How to make very sour base beer for blending?

You might try using a lacto strain with low-to-no hopping. I pitched 1 vial of lacto and half a pack of S-04 for my only berliner weiss. It got pleasantly sour, and very sour after fruit was added. Do the same thing without the S-04 and I assume it would be more sour (regardless of fruit). I think low hops is key. Never worked with pedio.

 

You could do a sour mash and just let it go. I got side tracked and let a sour mash go for five days. It was lip puckering sour.

 

I did the same thing. 4 days of lacto at 110F and the beer is bracingly sour, in a way which unless you like Warheads, you won't like this beer.

 

For my Flanders I kept about 5 gallons of it w/ Roselare in a bucket. Because of the oxygen permeability of the bucket versus my barrel, the bucket is way more sour than the barrel. The increased permeability may produce a little more acetic acid (esp if acetobacter takes hold), but since its a Flanders, and the barrel has no acetic character, the beer in the bucket provides a great way to top up and get a little more sourness in there and a touch of acetic acid.