How soluble are coffee grounds in water?

I would say that we extract from the bean much like we extract from the grain in brewing but neither is soluble. Things like antioxidants, caffeine, proteins, and tannins are extracted and with malted grains carbohydrates are broken down into sugars by the very enzymes that were created by the plant during malting.

So I mean protein will give body, roasting gives aroma/flavor but the cellulose plant cell structure is not soluble.