What is Chlorogenic Acid and What is Its Relationship with Coffee Roasting? The Acidity in Coffee Comes from Chlorogenic Acid

FrontStreet Coffee: What Is Chlorogenic Acid and Its Relationship with Roasting?

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Chlorogenic acid forms through an esterification reaction between quinic acid and caffeic acid, a dehydration condensation. It is a reversible reaction, which means chlorogenic acid can hydrolyze when exposed to water, breaking back down into quinic acid and caffeic acid. Because hydrolysis is endothermic, the heat of roasting drives that decomposition forward.

Chlorogenic acid is the most abundant organic acid in green coffee and the main culprit behind the sharp, astringent bitterness some drinkers dislike. Fortunately, it is broken down during roasting. More importantly, the extent of that breakdown is inversely proportional to roasting speed, meaning the interval between first crack and dropping the beans before second crack. A faster roast leaves more residual chlorogenic acid, while a slower roast leaves less. This explains why fast-roasted beans taste sharper and more acidic, while slow-roasted beans come across as smoother.

The Relationship Between Roasting and Quality Acids

Alongside the undesirable chlorogenic acid, green beans also contain many desirable acids, most importantly citric acid, malic acid, acetic acid, phosphoric acid, and quinic acid. Other organic acids are also created during roasting as carbohydrates break down. To date, as many as thirty-four different organic acids have been identified, fifteen of which are volatile.

As a rule, quality acids such as citric, malic, phosphoric, and acetic acid reach their peak concentration during medium roasting and decline as the roast gets darker.

Organic acids have a major influence on coffee flavor. Interestingly, the pleasant, lively fruity acidity of a light roast is the combined expression of more than thirty different organic acids. Let any single acid become too dominant, however, and the cup turns unpleasant.

FrontStreet Coffee Recommendation

If the sharp edge of chlorogenic acid is not for you, a medium roast is the sweet spot, where the harsh acids fall away while the desirable ones are still at their peak. The FrontStreet Brazil Queen Estate is a fine example: a yellow Bourbon from the world's largest coffee producer, medium roasted to a mellow, sweet cup of creamy peanut, chocolate, toasted bread, and sugarcane, and versatile enough for pour-over, moka pot, or espresso. For something sweeter and more fruit-forward, the FrontStreet Strawberry Candy blend marries a Costa Rican honey-processed coffee with a washed Panamanian Geisha at a medium roast, delivering orange-blossom honey depth and rounded sweetness that shines in cold brew, pour-over, or espresso. If balance is what you are after, the FrontStreet Jamaica Blue Mountain No. 1, a Typica medium roasted to blend acidity, bitterness, sweetness, and body into one elegant whole, offers chocolate, roasted nut, cream, and caramel in every sip.