The Science Behind Coffee Acidity
Evaluating coffee acidity can be tricky. I experienced this firsthand during my first cupping session, 7 years ago.
“Mm, cranberries, with a distinctly orangey acidity… mm… and red wine,” said the barista to my right, furiously jotting this down on his little notebook.
“Oh yeah, definitely a bright orange, but maybe more like tangerine?” the other barista to my left chimed in.
“Oh yeah, tangerine, definitely orangey,” I nervously added, desperate to seem as avid a coffee geek as everyone else at the table.
But really, all I was thinking was: “What the hell are these people on?! This just tastes like slightly sour coffee! What am I missing here?”
Spanish Version: Ciencia del Café: ¿Qué es la acidez?
Coffee cupping. Credit: Vertical Coffee
I used to have the hardest time deciphering “flavour profiles” and “flavour wheels”. It all tasted like, well, coffee to me. Sure, some were more sour than others and some more bitter than others, but they were still coffee.
Eventually, I figured it would be easier to just remember the names of the different varieties of coffees, and then memorise the associating flavour profiles or coffee acidity. And that is how I managed to scrape by as a mediocre barista for the next couple of years, bluffing my way through cupping session after cupping session, “really knowing what I was talking about” – even though I literally had no idea what I was slurping from my spoon.
I eventually grew frustrated by this façade and decided that I wanted to actually learn something at a cupping session. (Hello, that’s why I was going, wasn’t it?) I wanted to be able to get as genuinely excited about tastes as everyone else around me. I wanted to have my own opinions, instead of parroting everyone else’s.
That’s when I decided to study up on food science and figure out what actually went into coffee, chemically speaking. I was specifically interested in this magical coffee acidity that everyone else seemed to be getting so hyped up about.
Here’s what I’ve managed to learn, in a way that made the most sense to me – and hopefully will for you, too.
Coffee Acidity for Dummies
Acid is a chemical substance that is characterised by a sour taste. In fact, the word “acid” in Latin literally means “sour”. Aqueous solutions of acids have a pH of less than 7 and the lower the pH, the higher the acidity.
Coffee and flavor wheel. Credit: Commonwealth Joe Coffee via Long and Short Coffee
Acid is a naturally occurring product in tonnes of foods, like lemons, vinegar, yoghurt, and even coffee. There are literally hundreds of different acidic compounds in coffee alone, ranging from the familiar (like citric acid) to the huh-wha-what?? (like 4-monocaffeoylquinic acid). But for the purpose of this article, I’m going to only talk about the primary acids that affect taste.
- Citric Acid
Citric acid, like its name suggests, exists in high concentrations in citrus fruits. In fact, it can make up almost as much as 8% of the dry weight of these foods. It’s undoubtedly the most commonly occurring acid in all fruits and vegetables, as well as the easiest to identify.
Coffee brewed on a Chemex with orange slices. Credit: Jay La Mode
- Malic Acid
Malic acid has a flavour that is most often associated with green apples (after all, it was derived from the Latin word “malum”, meaning “apple”). You’ll find malic acid in its purest form in rhubarb, in which it makes up the primary flavour.
In the culinary world, malic acid is commonly associated with limes, but it’s much easier to think of it as “unripe fruit flavour”. The acid generally decreases in concentration with increasing fruit ripeness, so anything green like green grapes, kiwis, or gooseberries would be on the cards.
Green apples. Credit: Holly Mindrup
SEE ALSO: Coffee Cupping: 5 Key Steps to Cupping Mastery
- Tartaric Acid
Tartaric acid is commonly associated with grapes, due to its high concentration in the fruit. That’s not the only place you’ll find it, though. Its salt, potassium bitartrate (commonly known as cream of tartar), develops naturally in the process of winemaking and is commonly used as a leavening agent in food preparation.
Grapes. Credit: Maja Petric
The most striking feature of tartaric acid, taste-wise, is its mouthfeel. It causes a craaazy amount of mouth-watering and leaves an astringent aftertaste. In fact, it’s one of the main ingredients in “super-sour” candies and gobstoppers.
Ever had these as a kid? Credit: Sylvanus Urban
- Acetic Acid (aka ethanoic acid)
Acetic acid is special. Aside from a very characteristic vinegary taste, it also has a pungent vinegary smell. At lower levels, this can give it a pleasant sharpness or lime-like flavour, but in higher concentrations it just tastes – and smells – like fermentation.
This funky taste and smell, particularly when paired with other flavours (especially sugar), can lead to a winey or champagney kind of flavour.
Acetic acid: vinegar or wine?
pH Levels and Coffee Acidity
So right now you’ve got a pretty good idea of what different acids are, and what they taste like. But what does this have to do with your coffee tasting like oranges?
The easiest way to understand coffee acidity is to think of it as an abstract concept. “Orange acidity” doesn’t mean that your coffee literally tastes like oranges. Its true meaning is something closer to “it is as sour as an orange”.
If you think about this explanation, suddenly tasting notes begin to make more sense. Since blueberries are less acidic than, say, lemons, a coffee with “blueberry acidity” would undoubtedly be less sour than one with “lemon acidity”. Makes sense, right?
To help illustrate this model, I made a rudimentary chart associating common fruits with their corresponding pH values. You can, of course, find much more detailed and extensive charts on most food science or FDA type sites (although they may not be so focussed around coffee).
How acidic is your coffee? Credit: Christine Seah
Combining Flavours and pH
You might have noticed that in the pH scale, some fruits have similar pH values even though they taste completely different. Take apples and oranges, for example. So how does this work?
In the case of apples and oranges, the predominant acid within the respective fruits is different. Green apples consist primarily of malic acid while oranges are filled with citric acid.
Imagine a lovely, bright, light roasted African coffee. When brewed, it reads at 4.6 on the pH scale, so we’re looking at grapes, peaches, plums, pineapples, and so on. Then you notice that it leaves an astringency in your mouth that’s characteristic of tartaric acid. You could probably define this as a “grape acidity” or, well, anything from the sour stone fruit family (e.g., sour cherries, plums etc). A combination of this grapey acidity and the ferment-y flavours of acetic acid could even give you a winey type of acidity.
Similarly, a citrusy flavour with a low pH could be identified as “lemon acidity”, while a higher pH could be closer to orange. More malic acid flavours with a lower pH could be lime whereas a higher pH could be categorised as rhubarb, green apples, or even grapefruit.
Once you understand all this, cupping and understanding coffee acidity becomes a lot easier. Forget faking it, you just understand it.
Refining Your Palate
It’s always good to practice your cupping skills by sampling a wide range of flavours. Nothing helps sharpen your palate for coffee acidity more than tasting various acidic things!
What I’ve done in the past was to buy these various acids in their pure form and make a 1-2% solution of each with distilled water. This is perfect for beginners. The results are truly quite distinct since you don’t have to taste through all the other flavours like sweetness or bitterness.
Acidic test. Credit: Lizzy Ferry
After getting a clear idea of what the pure acids taste like, move onto some actual food. Get a massive platter of fruits, vinegars, and even wines, and start categorising them according to what acid you taste the most in them.
Coffee tasting with different fruits. Credit: Klatch Coffee
The thing about cupping is that, once mastered, it both helps you to understand coffees and makes drinking coffees much more fun. And while acid profiles can seem intimidating, once you know what you’re looking for, they’re actually pretty easy to distinguish. Before you know it, you’ll be an acid expert.
What was your first cupping session like, and how did you feel about acidity in coffee? What are some ways you think acidity could be simplified in the tasting process? Let us know in the comments, on facebook, and on instagram – we’d love to hear your stories.
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