Now that I'm all grain I've done many experiments regarding differences in grains, trying to make 2 batches identical in every way except for one variable with the grain.
However I just learned via brewersfriend that a yeast starter with a month older yeast than another yeast starter results in drastically different cell counts.
I.e, with a 1.6L starter at 36 gravity using the Braukaiser equation
75 days = 278 billion 105 days = 257 billion
which is a 7.5% decrease relative to the younger yeast.
In general, does a cell count difference of 10-20% have a material effect on the outcome of the beer for tasting purposes, and therefor invalidate any tasting experiments one may do?
I can always mix the yeast together before adding them to the starters, of course.