As an experiment, for my first attempt, I'm making a small batch of sauerkraut. Small like less than 1/3 of a head. Its setup is pretty amateur, no professional airlock. Anyway, it's been going for a little while, less than a week, and I wanted to taste a little bit to see how it was going. It is starting to taste a little bit sour, which I think is good, but also has a very noticeable yeasty taste and smell. I don't see any visible signs of yeast, no kahms yeast film on the top or anything(and the cabbage is, as far as I can tell, completely submerged). I plan to leave the kraut for longer before calling it "finished", and to be entirely honest, I don't really know what sauerkraut is ideally supposed to taste like. Should this yeast thing be worrisome?
Well, now you've increased the odds of a variety of things you don't want, because you opened it up "to try some" and never had it all that well sealed (according to what you wrote - I don't use "professionally separating fools from money" airlocks either, but I seal my kraut jars to keep air out, and I leave them that way for a good 6 weeks, so I have no idea what it tastes like at one week, other than it would be horribly underdone) so it's been exposed to oxygen, which promotes a variety of spoilage in kraut.
If the cabbage is fully submerged, seal it as well as you can (a properly tightened canning jar lid works, plastic wrap and a rubber-band can also work) and put it away in the dark for 5 weeks at 50-65°F before you revisit it.
I stepped up the low-budget airlock game on the most recent batch and put 4 sealed canning jars into a plastic bucket - it catches the mess if I improperly oversealed a jar (didn't happen, but I'm cautious that way) and also makes a secondary containment for carbon dioxide to help keep oxygen out.
I had one jar earlier that was prepped with insufficient weights available, so it got some kahm yeast on top when the cabbage rose above waterline. Being properly sealed from air, it only got kahm yeast, and that was easily removed with the top layer of kraut when it was done. I specifically opted not to bother trying to deal with it when first seen, since that would allow air into the jar. I have taken more care with weights since.
Edit: You can either add (if you have space) or replace some of the current liquid with (if you lack space) plain carbonated water (which will release carbon dioxide and help flush air out of the container) to reduce the impact of having opened it, so long as you then cobble up some sort of airlock.