Coffee and Acids from our Head Roaster’s Perspective

by Erik Evenson – Zoka’s Head Roaster
I’ve been roasting coffee for almost three years now, and the most surprising thing I’ve learned about roasting coffee, is how simple the process itself is. The act of roasting consists of putting dried and processed seeds from a coffee cherry into what is essentially an oven and heating them up until the desired affect is reached.

Simple, right?


Where it gets slightly more complicated is when we delve into what is actually going on in the roaster. What complicates everything is flavor. Flavor is what we are striving to achieve when we roast our coffees. Everything is already there, present in the bean. What roasters are trying to do is coax every type of positive flavor we can from the product we are roasting.

It would be impossible to talk about every flavor compound present in coffee in this blog post. But I do want to introduce to you one of the most pronounced and important building blocks of flavor in coffee: acids.

Many people get many ideas when they hear acid associated with coffee, but basically acid is present in some shape or form in every cup that you and I drink. In fact, there are a whole bunch of acids present. I want to introduce five acids in this blog entry and, as briefly as I can, try to describe the taste sensation associated with each respective acid.

Citric acid is probably the most familiar acid. This is the same acid found in lemons, oranges and other citrus fruits.
Coffee with high amounts of citric acid will taste what we call bright. It is considered a positive flavor attribute. It doesn’t affect the aroma nor the body of the coffee.

Malic acid is an acid found in apples. Flavorwise, it is responsible for tartness. Malic acid will improve the aroma of coffee as well as the overall acidity. The presence of Malic acid is also considered a positive attribute.

Acetic acid is acid most commonly associated with vinegar. Acetic acids can be both positive and negative. It is a much more mellow acid than citric. Acetic acids can tend to upset the balance of flavor as well.

Phosphoric acid tends to taste chemically, like multi-vitamins if they sit on your tongue. They have an overall negative effect on the coffee in most cases.

Lactic acid is what is found in milk. It doesn’t change the overall flavor of the coffee, per se. Instead, the body of the coffee increases when Lactic acid is present. It is often described as giving coffee a “creamy mouth-feel.”

What does this mean for us roasting the coffee? We try to maximize the development of positive acids in the bean. We are roasting to optimize flavor, the assumption being that we have a found a quality coffee to work with and all we have to do is showcase it. As roasters, we don’t create the flavor, we try to get out of its way. We don’t add or subtract anything, rather, we coax and manipulate what is already present in the coffee bean before it ever drops in a roaster. Acids are just one of the many compounds responsible for flavor in coffee (sugars, aldehydes, etc.). The challenge for those of us roasting is to discover the full flavor potential with every batch we roast.