We say time and again that the term "acidity" is used as a descriptor of positive attributes in coffee. Convincing folks that acidity is a positive characteristic and that we're not talking about the kind of acidity that makes a stomach sour is one of the core dilemas of of the purveyor of fine coffees. Acidity, the good kind, is responsible for a number of characteristics in coffee including many of those fruit notes. Knowing a little bit about which specific acids are responsible for certain fruit-like flavors can prove to be really helpful for learning how to identify these flavors, help you identify the coffees that you're really going to be the most happy with, and how to roast and store a coffee in order to promote or diminish specific characteristics. So here's a quick little primer in just a few of the acids found in coffee and what flavors they lead to.
- Citric Acid: Found in high grown arabica coffees, these acids lead to citrus flavors like orange and lemon or sometimes grapefruit in a coffee. Some research shows that citric acid is responsible for most of the acid flavors in coffee.
- Malic Acid: This can provide more of an apple or pear-like flavor to a coffee, sweet and crisp, but can also have stone fruit properties.
- Phosporic Acid: Not an organic acid, and can really push sweetness in a coffee. Tropical fruit flavors like grapefruit or mango are generally attributed to phosporic acid
- Acetic Acid: This is the main component of vinegar, so this can be an off flavor at higher levels. At lower levels in can have a pleasant sharpness or lime-like flavors.
- Tartaric: Tartaric acids are common in grapes and can lead to some winey or grape-like notes in a coffee, but can also be sour in higher levels.
- Quinic Acid: These are the bad guys, and these are indeed responsible for the sour stomach. Quinic acids increase in production the more and more the coffee degrades. Dark roasted coffees are hight in this while low in other flavor contributing acids, and also stale coffees, either coffees that were roasted a good while ago or that were brewed a long time ago (especially if left on a hot plate).
- Chlorogenic Acid: Responsible for a good deal of percieved acidity in the cup. For a long time it was simply said that roast level was responsible for the breaking down of some of these acids, but more accurately it is exposure time to the heat during the roasting. Prolonged exposure time can result in a reduced perception of acidity even if the final roast level is fairly light.