Roasted coffee is made up of some soluble solids and mostly insoluble solids (mainly cellulose) as well as volatiles that are liberated as gases. The composition depends on the species and variety of the Coffee Beans, the Coffee Fruit Processing, the Roasting and Extraction Methods used.
The soluble solids that are dissolved contribute the most to the brew taste and strength. The volatile soluble compounds contribute to its aroma. Caffeine in particular is among the most soluble components of ground coffee and is extracted early in the process.
The insoluble solids and oils in suspension combine to form brew colloids, which contribute to aroma, body and taste. They also alter flavor by trapping and later releasing soluble solids and volatiles. The insoluble solids that are in emulsion are primarily made up of cellulose which contributes to body. The oils from the insoluble solids also contribute to aroma and taste, plus it helps to decrease the perception of bitterness by coating the tongue.