Basic chemical reactions in the roasting process of coffee in both Chinese and English

Original text:

Basic Chemical Reactions Occurring in the Roasting Process

By Carl Staub

Sourced from the SCAA Roast Color Classification System developed by Agtron-SCAA in 1995

Many thermal and chemical reactions occur during the roasting process: decarboxylation, dehydration of quinic acid moiety, fractionization, isomerization, polymerization, and complex sugar reactions. The principal thermally reactive components are monosaccharides and sucrose, chlorogenic acids, free amino acids, and trigonelline. Both aravinose and calactose of polysaccharides are splitoff and the basic sulfur containing and hydroxyamino acids decompose. Carbohydrates both polymerize and degrade, liberating thermally unstable monosaccharides decomposing 20-30% of the polysaccharides, depending on the degree of roast.

Sucrose: Disaccharide of d-Glucosyl and d-Fructosyl Moieties

Sucrose is the principle sugar in coffee. The melting point of pure crystalline sucrose is in the 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, carmelization 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 carmelization, reaction are effected by the presence of water, ammonia, and proteinatious substances. Dark roasts represent a higher degree of sugar carmelization than light roasts. The degree of carmelization is an excellent and high resolution method for classifying roasts.

Cellulose: A Long Linear Polymer of Anhydroglucose Units

Cellulose is the principle fiber of the cell wall of coffee. It is partially ordered (crystalline) and partially disordered (amorphous). The amorphous regions are highly accessible and react readily, but the crystalline regions with close packing and hydrogen bonding may be completely inaccessible. Native cellulose, or cellulose 1, is converted to polymorphs cellulose III and cellulose IV when exposed to heat. Coffees structure is a well developed matrix enhancing the mass uniformity and aiding in the even propagation of heat during roasting. Cellulose exists in coffee imbedded in lignocellulose (an amorphous matrix of hemicellulose and lignin containing cellulose), making up the matrix cell walls. Hemicellusloses are polysaccharides of branched sugars and uronic acids. Lignin is of special note because it is a highly polymerized aromatic. Severe damage occurs to the cell walls of the matrix at distributed temperatures above 446 degrees F and bean surface temperatures over 536 degrees F The actual temperature values will change due to varying levels of other constituents. Second crack, associated with darker roasts, is the fracturing of this matrix, possibly associated with the volatilization of lignin and other aromatics. Under controlled roasting conditions, the bean environment temperature should never exceed 536 degrees F. A wider safety margin would be achieved by limiting the maximum environment temperature to 520 degrees F. These temperature limits minimize damage to the cell matrix and enhances cup complexity, roasting yield, and product shelf life.

Trigonelline: A Nitrogenous Base Found in Coffee

Trigonelline is 100% soluble in water and therefore will end up in the cup. Trigonelline is probably the most significant constituent contributing to excessive bitterness. At bean temperatures of 445 degrees F, approximately 85% of the trigonelline will be degraded. This bean temperature represents a moderately dark roast. For lighter roasts there will be more trigonelline, hence bitterness, but also less sugar carmelization. Caramelized sugar is less sweet in the cup than noncaramelized sugar, so when properly roasted these two constituents form an interesting compliment to each other. Trigonelline melts in it's pure crystalline form at 424 degrees F Degradation of trigonelline begins at approximately 378 degrees F.. The degradation of trigonelline is one of the key constituent control flags for determining the best reaction ratio.

Quinic Acid: Member of the Carboxylic Acids Group

Quinic Acid melts in pure crystalline form at 325 degrees E, well below the temperatures associated with the roasting environment. Quinic Acid is water soluble and imparts a slightly sour (not unfavorably as in fermented beans) and sharp quality, which adds to the character and complexity of the cup. Surprisingly, it adds cleanness to the finish of the cup as well. It is a stable compound at roasting temperatures.

Nicotinic Acid: Member of the Carboxylic Acid Group

Nicotinic Acid melts in pure crystalline form at 457 degrees F. Naturally occurring Nicotinic Acid is bound to the polysaccharide cellulose structure. Nicotinic Acid is also derived in soluble form during roasting. Higher levels of Nicotinic Acid for any given degree of roast are associated with better cup quality. Since it is I 00% soluble, it will end up in the cup. Nicotinic Acid contributes to favorable acidity and clean finish. It's derivation rate is one of the key constituent control flags for determining the best reaction ratio temperature and chemistry propagation rates. Additionally, the interaction of melted Nicotenic Acid with other constituents contributes significantly to the intensity associated with darker roasts.

Environment Temperature

The temperature of the roasting environment determines the specific types of chemical reactions that occur. There is a window of temperatures that produce favorable reactions for the ideal cup characteristics. Temperature values outside of this window have a negative effect on quintessential cup quality. Even within the window values, different temperatures will change the character of the cup, giving the roaster the latitude to develop a personality or style desired, or to tame the rough signature of certain coffees while still optimizing relative quality. System Energy: At any given environment temperature, the amount of energy (BTU) and the roasting system's transfer efficiency will determine the rate at which the specific chemistrywilloccur. Higher levels of both energy andt ransfer efficiency will cause the reactions to progress more quickly. There is a window of reaction rates that will optimize cup quality. This is called the Best Reaction Ratio, or BRR.

Best Reaction Ratio (BRR)

The best cup characteristic are produced when the ratio of the degradation of trigonelline to the derivation of Nicotinic Acid remains linear. The control model of this reaction ratio is a time/temperature/energy relationship. The environment temperature (ET) establishes the pyrolysis region for the desired chemical reactions while the energy value (BTU) and system transfer efficiency (STE) determines the rate of reaction propagation and linearity of Nicotinic Acid derivation to degradation of trigonelline. Because green bean density varies dramatically, under any given ET / BTU / STE format, the reaction distribution will vary. It takes longer to obtain comparable uniformity for a higher density bean. Monitoring the bean temperature offers a good method of approximating the reaction distribution during this phase of the roasting. The ideal environmental temperature, ET, for best reaction ratio, BRR, is from-401-424 degrees F, with 405 degrees F as the default value. The BTU required is determined by the systems transfer efficiency, or ability to impart the energy to the charge mass.

Maximum Environment Temperature (MET)

Establishing the thermal environment protocol for the ideal roast is a balancing act. While it is desirable to maintain the BRR temperature and energy levels until the target reactions are achieved, the BRR temperature is well above the carmelization temperature of sucrose. Because many roasting systems exhibit thermal hysterysis using simple temperature regulating schemes, care must be taken not to allow the coffee mass to exotherm. Additionally, limiting the maximum environment temperature, MET, is also important. As previously mentioned, maintaining structural integrity of the cellulose matrix is of great importance. Lower temperatures will reduce surface evaporation of constituents minimizing the capillary action that draws constituents to the surface where they would be volatilized. Hydraulic action, a function of internal pressure which is directly related to bean temperature, is already at work. By limiting the maximum temperature, losses will be minimized and the essence of coffee retained. Consequently, the MET should not exceed 520 degrees F. This roasting system bases the MET value on the actual final bean, or drop temperature, which correlates to the degree of roast.

Translation

Many thermal and chemical reactions take place during baking: decarbonation, dehydration of quinic acid, subdivision, isomerization, polymerization, and complex sugar reactions (caramelization). The main components of the thermal reaction are monosaccharides and sucrose, chlorogenic acid, free amino acids, and fenugreek amide. Both aravinose and calactose in the polysaccharides were transferred, and the basic vulcanization included hydroxy acid decomposition. Carbohydrates are polymerized and decomposed at the same time, and depending on the degree of baking, 20-30% of the polysaccharides are broken down, releasing thermally unstable monosaccharides.

Sucrose: a disaccharide consisting of D-glucose and 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), and the accepted melting point is 370 degrees Fahrenheit (187.8 degrees Celsius). The melting point of degraded dried sucrose can be as low as 194 degrees Fahrenheit (90 degrees Celsius), and as it is dehydrated and concentrated, the sugar begins to split into glycoside conjugates. Between 338 and 392 degrees Fahrenheit (170 and 200 degrees Celsius), the caramelization reaction begins. It is at this point that water and carbon dioxide burst, and the resulting outgassing causes an explosion. These are chemical reactions that occur at about 356 degrees Fahrenheit (180 degrees Celsius), which is an exothermic reaction. It is very important that once the caramelization begins, the coffee should not release heat (heat), otherwise the coffee cup will taste like "baked". One possible explanation is that the release of heat from heated coffee beans breaks the long polymer chain and causes the broken long chain to connect to other ingredients. Sucrose and later converted ingredients, or caramelization, are determined by the presence of water, ammonia, and proteinatious substances. Heavy baking shows a higher degree of caramelization than light baking. The degree of caramelization is a good measure of baking with high resolution.

Cellulose: anhydrous long linear polymer (A Long Linear Polymer of Anhydroglucose Units)

Cellulose is the main fiber in the cell wall of coffee. This is local order (crystallization) and local disorder (amorphous / amorphous). The amorphous region is easily affected and easy to react, but the crystal region is closely packed and hydrogen-bonded, which is almost completely unaffected. Natural cellulose, or cellulose I, is converted into isomers cellulose III and cellulose IV when heated. The structure of coffee is a well-developed matrix, which improves the consistency of quality and contributes to the uniform spread of heat during baking. Cellulose exists in coffee in the form of embedded in lignocellulose (an amorphous matrix containing hemicellulose and cellulose-containing lignin), which form matrix unit walls (cell walls). Hemicellulase (hemicellusloses) is a polysaccharide composed of bifurcated sugar and uronic acid. 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 beans exceeds 536 degrees Fahrenheit (280 degrees Celsius), the cell wall is severely damaged. The actual temperature will change according to other factors. The second explosion associated with deep baking is the rupture of this matrix, which may be accompanied by volatilization of lignin and other aromatic hydrocarbons. Under controlled roasting conditions, the ambient temperature of beans should never exceed 536 degrees Fahrenheit (280 degrees Celsius). A wider safety line should limit the maximum ambient temperature to 520 degrees Fahrenheit (271.1 degrees Celsius). These temperature limits can minimize damage to the cell matrix, increase the complexity of performance in the cup, increase roasting yield and product shelf life cycle.

Fenugreek amide (Trigonelline): a nitrogen group (A Nitrogenous Base) found in coffee

Fenugreek amide is 100% soluble in water, so it will eventually appear in the cup. Fenugreek amide is the most important ingredient that produces excessive bitterness. About 85% of fenugreek amide degrades when the bean temperature is 445 degrees Fahrenheit (229.4 degrees Celsius). When the bean temperature is at this point, the beans are baked at a medium depth. There is more fenugreek amide for lighter baking, so it tastes bitter, 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 can set off each other to make the 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 378degrees Fahrenheit (192.2 degrees Celsius). The degradation of fenugreek amide is one of the key control indicators to determine the optimal reaction ratio.

Quinic acid: a member of the carboxylic acid group

The melting of pure crystals of quinic acid begins at 325 degrees Fahrenheit (162.8 degrees Celsius), much lower than the temperature in the baking environment. Quinic acid is water-soluble, slightly sour (not the bad taste of fermented beans) and sharp, giving more characteristics and complexity to the performance in the cup. Surprisingly, it also brings a clean it adds cleanness to the finish of the cup as well to the cup-tested aftertaste. It is a stable compound at baking temperature.

Nicotinic acid: a member of the carboxylic acid group

The melting of pure crystals of nicotinic acid begins at 457 degrees Fahrenheit (236.1 degrees Celsius). Natural nicotinic acid is bound to the structure of polysaccharide cellulose. Nicotinic acid is derived from soluble form during baking. Regardless of the degree of baking, high-grade niacin is always associated with good cup performance. Because it is 100% soluble, it will eventually appear in the cup. Niacin contributes to good flavor acidity and clean aftertaste (clean finish). Its derivative rate is a key control marker that can be used to determine the temperature of the optimal reaction rate, as well as the chemical transmission rate (chemistry propagation rates). In addition, the interaction of melted nicotinic acid with other components can significantly increase the brightness of deep-roasted coffee (shown 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, (baking in this window) will produce a good flavor reaction and produce the ideal performance in the cup. The temperature beyond this window will have a negative effect on the performance of the classic cup. Even if the temperature value is in the window, different temperatures will still change the characteristics of the cup, giving the baker space to develop a personal style or a desired style, or to tame the personality of a coarse mineral in a certain kind of coffee. at the same time, the relevant quality can still be controlled to the best.

System energy

At any given ambient temperature, the amount of energy (BTU) and the transmission efficiency of the baking system will determine the rate at which specific chemical changes occur. If the energy and transfer rate are high, the reaction will be faster. The reaction rate also has a window in which the quality of the cup can be optimized. This is called the optimal reaction rate, or BRR for short.

Optimal reaction rate (BRR)

The best cup characteristics are produced at a time when the ratio of fenugreek amide degradation to nicotinic acid derivation remains linear. The control model of the reaction rate is the relationship of time / temperature / energy. The ambient temperature (ET) established the high temperature decomposition zone of the desired chemical reaction, while the energy value (BTU) and system transfer efficiency (STE) determined the rate of reaction propagation and the linearity of the ratio of nicotinic acid derivation to fenugreek amide degradation. Because the density of mung beans varies greatly, the distribution of reactions will be different under any given ET / BTU / STE format. For high-density beans, it takes a long time to get comparable consistency. At this stage of baking, monitoring the temperature of beans is a good way to make the reaction distribution similar. The ideal ambient temperature, ET, to get the best reaction ratio, BRR, is from 401 to 424 degrees Fahrenheit (205 to 218 degrees Celsius), and 405 degrees Fahrenheit (207.2 degrees Celsius) is the default. The BTU required is determined by the transmission efficiency of the system, or the ability to transfer energy to the beans.

Maximum ambient temperature (MET)

Establishing a thermal environment protocol for ideal baking is a balance point. Although it is expected to maintain the BRR temperature and energy level until the target of the reaction is reached, the BRR temperature will be much higher than the caramelization temperature of sucrose. Because many baking systems use a simple temperature regulation mechanism, these systems show a thermal lag effect, so be careful not to let the coffee heat up. In addition, it is also important to limit the maximum ambient temperature, MET. As mentioned earlier, it is very important to maintain the structural integrity of the cellulose matrix. A lower temperature reduces the surface evaporation of the components, minimizing the capillary phenomenon that absorbs the ingredients to the surface and volatilizes them. Hydraulic pressure, an internal pressure directly related to bean temperature, is already at work. By limiting the maximum temperature, the loss is minimized and the essence of the coffee is retained. Therefore, MET should not exceed 520 degrees Fahrenheit (271.1 degrees Celsius). The baking system is based on the value of MET, the actual final bean, or the temperature of the next bean, which is related to the degree of baking.

Author: Carl Staub

Derived from the SCAA baking color classification system, developed by Agtron-SCAA 1995

The original text is from: http://www.sweetmarias.com/roast.carlstaub.html

Translation: Grant, http://51coffee.blogcn.com