The basic chemical reaction of coffee knowledge during coffee roasting.

Many thermal and chemical reactions take place during baking: decarbonation, dehydration of quinic acid, fragmentation, isomerization, polymerization, and complex sugar reactions (caramelization). The main thermally reactive components are monosaccharides and sucrose, chlorogenic acid, displaced amino acids, and trigonelline amide. Both aravinose and calactose in polysaccharides are transferred, and basic sulfurization involves hydroxyaminolysis. Carbohydrates are polymerized and broken down simultaneously, and depending on the degree of baking, 20-30% of polysaccharides are broken down, releasing heat-labile monosaccharides.

Sucrose: Disaccharide consisting of half D-glucose and half D-fructosyl.

Sucrose is the main sugar in coffee. The melting point of pure crystalline sucrose is 320-392 degrees Fahrenheit (160-200 degrees Celsius), with an accepted melting point of 370 degrees Fahrenheit (187.8 degrees Celsius). Degraded dry sucrose can have a melting point as low as 194 degrees Fahrenheit (90 degrees Celsius), and with dehydration and concentration, the sugar begins to break down into glycoside conjugates. Between 338 and 392 degrees Fahrenheit (170 and 200 degrees Celsius), caramelization begins. It is at this point that the water and carbon dioxide break up and the resulting outgassing causes an explosion. These are chemical reactions that occur at about 356 degrees Fahrenheit (180 degrees Celsius), which are exothermic reactions. It is very important that once the caramelization reaction begins, the coffee does not release heat (heat), otherwise the coffee will taste "baked" in the cup. One possible explanation is that the coffee beans being heated are exothermic, breaking long polymeric chains and allowing the broken chains to connect to other components. Sucrose and its subsequent conversion to components, or caramelization, are determined by the presence of water, ammonia, and proteinaceous substances. Heavy baking will show a higher degree of caramelization than light baking. The degree of caramelization is a good measure of baking and has a high resolution.

Cellulose: A Long Linear Polymer of Anhydroglucose Units

Cellulose is the main fiber in coffee cell walls. This is partially ordered (crystalline) and partially disordered (amorphous/amorphous). The amorphous regions are easily affected and reactive, but the crystalline regions are packed tightly and hydrogen bonded, almost completely unaffected. Natural cellulose, or cellulose I, is converted into the isomeric forms cellulose III and cellulose IV when heated. The structure of coffee is a well-developed matrix, which improves consistency in quality and helps to spread heat evenly during roasting. Cellulose is present in coffee as embedded in lignocellulose (an amorphous matrix containing hemicellulose and cellulose-containing lignin), which forms the cell walls of the matrix. Hemicellulases are polysaccharides composed of branched sugars and uronic acids. Lignin is particularly noteworthy because it is a highly polymerized aromatic substance. When the distribution temperature exceeds 446 degrees Fahrenheit (230 degrees Celsius) and the surface temperature of the beans exceeds 536 degrees Fahrenheit (280 degrees Celsius), severe damage to the cell wall occurs. The actual temperature varies depending on other factors. The second explosion associated with deep baking is the breakdown of this matrix, possibly accompanied by volatilization of lignin and other aromatic hydrocarbons. Under controlled roasting conditions, the ambient temperature of the beans should never exceed 536 degrees Fahrenheit (280 degrees Celsius). A slightly wider safety margin should limit the maximum ambient temperature to 520 degrees Fahrenheit (271.1 degrees Celsius). These temperature limits minimize damage to the cell matrix and increase the complexity of cup performance, baking yield and product shelf life.

Trigonelline: A nitrogenous base found in coffee

Trigonelline is 100 percent soluble in water, so it ends up in the cup. Fenugreek amide is the main ingredient responsible for excessive bitterness. When the beans are at 445 degrees Fahrenheit (229.4 degrees Celsius), about 85% of the fenugreek amide degrades. At this temperature, beans appear to be moderately baked. For lighter roasts there is more fenugreek amide and therefore bitterness, but less caramelized sugar at this temperature. Caramelized sugar is less sweet in the cup than uncaramelized sugar, so when baked properly, the two ingredients complement each other to make it taste better. The melting point of pure crystalline fenugreek amide is 424 degrees Fahrenheit (217.8 degrees Celsius), and fenugreek amide begins to degrade at about 378 degrees Fahrenheit (192.2 degrees Celsius). Degradation of fenugreek amide is one of the key control markers for determining optimal response ratios.

A member of the carboxylic acid group.

Melting of pure crystals of quinic acid begins at 325 degrees Fahrenheit (162.8 degrees Celsius), well below the temperature of the baking environment. Quinic acid is water-soluble, exhibits a slight sourness (not the bad taste of fermented beans) and a sharp quality, which imparts more character and complexity to the cup presentation. It adds cleanliness to the finish of the cup as well. It is a stable compound at baking temperatures.

Nicotinic acid: member of the carboxylic acid group

Melting of pure crystals of niacin begins at 457 degrees Fahrenheit (236.1 degrees Celsius). Natural nicotinic acid is bound together with a polysaccharide cellulose structure. During baking niacin develops into soluble form. Regardless of the degree of roasting, high levels of niacin were associated with good cup performance. Because it's 100% soluble, it's going to end up in the cup. Niacin contributes to good flavor acidity and a clean finish. Its derivation rate is a key control marker that can be used to determine the temperature at which the reaction rate is optimal, as well as chemical propagation rates. In addition, the interaction of melted niacin with other components can significantly increase the brightness of dark roast coffee (in the cup).

ambient temperature

The temperature of the baking environment determines the occurrence of certain types of chemical reactions. There is a temperature window where baking produces a good flavor response and produces ideal cup performance. Temperature values outside this window negatively affect classic cup performance. Even if the temperature value is within the window, different temperatures can change the characteristics of the cup, which gives the roaster room to develop a personal style or a desired style, or to tame the personality of a certain coarse mineral in the coffee, while still controlling the related quality to the best.

system energy

At any given ambient temperature, the BTU and the transfer efficiency of the baking system will determine the rate at which a particular chemical change occurs. At higher energy and transfer rates, the reaction proceeds faster. The reaction rate also has a window within which the quality of performance in the cup can be optimized. This is called the optimal reaction rate, abbreviated as BRR.

Optimum reaction rate (BRR)

The best cup characteristics occur when the ratio of fenugreek amide degradation to nicotinic acid derivation remains linear. The governing model for this reaction rate is the time/temperature/energy relationship. Ambient temperature (ET) establishes the pyrolysis region in which the desired chemical reaction occurs, while energy value (BTU) and system transfer efficiency (STE) determine the rate of reaction propagation and linearity of the ratio of nicotinic acid derivation to fenugreek amide degradation. Because the density of green beans varies widely, the distribution of reactions will vary for any given ET / BTU / STE format. For higher density beans, it takes longer to achieve comparable consistency. Monitoring the temperature of the beans at this stage of baking is a good way to make the reaction distribution similar. The ideal ambient temperature, ET, for best response ratio, BRR, is from 401 to 424 degrees Fahrenheit (205 to 218 degrees Celsius), with 405 degrees Fahrenheit (207.2 degrees Celsius) being the default. The BTU required is determined by the system's transfer efficiency, or ability to transfer energy to the beans.

Maximum Ambient Temperature (MET)

The protocol for establishing the ideal baking thermal environment is a balancing act. Although it is desirable to maintain the BRR temperature and energy level until the reaction target is reached, the BRR temperature will be much higher than the caramelization temperature of sucrose. Because many roasting systems use a simple temperature regulation mechanism, these systems exhibit thermal hysteresis effects, so be careful not to let the coffee exothermic. It is also important to limit the maximum ambient temperature, MET. As mentioned earlier, it is important to maintain the structural integrity of the cellulose matrix. Lower temperatures reduce surface evaporation of components and minimize capillary action that draws components to the surface and volatilizes them off. Hydraulics, an effect of internal pressure directly related to the temperature of the beans, are already at work. By limiting the maximum temperature, losses will be minimized and the essence of the coffee will be preserved. Therefore, MET should not exceed 520 degrees Fahrenheit (271.1 degrees Celsius). The roasting system is based on MET values, which are the actual final beans, or lower bean temperature, related to the degree of roasting.