I am interested in getting opinions on the differering flavors of a sponge vs. that of a poolish. In my bread baking books the authors talk about a sponge (at a 64% hydration and a fermenting temp of 40- 55F) which is supposedly more acidic than a poolish (at a 100% hydration and a fermenting temp of 55-70 F.  Both preferments I let develop for 14 hrs. I a NOT expecting a real serious sour, like a sour dough. I am, however, expecting a very subtle sour flavor. I have tried both preferments numerous times but I can not taste a bit of difference.  Any idea why? thank you