The thorny question of acidity

Although some try to avoid it, the acidity is worth so many points, when the experts assess a batch of coffeeQ Graders, as aromas, flavors and body. Indeed, without any acidity, a coffee can quickly fall flat, while too acidic, it can become unpleasant. The roasting will either serve to enhance the acidity or to attenuate it, in order to obtain a more balanced profile. After being questioned about this, the Société des Cafés team wanted to talk about this characteristic, which is not unanimous in terms of preferences.

Chemically speaking, it is fair to say that all coffee is slightly acidic, since its pH is below 7 (neutral pH). Like bananas, figs or pumpkins (foods that we don't intuitively describe as tart), the pH of coffee is around 4-5. However, when you are told that a certain washed coffee from Ethiopia has a vibrant acidity or that such a coffee from Colombia has an acidity reminiscent of lemon, it is obviously not its pH that we are referring to. Rather, it is the presence of acids in the grains and their effects on our perception of flavors (aromas and flavors).

Although coffee can contain hundreds of different acidic compounds, we limit ourselves here to two categories, organic and chlorogenic, which affect, above all, our taste experience. The former are present in both green beans and roasted beans and generally add positive aromatic qualities to coffee. Here are five of the most common types of organic acids you find in a cup:

• Malic acids give coffee a flavor that is more often than not associated with green apple. In the culinary world, the taste of malic acid is also linked to that of unripe fruit. To spot it on taste, other benchmarks might be green grapes, kiwi or pear.
• Citric acids provide citrus notes (lemon, orange, lime, etc.). A taste that is easy to identify, since it is present in a large majority of fruits and vegetables.
• Phosphoric acids are sweeter. Balanced well with citric acids, they can give coffee an aromatic profile reminiscent of red grapes, mango or blackcurrant rather than simply emphasizing citrus notes.
• Tartaric acids s are found naturally in fruits such as bananas, cherries and grapes. The most striking characteristic of tartaric acid is its mouth feel: it stimulates the production of saliva, then leaves an astringent aftertaste. In high concentrations, this acid can produce an undesirable, safe taste, while in small quantities it can add wine to coffee.
• Acetic acids can give coffee special features. Often, in high concentrations, we perceive a taste and odor of vinegar or fermentation. For some, this defect means that there were gaps in post-harvest processing. In smaller amounts, the presence of such acids brings out lime notes or a tangy sensation.te¹. Paired with other compounds (especially sugar), this taste can lead to a winey aspect, sometimes reminiscent of champagne².

The second chlorogenic acids decompose, normally during roasting, inton quinic acids and in caffeic acids . Studies show that in medium roast coffees the chlorogenic acids are broken down by around 60%, while in dark roast coffees it is up to 100%. Although some of the chlorogenic acids are known to turn into quinic and caffeic compounds, this disruption process could lead to a myriad of other reactions, which may or may not affect the taste of the coffee. Their fate is still unknown. Additionally, there is no scientific consensus on how quinic acids and caffeic acids influence the flavor profile of a coffee. One hypothesis put forward suggests that quinine compounds have an astringent, sometimes even metallic, taste. They would be responsible for the bitterness and sourness of a coffee. Thus, by further roasting, the more chlorogenic acids would break down into quinic acids, the more pronounced this taste would be. This would explain, in part, why these characteristics are predominant in dark roast coffees as well as in stale coffees.³.

So what are the factors that contribute to the perception of acidity in coffee?

The acidic profile of a coffee is formed and defined throughout the production chain: from the fruit to roasting to the way you prepare it. All of these steps have an impact on the type of acids as well as the amount of each you will end up with in the cup. Note that some coffee beans already have more organic acids than others, depending on their origin and the conditions in which the fruits developed, as well as the processing method used. To put it another way, some batches of coffee, even before being roasted, are more conducive to revealing tangy qualities.

1. Origin and climate

The country, even the region, where a coffee comes from can influence the components of the beans. Each type of soil brings its characteristics to the coffee cherries which, for their part, incorporate certain acids in varying quantities. For example, the soil of Kenya contains more malic acids which give, let us remember, an acidity closer to that of green apple, while in Colombia, citric acids are prevalent. We also note that the coffee plantations located on volcanic soils, since formed by rocks rich in silica, produce more acidic coffees.

The climate to which the coffee trees are subjected is also important. Often, the elevation of the farm is referred to as a significant variable. However, the significant variable lies rather in the climatic conditions resulting from such a height. Slow ripening of fruit under these conditions allows more nutrients to accumulate. The result: more sugars and organic acids in cherries. Slowing fruit formation is also possible when plantations are covered (Shade-grown coffee). During plant growth and fruit ripening, cellular respiration results in the formation of chlorogenic, citric, malic and phosphoric acids. Lengthened by the cool temperatures implied by the shade and the high altitude, this ripening period allows the coffees to store more acids, such as caffeine and sucrose.⁴.

2. The variety

We know that the acidity of a coffee is also influenced by the genetics of the Coffea type as well as that of its sub-varieties. Already Arabica varieties tend to have less chlorogenic acids than its counterpart, Robusta. This abundance of chlorogenic compounds is, at least in part, responsible for the organoleptic distinctions between the two species, Robusta having a more bitter and vegetal taste than Arabica when roasted. In addition, due to their genetics, some Arabica varieties such as SL-28, SL-34, Catuai or Caturra are more conducive to letting a lively acidity shine through.

Some of the acidity is therefore explained by genetics. But that's not all, as it is more than a matter of adaptation. Some types of coffee trees are more acclimatized to high altitude cultivation, involving less oxygen and cooler temperatures, while others prefer low altitudes, which will also have an impact on the acid compounds incorporated into the beans. In this, some varieties of coffee can generate more acidity if planted in the right place.⁵.

3. The treatment method used

To separate the coffee beans from the fruit,some methods have been developed, the best known of which are natural processing, washed and honey. These methods obviously have an effect on the final flavor profile of a coffee and are chosen and used for that. For example, for lovers of tangy coffee, washed coffees seem to be the perfect choice. The grain washing process (pulping, rinsing) simultaneously removes fructose and sucrose, leaving a high level of acidity. As for the natural treatment, the latter involves leaving the fruit intact before spreading them on drying beds. This process increases the sweetness in the cup and therefore lowers the perceived acidity. Honey coffees are halfway between the two. By leaving some of the mucilage on the grains during drying, we make sure to keep some of the fruit's sweetness while developing a well-defined acidity⁶. We therefore understand that we will favor washed coffees if we want brilliant acidity, honey coffees for lively acidity, then natural coffees for softer acidity.

4. Roasting

As pointed out in the introduction, roasting will serve to enhance or reduce the acidity of a coffee. This process converts and breaks down chlorogenic acids, causing the formation of quinic and caffeic acids, while altering the level of organic acids in the beans. Further roasting will tend to camouflage a coffee's natural acidity, while lighter roasting will keep it better.

While the length of time the beans are exposed to heat is important when it comes to acidity, controlling the temperature and air intake also help bring out the best characteristics of a coffee. In the article« How to Roast for Acidity», the key is said to be a high temperature to really bring out the acidity while maintaining a certain balance so it doesn't burn the coffee and hide its sweetness. The other goal is to produce a first crack in the bean that doesn't last too long and comes early in the roasting process.⁷. It will be understood: roasters must know their beans. Everything is in balance to prevent the coffee from losing its acidity or, conversely, becoming sour.

5. Preparation

When you brew coffee, you want to extract it correctly so that you can see the acidity as part of the whole. Fruity and tangy notes are extracted first, followed by sweetness and finally bitterness. This means that an under-extracted coffee will lead to a safe taste, as it doesn't have the sweetness and hint of bitterness to balance the acidity, and an over-extracted coffee is obviously going to be bitter. To achieve a balanced result, you must first think:

• At the grinding. The finer the grind, the faster the extraction will be, since the surface of the beans in contact with water is greater. A coarser grind means that the extraction will take place more slowly. Thus, for more acidity, a coarser grind is preferred. For less acidity, a finer one. In addition to this basic principle, you must also take into consideration the grains you have on hand. Darker roast coffee tends to be more soluble than light roast; its extraction will therefore be done more quickly. In this specific case, we favor a coarser grind if we want to let a touch of acidity show through.
• At preparation time. The extraction time and the preparation time are not the same. Extraction time means the time it will take for soluble elements to pass through water. Preparation time is more the contact time between water and coffee. The longer the preparation time, the more elements are extracted from the beans, always starting with acidity, sweetness and finally bitterness. Shorten the contact time for more acidity, lengthen it for less.
• At water temperature. The hotter the water used, the faster the soluble compounds from the grains are extracted. Cooler water slows extraction time. However, be aware that some compounds cannot be extracted at certain temperatures. We just have to think of the Cold Brew, which is usually not very tangy. For some, the ideal for achieving strong acidity is to keep water around 94C (202F) and modify the other two parameters so that, by lowering the temperature too much, certain desirable aromatic compounds of the coffee are not left out.té⁸.

Now you can make a difference or lessen the acidity of a coffee with full knowledge. Know that you cannot put forward traits that a coffee does not have at the base. This is why all the factors (terroir, variety, processing method and roasting) must be taken into consideration before making a choice. More simply still, for those who wish to avoid any acidity, we will target natural coffees, lower altitude and slightly more roasted. For those who want to make it shine, we prefer washed coffees, high altitude and light to medium roast.

Research and writing by Chloé Pouliot
Correction by Suzie Genest

References:

1.Acidic Coffees: A Brew & Roast Guide, Perfect Daily Grind.
2. For the whole section:The Science Behind Coffee Acidity, Perfect Daily Grind.
3.Coffee Roasting Chemisty: Chlorogenic Acids, SCA News.
4.The Academics of Acid in Coffee, Five Senses Coffee
5. Acidic Coffees: A Brew & Roast Guide, Perfect Daily Grind.
6. The Academics of Acid in Coffee, Five Senses Coffee.
7.How to Roast for Acidity, Perfect Daily Grind
8.How to Increase or Reduce Coffee Acidity During Brewing, Perfect Daily Grind.