I almost always brew 6 or 11 gallons of beer so that I can keep the last 1/2 gallon or so that I throw into a growler. This allows me to throw any dregs, that I dont want to throw into my barrel, into the left over wort. Doing this it allows me to grow up any organisms that are present in any commercial sours. I also have a small incubator that I throw the growler in so I can heat them up to promote bug growth (esp since it is starting to get cold where we are).
The Mad Fermentationist - Homebrewing Blog
is a member of the fourm and also an amazing read on anything and everything sour ales. I am just in aww of his work and am wanting to try some of his recipes soon.