Reference for Guinness Sour Mash?

I hear a lot of talk on this board about how Guinness employs a sour mash for their beer. I don't really pick up any lacto sourness in it. I made a clone doing the simple 70/20/10 grist and their house ale yeast that had sort of a tartness that I could see as people attributing to a sour mash - but I got this without doing a sour mash. I am just a casual member of this board, but I've never actually seen anyone point to a source that says Guinness actually uses this technique. Can somebody hush the voice in my head that is telling me this is all just from speculation and rumors and post a link?

From a variety of sources, they sour 10% of each batch and then pasteurize before blending. You could also sub sauer malt

http://media.www.jhunewsletter.com/...Science.Behind.Brewing.Guinness-2247170.shtml