Following Tartine Bread, I've tried twice and each time, inside 2 days there are 4-5 patches of "green stuff" on the top of the culture...stuff smelled like baby puke

The first time I just covered with a kitchen towel and the 2nd time I used plastic wrap. The house is 77-78
o.
Could the flour be bad? I know my white is ok but the wheat could be the culprit...
Could it need to be tightly sealed even though that's not what the book says?
Any thoughts? Thanks!
Mark