Sucrose

Sucrose is important to the taste of sweetnessSweetness is an important positive quality in fine coffees, and is one of five basic tastes: Sour, Sweet, Salty, Bitter, Savory (Umami). In coffee, sweetness is a highly... in light roast coffees, as it is completely converted or destroyed in darker roasts.: Sucrose is largely destroyed by the roasting process through various reactions and thermal caramelizationA reaction involving sugars that occurs during coffee roasting. A caramelized sugar is less sweet, but has greater complexity of flavor and aroma. Caramelization is slower than Maillard.... 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 crackAn audible popping sound heard during roasting. In coffee, one refers to "first crack" and "second crack," which come from two different classes of chemical reactions.: An audible.... These are the chemical reactions, occurring at approximately 356 degrees F, that are exothermicA term applied to thermal reactions, referring to one that releases energy. A classic example is burning. Most parts of the coffee roasting process are endothermic, but first.... Once caramelization 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 affected by the presence of water, ammonia, and proteinaceous 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.”