Let’s talk about acidity

In the lab

Let’s talk about acidity

angel barrera | 2019-04-09

We heard talk about acidity in coffee quite often , with discretion from the roasters, trying not to frighten consumers… words as brightness, citric notes and others are used for consumers not to be afraid of acidity and what it represents for coffee. Why? Because people normally relates acidity with those drops of lemon that we saw go directly into our stomach, this stab we get every time we go to a bistrot and have a coffee… But acidity in coffee is absolutely not that, it is one of the most important tastes needed in every little cup of the black beverage. It is perhaps the most important and representative parameters when we differentiate a complex coffee from a flat one.

 

But what is exactly the acidity in coffee?

For being graphics in our explanation, a bright coffee is like a soda which has just been opened (sorry for the heresy), with all of its bubbles that climb into your mouth… if you leave this soda opened for a while, and take it back a couple of hours later, you’re going to feel a drink with no more bubbles and flat. This is what looks like a coffee without acidity: neither bright, nor complex! It is for this reason that acidity is extremely valued in coffee!

The acidity is mainly related to terroirs where coffee is cultivated (coffees in Central America, for example, are very appreciated for their acidity). Then, some others parameters influence the acidity as when and where the coffee is produced (such as volcanic soils or the under shade culture) or its transformation process (like how it is processed, washed or natural, with or without fermentation, etc…). Once that coffee is green, some other factors are still going to influence its acidity: roasting color & profile, and of course, how it is going to be brewed.

It’s already quite complicated, isn’t’ it?... well, some roasters kind of made a weird face when, in Colmar’s coffee show, we started talking about a coffee having an acidity said “malic”.

 

Are there different acidities in coffee?  

Oh yes… The coffee, which knows no limits when talking about aromatic complexity, couldn’t be happy by having only one acidity!

There are different types of acidities. Chemically, we found principally 3 kinds of families of acids, which names that we will avoid to mention this time not to make you afraid of keep reading. These groups of acids are then decomposed into different acids which we found into coffee. There are four of them that we found the most and in more important proportions in coffee: citric, malic, acetic and quinic (for this time, we will leave palmitic for coconuts!).

The 3 first ones are desirables, and the last one is the undesirable.

  

How can we recognize them?

The citric acid is the most common, you can found it in maximum proportions as the harvest is fresher. In mouth, this is the acid, as its name says, that makes us remember a green lemon and any kind of citric in general.

The malic acid is a bit weirder, but not unknown to us, it is the acidy that, in mouth, feels like a green apple. Different from the citric acid, the malic acid is not as explosive and is rounder in mouth. A coffee, of which we recently talked about, has become certainly the ambassador of this acid!

The acetic acid, which starts being a bit dangerous, being sometimes related to vinegar… It is an acid that, in mouth, makes us think on wine, and sometimes, has this winy mouth feel sensation which make us related it directly to the body of the drink. The acid, by nature, of natural coffees…

Finally, the quinic acid is the bad brother of the four. The fourth Karamazov. It comes directly by degradation of the chlorogenic acid (and acid, which as well, is largely founded on robustas) during the roast. This is the reason why, different from the others, it increases as the coffee gets darker. And old roast plus a cup getting colder would make it easily come out. In mouth as in the stomach, it is the acid (barely bright) which would be like a fine stab.

So our question was: are we capable of identifying them?

Leaving aside professor boring, we will explain you what we did on our lab to be able to find them!

The experience

To start, we identified four coffees that we thought we could find the different acids (one per coffee).

For the citric acid, we choose our FW coffee from El Manzano farm of El Salvador.

For the malic acid, we choose our coffee from the Mpanga Station in Kayanza, Burundi.

And for the acetic acid, we choose our coffee from Mesela, Harrar.

We roasted these 3 coffees in 3 different roasting colors (light, medium and dark). Play with 3 different colors allowed us to have larger amplitude where different acidities could be present. We did a regular Brazilian cupping for this test.

For the quinic acid, we used a 50% combining a third of each of the 3 coffees roasted dark and a 50% of a coffee roasted 3 weeks ago and clearly darker.

With four coffees so different from each other, and having on mind very precise terms such as lemon, green apple, wine and puaj, we were able to differentiate, in blind, each of the different acidities.

This first exercise was only to being able to identify the four different acidities.

We tried later, to force some parameters (theoric ones) which allowed different acidities to expressed better on coffee. We tried mainly to play with 3: grinding, infusion time and water temperature. Being the optimal temperature (yet, theorical), to get all the different acidities the same (94°C), we erased it as an isolated parameter, we used this temperature however, for the other 2 parameters. We did these tests using a French press, for how easy it would be to measure both of these parameters with this coffeemaker.

We used still the same four coffees, with a roasting color known as medium roast.

With the grind test, we used a very fine grinding for all the coffees, using only a very coarse grind for the Harrar. The results were clear; we could easily identify all the acidities. But above all, what amazed all the team was that by playing with the grind we were able to obtain acidity as if the coffees were roasted extremely light!

For the infusion time, we infused the blend dark & old (for the quinic acid) in 20 minutes (please bar owners, do not leave your coffees over a plate for hours!), l’Harrar during 15 minutes and the Burundi & El Salvador only during 5 minutes. With these parameters, we could identify the acidities, being the hardest the one of the quinic against the acetic one, since the coffee gets colder.

 

Just to end

But, why is it important to be able to identify the different acidities of a coffee?

Just to start, to understand the coffees you workwith … This will allow you to know how you’re going to:

Roast it, an acidity too high would be decreased by doing a slow roast… as well, the color of the roast will have an incidence in a coffee made for espresso!;

Blend it; by playing with different acidities and how you treat them, you could be able to get an interesting and original complexity in a cup… it is up to you to surprise your costumers! And finally;

Brew it, who would tell you that coffee with high acidity won’t be suitable for an espresso as pure origins? A malic acidity, like the one perceived in the Burundi coffee, would be a pure tangerine, and round, in a small ristretto!

The coffee is but a brut metal… it is up to you to become its alchemist!

Until the next one,

The Belco team

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