Some members of my family are lactose intolerant, so I am planning to mash at a higher temperature to reduce fermentability (and increase residual sweetness from the malt.) By my math, the lactose should be about 2.5% of the total sugar in the wort.
If the original target mashing temperature is 153*, what temperature should I mash at to increase non-fermentables by 2.5 percentage points? There's a BYO Magazine article that says 158* is the upper limit, but gives no indication of how large an effect it will have.
PS - on REAL vs IMITATION vanilla, I suggest trying to find a copy of the issue of Cooks Illustrated which explains that the main flavoring chemical in vanilla is "vanillin," which is identical in real and imitation vanilla. However, real vanilla contains a variety of subtler and far more volatile components which are easily driven out by heating (like the aroma in aroma hops, which you add at the end of the boil.) For anything you heat (like cookies), you will not be able to tell the difference. Whether the volatile components in real vanilla will survive six weeks of fermentation and conditioning is a mystery to me.