Final Ph for a sour-mashed Kentucky Common?

Hey guys, I'm going to be making my second attempt at a sour mashed Kentucky Common in a couple days and am trying to go about things a bit more scientifically this time.

Last time I brewed one I did a whole mash sour mash for 36 hours and ended up with a pleasant sourness, but a body that is much too thin for my liking (and I think for the style as well seeing as it is basically a dark cream ale).

This time I am thinking of either doing a whole mash sour mash for 24 hours or sour mashing 20% of the grist for 48-60 hours and adding it back with the sparge of the rest of the batch. Thoughts?

One thing I'm wondering about and can't seem to find an answer for is what the final ph of the beer should be. Judging from the ph of other sours and considering that a Kentucky common is only lightly soured (if at all) I'm thinking somewhere in the range of 4-4.4. What do you all think?

Any comments or suggestions about the process?

Cheers!

Sour mashing is a technique that is intended to make it possible to brew with very high alkalinity water, as is found in the limestone regions of Kentucky. You can take the souring either to a point where you achieve a typical beer mashing pH somewhere around 5.2 to 5.6 or you can take the mash pH quite a bit further down. In the first case, there wouldn't be a lot of tartness. But there is the possibility that you would taste the lactate ion that remains in the wort from the partial souring. In the second case, you would likely create more tartness along with the lactate taste.

When you sour the mash into the typical beer mashing range, the wort body and mouthfeel is similar to regular mashed beer. If the mash pH is very low, the fermentability of the wort will go up and the body will go down. For the Kentucky whiskey producers, they don't care about body, but they do care about fermentability and the total alcohol produced. They are more likely to sour a mash more than a beer brewer should.

Thanks for your reply Martin, very informative. After some more research I'm thinking of souring 20% of my grist for 48 hours and then adding enough back to take my mash ph to 5.2. Based on my water profile here and my malt bill I'm estimating that my unadjusted mash ph will be 5.6 (using your excellent spreadsheet).

After the mash I'll add some more (possibly the rest?) of my soured mash portion with the sparge water. I'm imagining a post-boil ph of 5-5.2 will get me where I want to be. My last Kentucky Common ended at 3.9ph and had the thin body I mentioned. I'm hoping this shift in method will remedy that.