http://www.notsoprofessionalbeer.com/2013/09/brewing-with-yogurt.html (http://www.notsoprofessionalbeer.com/2013/09/brewing-with-yogurt.html)
You can make Kefir beer also but it has a short window before it turns totally sour.
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With this method you sour the beer before the boil so there is no bacterial in it to continue to sour it
Ron P had a blog post about historic beers from north Germany fermented with lacto from yogurt.
I've heard of people using priobiotics for this on US boards.
So who's going to man up and do this as an experiment then?
I used WLP 677 (White Labs lacto culture) in a gose last year.
I made a starter in 3 litres of wort - last July during the warm spell - and incubated them as warm as I could.
I put the starter in a cardboard box lined on the inside within polystyrene and tinfoil. I cut a hole in the roof and put a desk lamp on top and I put a black material cover over the starter.
Excellent thread here, talks about this, and sour mashes and yoghurt cultures:
http://forum.northernbrewer.com/viewtopic.php?t=43587