Quinic Acid |
Quinic acid along with citric and malic represent a significant portion of total acid content in green coffee4. During roasting quinic acid progressively increases as the level of chlorogenic acid decreases, suggesting that its formation results from the cleavage of chlorogenic acid. Quinic acid concentrations reach a maximum at French roasts then progressively decrease as roasting progresses5. Actual temperature figures of when this ocurs have yet to be published. For now published concentrations on quinic acid in both green and roasted form are summarized in Table 1 below.
Further thermal degradation of quinic acid results in the formation of phenol, catechol, hydroquinone, pyrogallol and several diphenols which are believed to be important coffee aroma precursors3. Quinic acid has also been associated with an increase in perceived acidity as the coffee infusions are left standing at elevated temperatures. This effect is best illustrated if coffee is left stored on heating plates at temperatures above 80oC. According to Parliment, it is during these evelvated temperarures that quinide, which is typically not sour, slowly hydrolyzes back into quinic acid and thus increasing sourness4. The same effect is seen during cupping as coffee samples sit and an increase in perceived acidity is observed. References:
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