worms eat decomposer microbes more than the organic material, and coffee grounds in my experience don't hold moisture well enough to become microbially active for a very long time - in the compost, the heat can break them down somewhat faster, but also there's so much more "off gassing" there that you just lose the smell faster .... I also think that the reason folks think coffee grounds "disappear" fast in the compost is they blend in so well :)

I've found the best way to cycle grounds thru the worm bin is to mix them with the carrot pulp I sometimes get from a juice bar, seems to get things attractive fast, and the finely ground carrot alone is really attractive to them

Bill

Bill, for what it's worth I find that in my hot bin coffee grounds get hot FAST. Even in the worm bin they seem to warm it up, and one experienced wormer I know says you have to be careful adding these, because too much can get so hot so fast it'll kill the worms.

Since heat comes from decomposition I'm thinking that actually the coffee grounds support microbes pretty well. In fact I've got another possible problem that I'll go into in another post: ammonia smell, which I think means the worms are being overfed.

you might find that your compost gets hot fast, but that doesn't mean the grounds are getting hot - coffee grounds are difficult to keep moist enough to have any microbial decomposition take place, and in fact are only about 1.5-2% N according to all the figures I've seen - meaning if adding coffee grounds heats up your compost, what you need is more coarse materials to provide areation, and I'd bet that coarse sawdust might do as well

I've composted large amounts of coffee grounds for long periods [from coffee bars], and have held coffee grounds, with filters [Carbon] in buckets and get no reaction other than all the water settles out, and sometimes mold grows on top if it stays damp - the molds are an indication of hi carbon material .... high N materials, like fresh grass clippings, never stay inactive in buckets, but turn into a stinky mass that heats quickly and loses heat quickly

the ammonia smell is from the anaerobic digestion of N, which could be overfeeding, but more likely lack of air with excess of N in a mass

Bill

Bill, in composting terms coffee grounds are generally considered "greens," with a C/N ratio around 20. (Regular food scraps are about C/N 15, and dried leaves are about C/N 50-70.) So I think there's plenty of N in them.

As for the heating effect, I don't know what to tell you. A load of coffee grounds in my bin heats it up like nothing I know of other than grass clippings.