STRUCTURE

A raw coffee bean’s structure is a three-dimensional, cellulose, or polysaccharide, matrix containing approximately a million cells. Coating the cellulose strands within that matrix are hundreds of chemicals that the roasting process will transform into the oils and soluble material that determine the brewed coffee’s flavor. Green coffee’s cellulose structure contributes half of its dry weight. The cellulose contributes little to coffee flavor but does trap some volatile compounds, which are responsible for aroma, and adds to brewed coffee’s viscosity, increasing its perceived body.

Raw coffee seeds (beans) are dense, a pale green, and consist of about one-half carbohydrate in various forms, and one-half a mixture of water, proteins, lipids, acids, and alkaloids (naturally occurring organic compounds that contain at least one nitrogen atom).

SUGARS

Sugars, dominated by sucrose, make up 6% - 9% of a green bean’s dry weight and provide sweetness in the cup. Sucrose also contributes to development of acidity, as the caramelization of sucrose during roasting yields acetic acid.

LIPIDS

Lipids, primarily triglycerides, make up approximately 16% of green coffee’s dry weight. Although lipids are not water soluble, brewed coffee contains some, especially when the brewing method uses either no filtration (like cupping) or a very porous filter (like metal filters/french press). Lipids in brewed coffee help retain aroma and contribute to the coffee’s mouthfeel. Higher lipid content is generally associated with better green coffee quality. Unfortunately, lipids also present challenges to quality, as they are vulnerable to oxidation and rancidity during storage of roasted beans.

ALKALOIDS: CAFFEINE & TRIGONELLINE

Two alkaloids, caffeine and trigonelline, each account for approximately 1% of green coffee’s dry weight and are responsible for much of coffee’s perceived bitterness and stimulating properties. Caffeine contributes approximately 10% of coffee’s bitterness and the majority of its stimulant effect. The coffee plant produces caffeine as a defense against insects. A coffee tree planted at a higher altitude generally produces less caffeine because of the lower risk of insect infestation or attack.

Trigonelline is perhaps the greatest contributor to coffee’s bitterness, yields many aromatic compounds, and degrades to pyridines and nicotinic acid during roasting. Nicotinic acid is also known as niacin, or Vitamin B ; a mere 7oz (200 grams) of brewed coffee, depending on level of roast, contains 20-80ml of niacin, which is likely responsible for coffee’s documented anti-cavity effect.

PROTEINS

Proteins and free amino acids make up 10% - 13% of green coffee by dry weight. Amino acids and reducing sugars in coffee beans interact during roasting in non-enzymatic browning reactions known as Maillard reactions. These reactions produce glycosylamines and melanoidins. that contribute to coffee’s bittersweet flavor, brown color, and roasted, savory aromas.

ORGANIC ACIDS

Organic acids, primarily chlorogenic acids (CGAs), constitute approximately 7% - 10% of green coffee’s dry mass. CGAs contribute to coffee’s perceived acidity, sourness, astringency, and bitterness. Robusta coffee’s higher CGA content is likely responsible for its significantly greater bitterness, aside from the fact that Robusta coffees tend to be roasted much more than our trend with Arabica. CGAs offer antioxidant benefits. Other organic acids in coffee include citric, quinic, caffeic, malic, and formic. The level of these acids varies between coffees, and each acid is responsible for specific cup characteristics that you may associate with other fruits; citric is responsible for orange, lemon, lime-like characteristics, malic is responsible for apple-like characteristics.

MOISTURE

Water should account for 10.5% - 11.5% of green coffee’s weight. If moisture content is too low, bean color is typically faded and the cup has notes of hay and straw. A roaster must apply heat cautiously to low-moisture beans, as they are likely to roast too fast. If moisture content is much higher than 12%, green coffee is prone to developing mold and may taste grassy in the cup. Water slows heat transfer within beans, and it requires extra heat input to evaporate. Roasting extra moist beans requires extra energy in some combination of added time and roasting power.

GAS AND AROMATICS

Volatile aromatic compounds provide coffee’s aroma. Green coffee contains more than 200 volatiles but offers little aroma. Roasting creates the vast majority of coffee’s aromatic compounds, and so far, researchers have identified 800 volatiles in roasted coffee.