What it Was Was Clues, Part II ...
... Pulling Shots, Culling Current Chemistry for Clues to Cup By: Better Coffee Through Chemistry?Today il Professore seems to be in top form as he pulls a shot of another blend: "Here, my young friend is another epiphany, a blend that is a twist on Gimme's Leftist--searching for clues to sweetness. I am about to give you an intense dose, both in the shot and in my notes to follow of the chemistry of coffee to show that inherent and developed chemical constituents can be identified, leading to discovery of sweetness in the cup."
I drink it in; the fruitiness to sweet caramel is ascending, sour and bitter are passed by. I bet on an added slice of an Ethiopianin this version. "In this case, you are right", says the Professore, "and now I continue to show you a path to sweetness through chemistry, in this case identified as supplemental sacharrides, namely fructose, glucose. But read it yourself":
In PART I,
the contention blossomed that sweet, caramel, and syrup can be
developed, even increased, by purposeful roast technology, machine,
technique, and chemistry, coupled to an evaluation by espresso shots.
Now it's time to dive into that organic chemistry.
Roast techniques are determined by sought-after roast outcomes, which in turn are driven by roast chemistry. Sivetz and Foote, Coffee Processing Technology (1963), Sivetz and Desrosier, Coffee Technology (1979), Rothfos, Coffee Consumption (1986). Roast chemistry is a massive does of detail. A hefty compilation of developments in the chemistry of coffee, Clarke and Vitzhum (ed.), COFFEE, Recent Developments (2001), puts the chemistry within reach for tentative answers about developing sweetness and diminishing acidity, at least in the trial and error sense. The complexity of this chemical array is almost confounding, but there are groupings that are familiar, starting with coffee's non-volatile parts.
Non-volatile Compounds: Taste, Texture, Body
The non-volatiles may be the taste part of the coffee chemistry. Generally speaking they are sugars from simple to very complex, acids, and proteins.
Sugars
The mono-saccharides of green coffee are sucrose. Sucrose in Arabica varies from 6.25% to 8.45% and is much lower in robusta, from 0.9% to 4.85%. Among three origins of distinction, sugars, mono- and disaccharide (as percent of dry weight) are these:
The differences in composition of simple sugars are remarkable. Kenya, with its refined acidity (according to the lore of cuppers) rates high, possibly because of its relatively high sucrose, and that carries over to Colombia. Winey fruitiness may be the predominance of fructose-glucose in Ethiopian, nearly absent in Kenyan and Colombian.
Sucrose degrades to nearly nothing on roasting: for light roast to 3% and for dark roast to 1%. The roasting process dehydrates sucrose into glucose and fructose. These are reducing sugars that degrade even more rapidly than sucrose, so they too disappear into the roast outcome. There are three primary reactions from roasting sugars:
1. Acids for the front-end, sharp notes
The derivation of acids on top of existing acids is one. In roast coffee, sucrose is the chief source of derived acids. The major acids of roasting are formic, acetic, glycolic, and lactic. Acids from carbohydrates are higher in arabicas (with higher sucrose content of 70-80 g/kg) than in robustas (with 30-40g/kg).
The derived acids are dependent on the degree of roast. Development increases quickly during early weight loss, peaks at the mid-point, and decreases in a nearly perfect bell curve.
Acetic and formic acid are formed up to 240 degrees C (464 F) and then decrease; both are highly volatile. Lactic and glycolic acids increase beyond 240 degrees until 280 degrees (536 F). These seemingly high temperatures could be the result of stating transient environmental or fuel temperatures rather than relative bean temperatures.
During roasting there is a drop in pH from 5.7-6.0 to 4.9-5.5. In general, arabicas have a pH of 4.85-5.15 in the brew and robustas have a range of 5.25-5.40. Citric acid is the highest contributor to perceived acidity; chlorogenic and quinic acids are less so.
2. Dry Distillation for Browns, Cross-Polymers
Second, dehydration produces both caramelization and complex compounds, such as variants of furfural; these become volatile, or react to further polymerize.
3. Maillard Makes Melanoidins
Third, saccharides interact with protein to produce Maillard reaction products bringing long-chain polymers (melanoidins) that contribute color or which become low molecular weight components for both cup flavor and aroma. This brown complex is decisive because it can be as much as 30% of the brew solubles.
Though melanoidin is accorded such a large role in color, taste, and feel, interestingly no reference is included in this detailed material about the sensory attributes of a melanoidin by itself.
There are three dominant types of polysaccharides. All are polymers, one of which is cellulose. The cellulose of arabica contains 6.7% to 7.8% glucose and of robusta, 7.8% to 8.7%. Cell walls are thick and make for hardness of the greens; the walls survive roasting. These polysaccharides are strongly linked and remain intact throughout the roast with only slight degradation. The polysaccharides that are not converted remain fiber in the roast and cup, and are not digestible by coffee drinkers. But as for good news, there is evidence that the undigested fiber can lower colon cancer risk.
Inherent Acids: From Sour, Sharp, to Body
Sour and Sharp
In green coffee, the integral acids constitute about 11% of weight (and 6% of roasted weight). It is of dramatic, dynamic interest that wet processed coffees are higher in acid than naturals.
The major acids in greens are chlorogenic, citric, quinic, and malic. Chlorogenic acid is of the highest concentration. Citric acid is next. Kenya is lower in each of these acids, higher in malic.
Chlorogenic acid roasts to produce added quinic acid and lactones. These reach maximums in medium roasts. Citric and malic acids decrease in roasting. Robustas are higher in chlorogenic acid than arabicas and notable for the appearance of phosphoric acid. Since robustas contain more chlorogenics, the quinic acid content rises faster in roasting robusta. By the way, anti-oxidative activity is strongly associated with coffee's chlorogenics and roasted derivatives. Highest correlations were found in medium roasts, an interesting coincidence and another plus for mid-range roasting.
Body
Fatty acids are components of lipids, the coffee oils and waxes. Most oils are located in the fruity body of the bean; coffee wax is in the outer layer. These are the diterpenes, sterols, and tocopherols of roasted coffee. They are barely soluble, and may therefore account for formation of body and texture.
Proteins Link to Each: Bitter Aftertaste
Bitter taste is chemically associated to extended roasting, with proteins playing a structural role. Protein is an important contributor to Maillard reaction-melanoidin formation as are carbohydrates and chlorogenic acids. Brewed coffee is a mixture of sugars and derived melanoidins that became complex co-polymers. The resulting phenolic-melanoidin complex is degraded chlorogenics that start the roast process by binding with protein and sugars. Yet a significant portion of chlorogenics acid remains in the roast.
The decomposition of lactones and quinic acid at higher roast temperatures results in similar increased bitterness. Caffeine itself is a bitter element but only accounts for 10% to 30% of bitter taste.
Le Nez: the Volatiles from 800 to 28
As many as 800 volatile compounds have been identified in the roast through high-resolution gas chromatography and mass spectrometry. The more intense work has been the shortening of this list into the actual components of aroma, as we perceive them, which has been a combination of chemistry and sensory work. An initial spectrum analysis of the more potent volatiles resulted in a supremely complex list of components. Further concentration and sensory analysis produced a list of 28, which has been categorized by tasters into recognizable groups, even though the chemical names are rare, if not daunting, in complexity. Take, for instance "sweetish-caramel", containing 2,3- Pentanedione or 2-Methlybutanal, or go to "smoky/phenolic" for 4-Ethylguaiacol.
Though hardly recognized by their individual chemical tags, the headings are familiar and support the aromatic groups of key essences in the LE NEZ DU CAFE set of aromatics by Jean Lenoir, remarkably comparable to this latest chemical grouping. For example, the chemical group "toasty" includes the LE NEZ caramel, maple syrup, malt, chocolate, and farther down the list, smoke.
Light Roasts and Green Peas
Pyrazines in green coffee produce the odor of fresh green peas. The odor occurs in very light roasts, which are bright, acidic. The pyrazines are sensed as herbiness, hay, sometimes flowery notes, yet greenish, verging on underdeveloped. But be prepared to bear down in roasting, for these pyrazines are one of the hardiest, heaviest scents. "The smell is so strong that just a few drops could be detected in an Olympic-sized swimming pool." Lenoir, 20
Middle Range Masking
In tests where potent odorants in roasted coffee were selectively omitted, the absence of very few of the pyrazines was readily noticeable. The conclusion is that the overall power of "green peas" is masked or bridged by the development of other aromas as the roast progresses. Otherwise, green peas would predominate.
This sort of selective omission testing also showed that only a few of the total odorants of roasted coffee register with us as aroma. The sense of smell is either rather limited or somewhat specific in its sorting from the known 800 to the perceivable.
From roast to ground coffee to brew, the aroma profile changes with caramel, buttery, and phenolic scents becoming more intense. The components of the profile have not changed but extraction by hot water has modified the concentration of them. For example, the flowery damascenone (associated with the scent of damascene rose, one of the most expensive odorants) is reduced by 75%. This may explain why flowery, jasmine aromatics are perceived in dry grounds before cupping, but disappear when the crust is broken.
The Maillard reaction, which colors roasted coffee, also degrades saccharides into volatile compounds, linking acids and proteins to become precursors for odorants of the sweet, caramel, and earthy groups. Sweetish/caramel and green peas are more prominent in arabicas. But mustiness is a particular volatile odorant belonging to robusta, showing itself vigorously in mid-range
Not to be left unmentioned is the phantom Strecker degradation of amino compounds into very complex aldehydes. The aldehydes may be related to the group of spicy, fruity notes, another associative aroma set that becomes apparent in mid-range.
The Dark Side: Phenols and Furfurals
A higher concentration of phenols in robustas accounts for earthier, smoky notes Roasting dark increases the earthy, smoky and oily notes even of arabicas. If it goes dark-dark, the furfurals and phenols increase by as much as 82%!
The Trigonelline Tag
Less understood is the role of the decline in trigonelline connected to the arrival of nicotinic acid (known to us mortals as niacin) during roasting. The intersection of T and N is said to mark mid-range development of significant character. Trigonelline and caffeine are associated with hefty bitterness. Both survive through the roast but to different degrees. As trigonelline disappears, sweetness increases. Nicotinic acid's rise may relate to T's descent. Staub, Agtron Roasting System 1995 (unpublished). Into mid-range, trigonelline starts degradation at 378 degrees F to 85%, melting from crystalline form at 424 degrees F. Going to the dark side, at 457 degrees F, nicotinic acid melts from crystalline form and contributes to the intensity of dark roasts.
Hence, concludes il Professore, there are many indicators of complexity and subtlety set out in mid-range, character, sweetness and resounding, astounding aromatics; and so, he finishes that for next time, the idea is "staging" is where it all is.
The Professore turns to pull another shot of the latest expression, the complex of Leftist-Sidamo, sips contentedly. Ciao, il Professore.
Roast techniques are determined by sought-after roast outcomes, which in turn are driven by roast chemistry. Sivetz and Foote, Coffee Processing Technology (1963), Sivetz and Desrosier, Coffee Technology (1979), Rothfos, Coffee Consumption (1986). Roast chemistry is a massive does of detail. A hefty compilation of developments in the chemistry of coffee, Clarke and Vitzhum (ed.), COFFEE, Recent Developments (2001), puts the chemistry within reach for tentative answers about developing sweetness and diminishing acidity, at least in the trial and error sense. The complexity of this chemical array is almost confounding, but there are groupings that are familiar, starting with coffee's non-volatile parts.
Non-volatile Compounds: Taste, Texture, Body
The non-volatiles may be the taste part of the coffee chemistry. Generally speaking they are sugars from simple to very complex, acids, and proteins.
Sugars
The mono-saccharides of green coffee are sucrose. Sucrose in Arabica varies from 6.25% to 8.45% and is much lower in robusta, from 0.9% to 4.85%. Among three origins of distinction, sugars, mono- and disaccharide (as percent of dry weight) are these:
| Sucrose | Fructose | Glucose | |
| Colombia | 8.20 | 0.15 | <0.01 |
| Kenya | 8.45 | 0.02 | <0.01 |
| Ethiopia | 6.30 | 0.40 | 0.40 |
The differences in composition of simple sugars are remarkable. Kenya, with its refined acidity (according to the lore of cuppers) rates high, possibly because of its relatively high sucrose, and that carries over to Colombia. Winey fruitiness may be the predominance of fructose-glucose in Ethiopian, nearly absent in Kenyan and Colombian.
Sucrose degrades to nearly nothing on roasting: for light roast to 3% and for dark roast to 1%. The roasting process dehydrates sucrose into glucose and fructose. These are reducing sugars that degrade even more rapidly than sucrose, so they too disappear into the roast outcome. There are three primary reactions from roasting sugars:
1. Acids for the front-end, sharp notes
The derivation of acids on top of existing acids is one. In roast coffee, sucrose is the chief source of derived acids. The major acids of roasting are formic, acetic, glycolic, and lactic. Acids from carbohydrates are higher in arabicas (with higher sucrose content of 70-80 g/kg) than in robustas (with 30-40g/kg).
The derived acids are dependent on the degree of roast. Development increases quickly during early weight loss, peaks at the mid-point, and decreases in a nearly perfect bell curve.
Acetic and formic acid are formed up to 240 degrees C (464 F) and then decrease; both are highly volatile. Lactic and glycolic acids increase beyond 240 degrees until 280 degrees (536 F). These seemingly high temperatures could be the result of stating transient environmental or fuel temperatures rather than relative bean temperatures.
During roasting there is a drop in pH from 5.7-6.0 to 4.9-5.5. In general, arabicas have a pH of 4.85-5.15 in the brew and robustas have a range of 5.25-5.40. Citric acid is the highest contributor to perceived acidity; chlorogenic and quinic acids are less so.
2. Dry Distillation for Browns, Cross-Polymers
Second, dehydration produces both caramelization and complex compounds, such as variants of furfural; these become volatile, or react to further polymerize.
3. Maillard Makes Melanoidins
Third, saccharides interact with protein to produce Maillard reaction products bringing long-chain polymers (melanoidins) that contribute color or which become low molecular weight components for both cup flavor and aroma. This brown complex is decisive because it can be as much as 30% of the brew solubles.
Though melanoidin is accorded such a large role in color, taste, and feel, interestingly no reference is included in this detailed material about the sensory attributes of a melanoidin by itself.
There are three dominant types of polysaccharides. All are polymers, one of which is cellulose. The cellulose of arabica contains 6.7% to 7.8% glucose and of robusta, 7.8% to 8.7%. Cell walls are thick and make for hardness of the greens; the walls survive roasting. These polysaccharides are strongly linked and remain intact throughout the roast with only slight degradation. The polysaccharides that are not converted remain fiber in the roast and cup, and are not digestible by coffee drinkers. But as for good news, there is evidence that the undigested fiber can lower colon cancer risk.
Inherent Acids: From Sour, Sharp, to Body
Sour and Sharp
In green coffee, the integral acids constitute about 11% of weight (and 6% of roasted weight). It is of dramatic, dynamic interest that wet processed coffees are higher in acid than naturals.
The major acids in greens are chlorogenic, citric, quinic, and malic. Chlorogenic acid is of the highest concentration. Citric acid is next. Kenya is lower in each of these acids, higher in malic.
Chlorogenic acid roasts to produce added quinic acid and lactones. These reach maximums in medium roasts. Citric and malic acids decrease in roasting. Robustas are higher in chlorogenic acid than arabicas and notable for the appearance of phosphoric acid. Since robustas contain more chlorogenics, the quinic acid content rises faster in roasting robusta. By the way, anti-oxidative activity is strongly associated with coffee's chlorogenics and roasted derivatives. Highest correlations were found in medium roasts, an interesting coincidence and another plus for mid-range roasting.
Body
Fatty acids are components of lipids, the coffee oils and waxes. Most oils are located in the fruity body of the bean; coffee wax is in the outer layer. These are the diterpenes, sterols, and tocopherols of roasted coffee. They are barely soluble, and may therefore account for formation of body and texture.
Proteins Link to Each: Bitter Aftertaste
Bitter taste is chemically associated to extended roasting, with proteins playing a structural role. Protein is an important contributor to Maillard reaction-melanoidin formation as are carbohydrates and chlorogenic acids. Brewed coffee is a mixture of sugars and derived melanoidins that became complex co-polymers. The resulting phenolic-melanoidin complex is degraded chlorogenics that start the roast process by binding with protein and sugars. Yet a significant portion of chlorogenics acid remains in the roast.
The decomposition of lactones and quinic acid at higher roast temperatures results in similar increased bitterness. Caffeine itself is a bitter element but only accounts for 10% to 30% of bitter taste.
Le Nez: the Volatiles from 800 to 28
As many as 800 volatile compounds have been identified in the roast through high-resolution gas chromatography and mass spectrometry. The more intense work has been the shortening of this list into the actual components of aroma, as we perceive them, which has been a combination of chemistry and sensory work. An initial spectrum analysis of the more potent volatiles resulted in a supremely complex list of components. Further concentration and sensory analysis produced a list of 28, which has been categorized by tasters into recognizable groups, even though the chemical names are rare, if not daunting, in complexity. Take, for instance "sweetish-caramel", containing 2,3- Pentanedione or 2-Methlybutanal, or go to "smoky/phenolic" for 4-Ethylguaiacol.
Though hardly recognized by their individual chemical tags, the headings are familiar and support the aromatic groups of key essences in the LE NEZ DU CAFE set of aromatics by Jean Lenoir, remarkably comparable to this latest chemical grouping. For example, the chemical group "toasty" includes the LE NEZ caramel, maple syrup, malt, chocolate, and farther down the list, smoke.
Light Roasts and Green Peas
Pyrazines in green coffee produce the odor of fresh green peas. The odor occurs in very light roasts, which are bright, acidic. The pyrazines are sensed as herbiness, hay, sometimes flowery notes, yet greenish, verging on underdeveloped. But be prepared to bear down in roasting, for these pyrazines are one of the hardiest, heaviest scents. "The smell is so strong that just a few drops could be detected in an Olympic-sized swimming pool." Lenoir, 20
Middle Range Masking
In tests where potent odorants in roasted coffee were selectively omitted, the absence of very few of the pyrazines was readily noticeable. The conclusion is that the overall power of "green peas" is masked or bridged by the development of other aromas as the roast progresses. Otherwise, green peas would predominate.
This sort of selective omission testing also showed that only a few of the total odorants of roasted coffee register with us as aroma. The sense of smell is either rather limited or somewhat specific in its sorting from the known 800 to the perceivable.
From roast to ground coffee to brew, the aroma profile changes with caramel, buttery, and phenolic scents becoming more intense. The components of the profile have not changed but extraction by hot water has modified the concentration of them. For example, the flowery damascenone (associated with the scent of damascene rose, one of the most expensive odorants) is reduced by 75%. This may explain why flowery, jasmine aromatics are perceived in dry grounds before cupping, but disappear when the crust is broken.
The Maillard reaction, which colors roasted coffee, also degrades saccharides into volatile compounds, linking acids and proteins to become precursors for odorants of the sweet, caramel, and earthy groups. Sweetish/caramel and green peas are more prominent in arabicas. But mustiness is a particular volatile odorant belonging to robusta, showing itself vigorously in mid-range
Not to be left unmentioned is the phantom Strecker degradation of amino compounds into very complex aldehydes. The aldehydes may be related to the group of spicy, fruity notes, another associative aroma set that becomes apparent in mid-range.
The Dark Side: Phenols and Furfurals
A higher concentration of phenols in robustas accounts for earthier, smoky notes Roasting dark increases the earthy, smoky and oily notes even of arabicas. If it goes dark-dark, the furfurals and phenols increase by as much as 82%!
The Trigonelline Tag
Less understood is the role of the decline in trigonelline connected to the arrival of nicotinic acid (known to us mortals as niacin) during roasting. The intersection of T and N is said to mark mid-range development of significant character. Trigonelline and caffeine are associated with hefty bitterness. Both survive through the roast but to different degrees. As trigonelline disappears, sweetness increases. Nicotinic acid's rise may relate to T's descent. Staub, Agtron Roasting System 1995 (unpublished). Into mid-range, trigonelline starts degradation at 378 degrees F to 85%, melting from crystalline form at 424 degrees F. Going to the dark side, at 457 degrees F, nicotinic acid melts from crystalline form and contributes to the intensity of dark roasts.
Hence, concludes il Professore, there are many indicators of complexity and subtlety set out in mid-range, character, sweetness and resounding, astounding aromatics; and so, he finishes that for next time, the idea is "staging" is where it all is.
The Professore turns to pull another shot of the latest expression, the complex of Leftist-Sidamo, sips contentedly. Ciao, il Professore.
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Gabe May 22, 2009 – 7:24 AM
no wonder I got a C in chemistry! I totally can't hack it. thank god I love coffee!
Lance Fancy Pants May 22, 2009 – 10:36 AM
Fascinating, John. I hope to someday understand it fully, but it lays the groundwork for further exploration. Thanks.