WHAT DETERMINES THE COLOR OF BREWED COFFEE?

dominant homozygous “XcXc” gives the red color to the cherries. These genes lead the fruit’s

metabolism to produce red-colored substances like anthocyanins (cyanine, pelogonin, and peonin). In

yellow(ish) coffee fruits the genes are homozygous recessive “xcxc”, and the predominance of

leucoanthocyanins neutralizes anthocyanins, which allows the production of yellow flavones such as

luteolin and apegenine.

Anthocyanins belong to a parent class of molecules called flavonoids synthesized via

the phenylpropanoid pathway. They are phenolic compounds which can be found throughout the plant kingdom; occur in all tissues of higher plants, including leaves, stems, roots, flowers, and fruits. They are

odorless and moderately astringent. We used to originally and incorrectly classify phenolic compounds

as tannins, according to Lingle (2011), although there are tannins in coffee but they are not the main

ones. Condensed tannins are the main phenolic compounds in coffee pulp and skin, however, in the

seed, phenolic compounds are present predominantly as a family of esters formed between certain

hydroxycinnamic acids and quinic acid, collectively known as chlorogenic acids (CGA) (Clifford, 1985).

Chlorogenic acids (CGA) and related compounds are the main components of the phenolic fraction of

green coffee beans, reaching levels up to 14 % (dry matter basis, depending on species and varieties). It

is worth mentioning that basically chlorogenic acid is a pseudo tannin, which is a low molecular weight

compound associated with other compounds. So talking about tannins in coffee (astringency, color

absorbance, etc.) might not be wrong, but also it’s not accurate. According to Bekedam et

al. (2008), incorporation of chlorogenic acid plays an important role in coffee brew melanoidins

formation.

I believe next to chlorogenic acids, anthocyanins also could play a significant role in the formation of

coffee brew melanoidins. To my knowledge, there is no study to prove this argument and I’m not a

biochemist to say that. Yet the answer might lie in the processing method: we already know that there

are anthocyanins in coffee pulp and skin. And empirically we observe the color differences between

different processing methods (say wet vs. dry). In a study in 2007, Prata investigated fresh coffee husks,

comprised of outer skin and pulp, as potential sources of anthocyanins for applications as natural food

colorants.

“In the wet process, the coffee husks are removed prior to drying, while still fresh, and their color is

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rapidly degraded by the action of enzymes (peroxidases and polyphenoloxidases) liberated by the

damaged cells of the outer skin and pulp during the de-hulling process, or by other oxidizing agents,

such as oxygen. Thus, large amounts of natural colorants are wasted in this process (Prata, 2007).”

Given that these pigments (anthocyanins) are water soluble, could it be the reason why wet-processed

coffees tend to have more clarity and be lighter in color? While dry-processed coffees are darker in

color with less clarity? To me, it’s like as if

phenolic compounds or to be more specific in my argument,

anthocyanins are bleached in the wet process and somehow leach/percolate in the dry process.

Therefore, the amount (concentration) present at the time of the reactions during roasting

could lead to creating low to high molecular weight melanoidins.