Possible citric acid production by brett
A long while ago on this board I put forward a theory that citric acid/esters *might* be produced by brett, with some impact on beer flavor.
This theory was prompted by certain strains in yeast culture collections being labeled as citric acid producers, some patents on citric acid production via brett, and use of the word "citric" to describe certain beers with brett in them.
That's not much to go on and I hasten to add that I think this theory is a long shot. If I had to bet, I'd bet against it.
However, I recently had a chance to run it by Dr. Verachtert from KU-Leuven, author of many fundamental lambic fermentation papers over the years. He said they did not really look for citric acid, and may not have found it even if it were there. I got the impression he thought it was unlikely but possible, and certainly an open question.
I'll repeat my occasional call to anyone out there who might have the capability--if you could test for citric acid/esters in some oude gueuze that would be great! (and maybe publishable)