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.