Coffee often gets branded as an acidic drink, but in fact, coffee comes in at around a five on the pH scale, which is actually less acidic than drinks like beer, orange juice, and even soda.
So, when we talk about acid and coffee, most often, we are not actually talking about the pH level of the drink. Here's what we are talking about.
Acid vs. Acidity
Acidity is one of the key components of how a coffee tastes. The word can be a little confusing, however, as usually when we are referring to food, acidic isn't usually a desirable quality. In fact, hear the word "acid" and you almost immediately think of a food or drink that's going to be sour in your mouth and hard on your stomach.
But that's not the case when talking about acidity in coffee, because here, acidity is a desirable quality. In fact, when coffee professionals talk about "acidity," they are talking about the presence of certain acids that influence the taste of coffee. Acidity doesn't refer to the actual acid content — it refers to a flavor note.
Because "acidity" is used to talk about how coffee tastes, you may have already heard this flavor note being referred to in other ways; words that are a bit more indicative of the flavor itself. "Bright" is a common word used to referred to coffees with good acidity.
What Acids Are in Coffee?
What acids are we talking about? In its pure state, green coffee contains a lot of different acids — good ones and bad ones. Some go away in the roasting process and others don't, so roasting is all about finding the right balance in terms of acidity, aroma, and body.
One of the main group of acids in question is chlorogenic acids, which happen to be antioxidants. These acids break down during the roasting process, which is why, as coffee expert James Hoffman writes, "the longer and darker that a coffee is roasted, the lower the perceived acidity tends to be when that coffee is brewed and tasted."
If you look at a graph of different coffee roasting levels, you will see that the darker the roast, the lower the levels of chlorogenic acid. This is why a lot of the lighter roasted coffees that are popular these days have a more pronounced acidity in their flavor profile.
In its green state, coffee has a very large concentration of chlorogenic acid compared to other plants, which is why some people get so excited talking about the antioxidant levels of coffee (even though the overall antioxidant effect of coffee is still being researched), and arabica has a lower concentration than robusta.
But there's another group of acids that plays an important role in coffee: quinic acids. As the coffee is roasted, the chlorogenic acids degrade and form quinic acids. These acids are the ones that affect the astringency of a drink, causing people to feel that sour sensation in their stomach when they drink coffee. Dark roasted coffees are high in quinic acid, but low in some of the other acids responsible for flavor.
Fresh Coffee Is the Best Coffee
It's not only roasting that has an affect on these acids: As coffee sits, certain chemical reactions with these acids occur and change the level of acidity that we taste when we drink our cup. This is why drinking a coffee that has been left for a few hours on the hot plate can literally be a gut-wrenching experience.
So want to avoid coffee that has that astringent taste? Make a fresh batch.