What if Pate Fermentee is more than 3 days old?

I have read that 1 to 3 days is the right time for a pate fermentee.  I have a chunk in the refrigerator that is a week old.  Is it still good, but not optimal, or will it make foul bread? What happens after three days that makes it unfit? (Sourdoughs seem to keep longer and be okay)