I am vegetarian and gluten free so please offer solutions without meat or wheat if possible! Thank you
There are other vegetable scraps in there too! The cabbage is definitely what’s making it bitter though, first time I’ve made stock including it and it turned out purple and bitter
Some carrots will sweeten it up nicely.
And now that I think of it, a couple of sweet onions would do well. Although your present stock is bitter, I imagine the color is glorious.
Assuming you already removed the cabbage from the stock- you can add an apple or two depends how big your batch is, cut into large chunks and let simmer then taste.
Generally any cruciferous veg isn’t a good idea for stock.
I'm curious if others use cruciferous vegetables in stocks. I never have- always thought that the sulfur they contain would be a bad actor in a stock.