A foul odor or yeasty smell like bread dough means an infection is brewing and your dog should see the vet as soon as possible. (dogster.com)
Im now on my 5th cycle and still getting a very yeasty smell.. (herbangardener.com)
If it's starting to have that familiar yeasty smell, foam up and swell, it's good and you can add it to your recipe; if it's stagnating and not getting foamy or rising, throw it out. (gfjules.com)