Coffee Chemistry and Aroma

I find Coffee Chemistry and Coffee Aroma to be a good introduction to what it is about coffee that so intrigues us.

Coffee has taste, aroma, and body or mouthfeel. Body and mouthfeel are a separate (and extremely important) subject, while taste plus aroma equal flavor.

But taste per se is just a combination of sweet, salty, sour, and bitter (and, some say, umami, which accounts for the savory taste of meat and other foods). What distinguishes coffee's unique flavor is due to volatile aromatic compounds that waft into the nose either frontwise, through the nostrils, or retronasally, from the throat up into the back of the nasal passages.

The volatile aromatics we so enjoy come from the coffee bean after it is roasted, which in turn are developed during the roasting process from compounds present in the green, unroasted bean. The number of aromatic compounds in coffee is well over 800!

It is worth noting that, according to Start and Run a Coffee Bar by Tom Matzen and Marybeth Harrison, p. 134, coffee beans have "up to 450 flavor characteristics our senses can detect (by comparison, red wine has only 150), including floral, sweet, mellow, tart, sour, wild, woody, and buttery."

"The longer the bean is roasted, the more characteristics are burned off," the authors go on to say.

If there are 800+ compounds and only 450-or-so flavor characteristics, what can we say about the other roughly 350 compounds? One possibility is that they are not present in sufficient concentrations to cross the "odor threshold" of detectability. The article says, "It is probable that a relatively small group of compounds that share both a high concentration and a low odor threshold make up the fragrance we know as coffee aroma."

Well, possibly the "relatively small group," or so I'd speculate, numbers in the range of 450. Still, there are, the article says, certain aroma descriptors that predominate. Each is associated with a certain chemical substance the article mentions, but I'll just list the descriptors themselves:

• honey-like, fruity
• roasty (coffee)
• catty[!], roasty
• amine-like [whatever that means!]
• earthy
• [a compound that has no descriptor given]
• phenolic, spicy
• buttery
• spicy
• buttery
• potato-like, sweet
• earthy, roasty
• vanilla
• caramel-like
• earthy, roasty
• earthy, roasty
• seasoning-like
• spicy
• seasoning-like

(Notice that some descriptors go with more than one compound.)

Another important factor in coffee enjoyment is its "acidity, " covered in this companion article.