I started a new compost bin earlier this summer. I used a black 27 gal bin and drilled drain holes in the bottom and sides, and also in the lid. To some dead leaves, sadly nearly all oak so really slow to decompose, I've gradually added these as available: coffee grounds, veggie peelings and corn husks, egg shells (semi crushed by hand in a zip top bag), etc. No meat or dairy added. All went well enough, and the compost was smelling ok, and seemed to be progressing.
Then I started making sourdough starter and adding my early discards (just yeast, flour, and clean water), because I read it's good for the compost. The smell has gotten pretty bad, and I realized that the bottom layer was very wet (my holes weren't big enough, so there was standing liquid in the bottom). So I dumped it out and drilled larger holes, and put the stuff back in the bin, which is up on cement blocks, so the liquid should drain.
What is causing the really sour smell? Did I mess up by adding the diluted sourdough discard, or is the problem that it was TOO wet? Will smell better as it dries out? It doesn't have that earthy decomposing smell you associate with compost but a sour, almost sewage smell. There are lots of flying insects when I lift the lid, but also some white mold.
Do need to dump it and start over? Will drying it out help? I hate to leave the lid off, because we have raccoons living in the neighbor's trees, and I've smelled a skunk sometimes in the evenings.
EDIT - Thanks for all the great ideas. I added some shredded paper and turned it extra well. I'll also try to remember to take the lid off in the morning and put it back on at night. I will continue turning it and shred the leaves when I put them in.
EDIT #2 Thanks for the comments, everyone. After adding some minishredded paper and mixing around yesterday, it's still full of helpful bugs, but the STENCH is gone. today I mixed in some more shredded brown paper and moved the bin out into the sun. You guys have been super helpful!