Acidity

Upon first take, “acidity” is a scary word. Why would we want a coffee that tastes like acid? The simple answer is that we don’t. We want a coffee that tastes balanced. What do we mean by balanced? A harmonious blend of sweetness, acidity, and bitterness - coffee is of course inherently bitter; even at the lightest roast levels, non-coffee drinkers would say that the coffee tastes bitter. In general, for us, we tend to try to minimize bitterness, and maximize acidity and sweetness. For more on our roasting philosophy, take a look at our recent blog post on roast profiles.

So what is it about acidity that makes it desirable? One way to think about it is to compare coffee to lemonade. If you make “lemonade” with just water and sugar, of course it isn’t actually lemonade at all, but the sugar-water is just sweet but bland and not enjoyable. If you make “lemonade” with just water and lemon juice, it is just sour. Of course, the obvious next step is to make actual lemonade, with water, sugar, and lemon juice. Most people would agree that this combination tastes best. The sourness or acidity (these are actually not quite exactly the same thing as there are some sour tastes that are not generated exclusively by acids, but we aren’t going to worry about that here. Generally in specialty coffee “sourness” has a negative connotation to it, whereas “acidity” has a positive connotation to it) of the lemon juice actually complements and enhances the sweetness that the sugar provides. This combination of sweetness and acidity is what we mean when we say a coffee is “juicy.” Without any acidity, a coffee would taste bland and flat.

What is highly debatable is how much acidity (and, if we’re talking lemonade, sweetness too) is enough to make a coffee taste balanced and juicy. Some people simply prefer a brighter (“bright” is yet another word that means more or less exactly the same thing as sour and acidic, generally with a positive connotation) brew than others.

One really important thing to point out when talking about acidity in coffee is that roughly 1/3 of the population has sour-bitter confusion. This means that when they taste something sour, they describe it as bitter, and vice-versa. Things that taste overly sour or overly bitter of course both taste very unpleasant, but not being able to distinguish between the two of them makes dialing in coffee very challenging as a coffee that is actually too sour requires more extraction (finer grind, more water, etc) to make it taste balanced, whereas a coffee that is actually too bitter requires less extraction (coarser grind, less water, etc) to make it taste balanced. For more on dialing in, see our practical guide to dialing in coffee. In our experience, the more people taste coffee mindfully, the better they get at distinguishing between sour and bitter.

If you are having trouble deciding whether your coffee is sour or bitter, we have a few recommendations. Vinegar and sourdough bread are foods/beverages that are very obviously sour without having much bitterness (unless the bread is burned). Dandelion greens, raw cabbage, and heavily over-steeped tea are foods/beverages that are very obviously bitter without having much acidity. Trying those can help calibrate your sour-bitter detection.

You can also brew some very dark roast coffee with a pretty fine grind in a French Press and let it steep 15 minutes with a relatively weak brew ratio (like 1:18 - 1 part coffee to 18 parts water, by mass. For example, 20 grams of coffee and 360 grams of water) to get some coffee that tastes bitter without much acidity. To get coffee that tastes very sour, use some light roast coffee with a very coarse grind in a French Press and let it steep for just one minute with a relatively strong brew ratio (like 1:14 - 1 part coffee to 14 parts water, by mass. For example, 20 grams of coffee and 280 grams of water). If you don’t have a French Press, you can literally just put your water and coffee in a mug and scoop off the floating crust before you taste it - then pull out spoonfuls off the top so you don’t end up drinking all the grounds at the bottom.

Okay, so now we have a pretty good idea of what sour and bitter flavors are, and understand that some degree of acidity in coffee is desirable. But where does the acidity in coffee come from? Remember, coffee is a fruit. Or, more accurately, coffee (the beverage) comes from beans, which are actually seeds, that are inside a fruit (the coffee cherry). One of the defining features of fruits are the acids within them, which contribute strongly to how the fruit itself tastes. Citrus fruits like lemons, limes, and grapefruits have, you guessed it, a lot of citric acid in their fruit flesh. Apples and pears have an abundance of malic acid. Grapes and berries contain tartaric acid. As the coffee cherry ripens, these acids develop in the cherry and in the bean in the exact same way that they do in other fruits. When roasting coffee, at a very simple level, the idea is to transform the raw, green, grassy flavors that are also present in the bean into sweeter flavors via the Maillard reaction, without destroying these beautiful acids.

Each individual coffee has a different acid profile, which depends on the variety of coffee bean (when browsing through our coffees, you’ll see the variety or varieties listed, like “Caturra” or “SL28” or “Gesha.” Note that these are all varieties of arabica coffee - we currently do not offer any robusta coffee), the elevation at which the coffee was grown, the soil composition, how much sunlight the trees received, the difference in the daytime and nighttime temperatures, how much rainfall there was while the cherries were maturing, how ripe the cherries were when they were picked, and more - the list goes on and on. All of these factors combined are referred to as “terroir.” The distinct acid profile of a coffee plays a large role in the subtle flavor notes that you might taste when you drink your coffee. For more on tasting notes, see this blog post.

Please note that the above discussion about acidity complementing and enhancing a coffee’s flavor profile and helping it taste balanced is really only relevant for coffees that are being drunk black. Adding milk/creamer to a coffee is actually adding acidity to the coffee (in addition to fat & sugar), so if a coffee has the right amount of acidity such that it already tastes balanced on its own, adding milk/creamer will actually typically result in making the entire beverage taste more sour than the coffee on its own would have tasted. For this reason, we do not recommend adding milk/creamer to our light roasts. Darker roasts have less apparent acidity (the pH is actually pretty much the same as it is for lighter roasts, interestingly) than lighter roasts, so adding milk/creamer can help bring the overall flavor profile into balance. Milk/creamer can “fix” darker roasts, but it generally makes lighter roasts taste worse.