Are you an organic grower? Coffee (unless certified organically grown) is a high-pesticide-use agricultural product, grown in locations where some of the mostly deadly pesticides are still legally used on food crops.

But ANYWAY...I wouldn't think that the chaff would have the substance you'd require to build up a bed. It would make an interesting soil amendment, though. Is it already composted?

It's terrific to find a local source of organic waste products that needs to be disposed of. I would dearly love to make use of the cotton gin waste so plentiful in my location, but can't because of the extremely high pesticide use for that crop. ;-(

Raw coffee is highly acidic. Blueberies and azaleas love it. You will need to lime your bed extensively if you are not seeking to acidify the soil.

I think it is a great idea Boo.