My newly set up microworm cultures always have a yeasty odor and a faint acid odor. As they age and get productive the odor gets a little stronger but one that needs throwing out can turn your stomach in a hurry. A 2 week old culture is probably at its most productive stage and still has a fairly mild odor. I use 2 parts cooked oats and 1 part rice baby cereal as the basic ingredients with a small addition of yeast to start processing the starch into food for the nematodes. If you start a new culture from an old one and move enough of the liquid containing the nematodes to the new culture, you don't need to add any yeast because some will be transferred from the old culture with the nematode start itself.