Acid citric (AC) is a type of acid used. CA is a critical intermediary in plant metabolism, like many other living species. The citric acid in green coffee is responsible for a large amount of the total acidity and, as a result, the development of edge.
CA peaks at light to medium roasts (Medium) and then rapidly decreases as the roast level increases. In the final stages of the roasting process, a typical medium roast will lose around half of its initial CA concentration and steadily lose it.
Citric has a robust sour flavor akin to what we would find in unripe fruit. Although pure CA is commonly employed as a food ingredient, too much of it is a symptom of poor processing.
Because unripe (green) coffee cherries contain significant levels of CA, manufacturers must select only the ripest cherries, especially those destined for specialty coffee.
However, the CA content decreases as the fruit ages while the sugar rises. Kenyan coffee contains lower citric acid contents than Central American coffees, implying a poorer plant metabolism.