NKB

seven days ago - I baked my usual two loaves of NKB which turned out to have a sour taste. I commenced a new batch - everything the same and after the suaul 20 hours of doing what it does - the dough has a sour smell - I used a new bag of flouor same brand - everything else is the wame. Anyone has any idea please - I miss my lovely smelling bread

Gerry