Originally Posted by PseudoChef
If you're fermenting with Saccharomyces first, then it really isn't going to be a lambic (or a plambic, if you're gonna be anal about it).
Are you planning a turbid mash? That is what is going to leave a lot of the unfermentables available for the wild yeast and bacteria to work on.
Having never done a Lambic before, and being quite terrified of waiting a year and a half and finding out something's not right about it, I'm pretty much following JZ's instructions to a tee. I even emailed him directly to ask about a few things. Me, I'm more concerned with the quality of the beer than with adhering to traditional Belgian technique restrictions. If it means I can't call it a lambic or a kriek, that's cool---it'll be Evan's Oude Sour F*ckin' Cherry Bier. As long as it's a good sour beer.
Anyway, what Jamil says is, unless you plan on blending young and old batches (which I don't, since I don't have a dozen extra carboys to spare for 2 years), this method of weakly fermenting out the maltose with ale yeast first, then getting the bugs to finish the job, gives you the correct sourness without having to worry about blending.