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THE CHEMISTRY OF COFFEE FLAVOR coninued fro page 97

But what are the basics of how these hundreds of chemical com-

pounds produce the wonderful experience of drinking fine coffee?

I asked Paul Songer, technical director for the Association of Coffee

Excellence and a consultant specializing in the sensory analysis of

coffee. The first thing is the old saw, The whole is more than the

sum of its parts. Many coffee chemicals are undesirable on theirown or in too great a concentration. Songer also points out that

chemistry is devoted to looking at individual chemicals and their

interactions, and he cautions that this alone cannot fully explain

coffee flavor. Even one class of chemicals, such as acids, cant fully

explain coffee flavor, he says. Having understood that, coffee is a

complex combination of acids, volatiles, oils and other lipids, salts,

nitrogenous substances (including caffeine), and carbohydrates.

By way of contrast, I wanted to know why truck-stop coffee, made

from low-quality robusta, old and mishandled, is still recogniz-

able as coffee. And what else does specialty coffee bring to this?

According to Songer, Though a lot of volatiles evaporate as coffee

sits, most of brewed coffees volatiles are contained in the oils.These are released in the mouth and perceived retronasally

that is, through the nose after the coffee is swallowed. Remaining

browned carbohydrates, acids, salts and especially chlorogenic acid

give us the impression that the vapid sour brew might have some

resemblance sensorially to coffee.

However, Songer says that as humans, we dont mind high con-

centrations of flavors in our foods and beverages if the flavors are

positively perceived. Making a robusta truck-stop coffee at high

concentrations would take the top of your tongue off and leave

unpleasant astringency and bitterness that might last for days,

while making a Cup of Excellence selection at double the strength

would give the impression of a damn strong cup, but not necessarily

unpleasant. It is the balance of the chemicals present that are

different, as well as the concentration in solution.

The chemistry of coffee flavor is really an interaction ofthe coffees chemical makeup with the physiology of thesenses. The sense of taste involves the four basic tastessalt, sweet, sour and bitterand new research shows that there are

receptors on the human tongue for other things, such as amino

acids, fats and glutamates (something flavor professionals call

umami after the Japanese word for a round, savory flavor found in

soy sauce, MSG, tomatoes and Parmesan cheese). Important tastes

in coffee include alkaloids, which provide its characteristic bitter

aspect, and tannins, which give an astringent feel and crisp delivery

to taste, but cannot be smelled. For a substance to be smelled, it

must be volatile (tending to evaporate) and oil-soluble (dissolves in

oil but not in water). So what actually dissolves in the water is the

tasted compounds, while the oil-soluble aromatics are suspended

in the coffee. While humans can taste only a handful of these

simple tastes, they can smell more than 10,000 distinct aromatics.

The combination of taste and aroma is called flavor.

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FRESH CUP MAGAZINE

THE ISSUE OF ACID

Paul Songer was eager to dig into the crucial aspects

of acid. Acidity is a complex issue, he says. What

cuppers identify as acidity is really only part of the

big picture. And these parts of the picture are indeed

acids, containing an H+ ion in combination with abalancing - ionic chemical or group of chemicals.

These join with water to form hydronium, H3O+,

which is perceived by certain taste sensors as acid or

sour. The issue is complex, but here are the highlights

according to Songer:

AromAtIC ACIDs: As their name implies, these can

be smelled as well as sensed as acid. They include lactic

acid and acetic acid, which is the main one and is the

chemical name for vinegar. Acetic acid is a product of

production: some is developed when the fruit is sepa-

rated from the seed, and some during roasting as the

result of sugar browning. The interesting thing aboutacetic is that how it is perceived has to do with its

concentration. A little bit adds to the pleasurable

nature of acidity. A little higher concentration and the

coffee tastes like over-ripe fruit or a bit grape-y/wine-y.

A little higher yet and its like onions. Still higher and it

is disagreeably sour, until finally it is a main contributor

(with other aromatics) to the defect known as ferment.

Some is always present, however.

the fruIt ACIDs: These are the ones that mainly

contribute to fine acidity and are the subject of most

discussions at the cupping table. Predominant is citric

acid, a fairly strong tasting acid, but fruit acids are alsomodified by others such as malic (also found in apples),

tartaric (also found in grapes) and others. An acid profile

is usually regarded more highly if there is a more complex

matrix of these acids present in a beverage. This sort is

usually more developed at high altitudes, which is why

high-altitude coffees tend to have the best acidity.

ChlorogenIC AnD quInIC group: Coffee has a

high concentration of chlorogenic acids of a number

of types. Upon roasting, these degenerate into cafeic

and quinic acids and phenols. One type, di-chlorogenic,

is mainly found in less ripe coffee, black beans and

immature beans, and it is perceived as astringent andgreenish. Chlorogenic itself is perceived as more bitter;

in the form of quinic, it is sour/bitter (think of the

quinine in tonic water). A little adds to the quality and

interest of the acids; too much is unpleasant.

InorgAnIC ACIDs: This includes phosphoric acid,

which definitely adds to the positive perception of

acidity. (Kenyas with high concentrations of phosphoric

acid are usually said to have fine acidity.) It is a strong

acid that acts in complex with the other acids and salts

to give a particularly pleasant and lingering note.continued on page 100


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THE CHEMISTRY OF COFFEE FLAVORconinued fro page 98

Taste, according to Songer, is the most consistent way we have

of evaluating our experience. While aromas also are important,

recent findings indicate that when we imbibe a food or beverage, it

is our experience of taste that our brain uses to set up our sensitivi-

ties to expected perception of certain aromas. We are capable of

sensing thousands of aromas (and other perceptions, such as thetemperature of a room were in), but we are not always conscious

of all these perceptions (though we can get better at this with prac-

ticethats what a good cupper does). The taste balance of fruit

acidity, sweetness, saltiness (potassium salts in the case of coffee),

bitterness, and their balance with one another, are mainly respon-

sible for our evaluation of coffee, says Songer.

When we perceive from a taste perspective a certain combination

of sourness and sweetness with which we are familiar, it may cause

us to be more sensitive to lemon or other citrus fruits. This phe-

nomenon is why one cupper will find nuts and chocolate aromas,

while another will find fruit and flowers.

Sweetness in coffee comes from sugars, most of which caramel-ize during roasting to produce a warm toastiness. The uncaramel-

ized sugars dont give a distinct sweetness, so the sweetness of

coffee is mainly the darker tone of caramel. This is complemented

by many aromatics that also provide caramel-like aromas.

Bitterness, though in America almost synonymous with an unpleas-

ant taste, is an important factor in the taste of coffee. Indeed, much

of the reason some drinkers add sugar to black coffee or espresso is

to balance the bitterness; but without the bitterness, the beverage

would be unrecognizable as coffee. In fact, adding any of the other

tastes has been found to reduce the sensation of bitterness, whether

sugar, salt or sour acid; just dont try this at home. Bitterness itself

helps balance the acidity in coffee. Aromatics can also balance bitter-

ness. This is part of the balance of tastes in coffee: The best taste is

found in the complementarity of the different factors.

Caffeine contributes a bitter taste to coffee, but it is only respon-

sible for about 10 percent of the overall bitterness, to which more

than 20 different compounds contribute. Other compounds related

to quinine give coffee an element of bitterness similar to that of tonic

water. Another important chemical component of coffee is niacin (in

coffee chemistry usually called by its chemical name, trigonelline).

Niacin is bitter, but roughly 85 percent of it is converted in roast-

ing to pyridines, which taste warm and roasty. The darker the roast,

the more this bitterness is turned to roast aroma. The main cause

of excessive bitterness is over-extraction, whether by brewing time,

fineness of grind, water quality or brewing method.

T here are other gustatory factors beyond the basic tastes,such as mouthfeel, astringency and even spiciness, whichare actually picked up by pain-sensation nerves in responseto the irritating, oily resin called capsicum. This last is not a factor

in coffee, though. (And if you do detect some while tasting a coffee,

count it as a fault!)

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THE CHEMISTRY OF COFFEE FLAVOR coninued fro page 100

Songer points out, Recent research points to the importance

of body and other issues of mouthfeel in the overall experience of

coffee drinking and enjoyment, especially in the case of espresso.

They are not purely physical phenomenon as once thought, but

involve a complex set of responses that include gustation (taste)

responses in order to form a general impression.

The feeling of astringency tells you that a compound is chemi-

cally reacting with your saliva, thinning it and making reacted

proteins fall onto the tongue. A little of this gives the coffee a

more fluid feel and helps the taste reach the tongue; too much

of it gives a rough, dried-out feeling to the tongue.

As in wine and tea, tannins play a role in coffees flavor.

According to Joseph Rivera, director of science and technol-

ogy for the SCAA, Tannins affect coffee in two ways: body and

astringency. What has more body, a sauvignon blanc or a cab-

ernet? The cabernet, due to a greater tannin content from the

grape skins and seeds, which also provides the red color. The

body of coffee depends greatly on the total tannin content and

concentration of dissolved short-chain carbohydrates. Perhaps

one of the most important tannins, or tannin-like compound, is

chlorogenic acid.

This raises the related and often misunderstood question of

acid. Altogether, about 50 important acids are found in coffee,

including the more familiar lactic (milk) acid, malic (apple) acid

and citric acid. How does this quality work? Is a chemical acid

tasted as sour? And is the desirable quality of acidity in coffee,

in fact, an acid?

Rivera teaches a workshop focusing on organic acids. The big

picture, according to him, is that, Although all acids are sour in

nature, some taste better than others. Of course, the key here

is moderation, as too much acidity will imbalance the coffee.

From a chemical point of view, it makes sense that coffees of

higher acidity taste better. A coffee with a higher acidity (i.e.,

lower pH) will always have more aroma, which in turn means

more flavor.

T hough the four basic tastes seem simpler than the com-plex aromatics, these tastes are generated by a wide arrayof chemical compounds, and it is their full and comple-mentary balance that gives the foundation to a rich flavor.

What really brings life to coffee as we know it, says Rivera,

is not so much the taste component, but rather what we pick up

from our olfactory senses.

Perhaps one of the most important aspects of coffee flavor

originates from the soil, Rivera adds. Why? Of the hundreds of

aromatic compounds found in coffee, they all contain sulfur as a

chief aromatic constituent, such as in the key coffee aromaticcompounds called mercaptans. Because volcanic soils have a

high concentration of sulfurous compounds, the coffees culti-

vated there tend to have a greater aroma content.

T he above aromatics give you the basic coffee aromaprofile, combining caramel, toastiness and the roastedflavor similar to other Maillard-reaction effects, likebread crust, seared steak and tobacco onions. In culinary sci-

ence, Maillard reactions are key to many cooking processes, and

they were even the source of some controversy when a recent

book on the science of cooking pointed out that caramelized

onions are not caramelized at all, but Maillard-ized.

Maillards, Songer explains, are the result of sugar joining

up with an amino acid and can smell like anything from a skunk

to fruits and flowers. In research, several studies point to mercap-

tans and other sulfur-based aromatics (mainly Maillard reactions)

as being most responsible for what we recognize as coffee.

One pyrazine, which gives an earthy aroma, is also a flavor

constituent in bell peppers. Phenols found in coffee aroma are

also an important element in the aroma of single-malt Scotch

whiskies, especially malts from Islay, in which phenolic is

a typical characteristic associated with their salty, spicy, sea-

weedy character. Diacetyl, which is produced by fermentation

bacteria during coffee processing, gives a rich, buttery aroma.

Coffee also contains the familiar compound vanillin, which

brings its delightful scent of vanilla to the brew. Still others

carry aroma elements described as sweet and potato-like, or

honey-like and fruity.

It is really the complexity of these factors that makes good coffee

so entrancing and gives such wonderful variety to different beans.

Smelling hundreds of pleasant aromas, some overlapping and oth-

ers complementing each other, is a feast for the senses and deeply

engaging for the brain.

AromAtICs

furAns are he os abundan class of aroaics

in coffee, and conribue carael aroas fro he

sugars broken down by he hea of roasing.

pyrAzInes are he nex os abundan, wih

roas-y, walnu-y or oasy aroas. they can be

selled even in sall aouns, and so conribue

uch o he aroa.

pyrroles give swee odors of carael or even

ushroos.

thIophens have a eay aroa fro maillard

reacions beween sulfurous aino acids and

sugars.

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