So I have a nice vigorous culture, that I keep in the refrigerator and take out every few days, double with equal weight of whole wheat and water, put half straight back in the 'fridge, and make family bread with the other half. Works fine, nice bread. I've been doing this for quite a while. This culture is healthy and doubles or even triples in six to eight hours. It's about a year and a half hold.
But my bread-eaters would like a change, and especially would like occasionally a lighter bread with mostly white flour. So, I tried upping the white flour proportion, and got... pleasant loaves. But not light or white enough. And somehow the dough didn't seem to be rising as well. So... I decided to "rebuild" my starter culture using just white flour. (Or rather, start a new one, and keep the old one – good call, that!) I mixed up as usual (150g cold wet starter, 75g warmish water, 75g flour), but fed with just the white flour I usually bake with. It rose like about 1/4 and stopped. Hmm, I thought, I guess that culture really doesn't like white flour... let's hope that in a few days of feeding we'll get to a new yeasty communities that does.
So pour away half, feed again. 12 hours later, nothing. A few bubbles.
Pour away half, feed again. Wait 24 hours this time. Nothing. A few tiny tiny bubbles on the top. Still basically 1 cup of nice white flour and water.
Pour away half, feed again. Wait 24 hours again. Nothing! This is wierd, because it seems that the original healthy culture couldn't contribute anything that likes white flour.
Pour away half, feed again, plus a dollop of the whole-wheat starter which meanwhile has eagerly more than doubled despite waiting in the fridge. 12 hours later, nothing. Not even bubbles.
OK, so my question: can flour have some additive or other property that inhibits yeast from growing in it?
FWIW here's what it says on the flour bag: "Unbleached Flour. Enriched Pre-Sifted All-Purpose Flour. Ingredients: white flour (contains wheat), niacin, iron, ascorbic acid, thiamine mononitrate, alpha amylase, riboflavin, folic acid, contains wheat gluten". A long list, but AFAIK those are all pretty standard additives in Canada (and compatible with the designation "unbleached").
(Or am I just impatient? I always had such success with the whole-wheat-fed culture that perhaps I should just wait like 2 days between feedings and two weeks for fermentation to start?)