berliners as well.

Answer 1

I used to mash-in my berliner at 150 F, and then just let it cool down to 120 F or so. From there my souring process was pretty much identical to yours. But, I usually pitched straight L delbruckii, with a followup pitch of WLP630 or some other ale yeast(s). With multiple organisms at work, there's more potential for attenuation, and I would always see the equivalent of 80% - dry enough that we didn't worry about it, to say the least.

One trick I always liked: throw in an active starter of champagne yeast, and let it run. This will get your berliner dry!

I don't have much experience with US-05 - Fermentis claims it'll do 81% apparent attenuation, but I understand that in practice 70% is more in the range of reasonable.

One observation: did you take a pH reading? Not knowing the exact mash bill/story, you might just be assuming your wort is/was highly acidic, though with that much acid malt I guess it's probably the case!