Dough Turns Brown and Smells Bad
I'm a newbie to sourdough and am on my 8th or 9th attempt yet I've had a really hard time to get a decent sourdough loaf. I believe my starter is strong, I feed it regularly and before I mix it in I always do the float test--and it does, even after a few minutes. Where I think I'm stuck is the bulk fermentation stage. My kitchen is usually fairly cool (70°F) so I get that it'll take time for the dough to get at least 1 1/2 times the size. But after 36 hours, it didn't quite get to 1 1/2 times (I put 1/4 cup of dough in a 1/2 cup measure so I could have an easier time telling). The dough smelled like nail polish with the top of the dough turning a brownish colour. The starter is at 100% hydration and I get the same sort of result whether I use unbleached all purpose flour or bread flour (I don't like whole wheat or rye).
With earlier attempts using shorter times, I always get a really sticky dough (even if I go up on the flour or down on the water) and so I get a flat, dense baked loaf. I'm determined to get it right but I'm running out of ideas...