Sucrose


Sucrose

Sucrose is largely destroyed by the roasting process through various reactions and thermal caramelization. It is destroyed at this rate: 2.9% remains in a light roast; 0.9% in a medium roast, 0% in a dark roast. Sucrose is sweeter before caramelization, but perhaps more aromatic after caramelization. Still, if there is no sweet taste, the perception of caramelized sucrose will not be sweet. "Sucrose is the principle sugar in coffee. The melting point of pure crystalline sucrose is in the 320-392 degrees F with 370 degrees F most commonly accepted. Degradation of dry sucrose can occur as low as 194 degrees F. and begins with the cleavage of the glycosidic bond followed by condensation and the formation of water. Between 338 and 392 degrees F, caramelization begins. It is at this point that water and carbon dioxide fracture and out-gassing begins causing the first mechanical crack. These are the chemical reactions, occurring at approximately 356 degrees F, that are exothermic. Once carmelization begins, it is very important that the coffee mass does not exotherm (lose heat) or the coffee will taste "baked" in the cup. A possible explanation is that exothermy of the charge mass interrupts long chain polymerization and allows cross linking to other constituents. Both the actual melting point of sucrose and the subsequent transformation, or caramelization, reaction are effected by the presence of water, ammonia, and proteinatious substances. Dark roasts represent a higher degree of sugar caramelization than light roasts. The degree of caramelization is an excellent and high resolution method for classifying roasts."

See also: Trigonelline