Coffee has already taken its place in the story of our lives. We drink it with a meal and drink it as a dessert, we drink it when hiding from the mess around or with a company of friends. Coffee is something that we regularly buy for your homes but always ready to try a new one. That is why every time we try something exceptionally tasty we want to share it with everyone. But how do we describe our coffee? We know about roast levels and won’t forget to mention its taste, but what about the acidity, a term we usually see in coffee descriptions?
In terms of acidity the first one that may come to our mind is a scientific definition. On the scientific side acidity is measured on pH scale (i.e. relative prevalence of positive hydrogen ions), where 7 is neutral and everything below is acidic. Coffee generally has an acidity of around 5 and less. So, in a scientific way of view coffee is acidic anyway, because it’s its nature. After all, coffee is a fruit.
As for coffee enthusiasts, they refer to coffee acidity as a feeling the coffee leaves in your mouth: sharp, bright, tangy or sparkling. The one thing we should catch there is that there is no ‘good’ or ‘bad’ level of acidity. Acidity is a part of coffee’s flavor, it reflects its origin and is responsible for coffee's unique characteristics.
There are different acids that can be found in coffee, but not all of them are still there after roasting. Only those that survive the roasting form the final flavor of coffee.
In arabica coffee grown at high elevations we can find citric acid. After a sip of coffee it leaves you the feeling of lemon, orange or grapefruit (if phosphoric acid is also present). Citric acid is destroyed in darker roasts. As for phosphoric acid itself, it is sweeter than most other acids and makes everything else taste sweeter as well, like making a grapefruit out of lemon or adding mango-like notes.
Malic acid is responsible for an apple or pear taste and a feel of tanginess. Chlorogenic acids are responsible for perceived acidity and a bitter taste if coffee is over-extracted. Acetic acid is also found in vinegar. At lower concentrations it can produce a pleasant sharpness, higher concentrations, though, are unpleasant and mean the coffee wasn’t processed properly. Tartaric acid makes coffee sour in higher concentrations, but produce a grape-like or winey taste at lower concentrations. Quinic acid is produced while others degrade. Its high concentration is common for dark roasted stale coffee. It gives a clean finish but is also responsible for sour stomach.
But why aren’t all the coffees the same? Why do they differ in taste even if they have the same roast level? As you’ve already guessed, they have different acidity and it depends not only on the roast level.
Coffee origin is the first step to take when in search for your ideal taste. Soil, climate pattern, humidity, it all matters and determines the specific characteristics of your favorite coffee. For example, it’s due to the prevalent citric acid Colombian coffees have notes of citrus fruits while malic acid is more common for Kenyan coffees giving them apple-like notes. The same goes for an elevation. Coffee grown at high altitudes is grown in lower temperatures with a more distinctive difference in day/night temperatures. In these conditions coffee ripens slower allowing more acids to be saved inside.
Acids are also saved better in a washed (wet) processing method because coffee beans are pulped and rinsed in water, thus removing layers of sugars. A well-known fact that is still worth mentioning is roast level. Roasting at high temperatures destroys acids. As a rule of thumb, the darker the roast, the less acids are left. But always remember that there are acids that are created by the degradation of its compounds. For example, chlorogenic acids can be broken down into the bitter quinic acid and caffeic acid.
The last and only step where you can control the level of acidity is brewing. And it has all to do with an extraction – a process of flavor and aroma compounds diffusing into the water. It starts the moment your coffee makes contact with water. Not all compounds are extracted at the same time. Fruity and acidic notes are extracted first, then follows the sweetness and then bitterness. It means that under-extracted coffee will taste sour and over-extracted – bitter.
Control extraction by:
- grind size: the finer the grind, the more quickly extraction happens;
- brew time: the longer the brew time, the more time for extraction;
- water temperature: the hotter the water, the more quickly the extraction happens.
By the way, that is why cold brew is low acid: at low temperatures extraction acids don’t extract.