A Bitter Cup (NY Times)

Victoria Roberts

A. Coffee is a complex chemical soup, and many of its chemicals, including some that produce astringency rather than bitterness, and even some acids, have been implicated in the perception of bitterness.

Bitterness also depends on variables including the coffee variety; how it is processed and roasted; the brewing method, temperature and time; and even the chemical content of the water.

Some degree of bitterness is desirable in coffee, according to the Coffee Research Institute, because it reduces the perception of acidity, for a more balanced flavor.

Some of the possible chemical culprits include quinic, chlorogenic, caffeic, citric, malic, lactic, pyruvic and acetic acids; 5-hydroxymethylfurfural; methyl furan; furfuryl mercaptan; trigonelline; pyrazine; thiazole; quinoline; phenylpyridine; and caffeine itself.

Studies reported by the institute suggest that perceived bitterness can be reduced by using hard or soft water, as opposed to distilled water; brewing at high temperatures, perhaps because more aromatic chemicals are released, canceling out the bitter ones; and using varieties other than robusta coffee, which has more caffeine and chlorogenic acid.

The institute also suggests using medium-roast coffee, which has a lower level of soluble solids; brewing using a drip system, which also cuts down the release of soluble solids; and perhaps using a coarser grind.

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