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acidity in coffee

In the sensory analysis of coffee, taste is one of the main judgment factors and, together with sight and smell, guides us in the qualitative evaluation of the cup.

The fundamental taste sensations – those that we can perceive when drinking an espresso – are bitter, sweet and acidic.

If bitterness is the predominant taste in roasted coffee beans, its peculiar sensorial characteristic, its typical taste and its signature, sweetness, on the other hand, is rare to recognize but it is an indication of high quality and often associated with the perception of a fruity taste on the palate.

However, in regards to acidity, we are faced with a misunderstood and often confused taste, subject to individual, territorial and cultural tastes and preferences.

To understand and appreciate it, it is necessary to take a step back and know its origin and the factors that determine it.

What is acidity?

Acidity is a natural characteristic of many foods and drinks. It is a fundamental component of taste that produces a refreshing and spicy sensation.

Acidity is determined by the pH which varies from 0 to 14. 0 is the most acidic value, 14 is the most alkaline and 7 is neutral.

Among the flavors that we are able to perceive, acidity is the most complex. In fact, not everyone knows how to appreciate it and many tend to sweeten it to soften its intensity.

Why is coffee acidic?

Coffee has a pH that usually varies between 4 and 5 meaning it can be defined as slightly acidic.

Acidity in coffee is therefore a fundamental attribute and a key component of the general taste profile.

On the long journey from farm to cup, many factors contribute to the presence of acids in coffee.

First, acidity is a substance naturally contained in green coffee (as in many other foods) and its presence can vary based on the botanical variety or the country of cultivation/origin.
The intensity is determined by the harvesting and processing method, the roasting and finally, last in sequence but not least, the brewing.

1. Botanical variety and cultivation

There is no such thing as non-acidic coffee.

Green coffee naturally contains a certain number of acids (chlorogenic, citric, and malic) some of which are produced by the plant (organic) and others which are absorbed from the soil through the roots (inorganic).

Depending on the botanical species and the variety of coffee, but also on the environment and soil in which it is grown, different families of acids with different intensities can be found in the plant, in the fruit and consequently in the coffee bean.

In general, Arabica coffees tend by nature to have a higher level of acidity than Robusta. However, this also depends on the environment, climate and terroir in which the plant grows, as happens with grapes for wine.

Coffees grown at altitude are more acidic than those grown at low altitudes, since growth is slower and the plant is able to introduce more nutrients (including organic acids) into the fruit. Furthermore, the higher you go, the more rocky the soil becomes and richer in mineral salts which in turn tends to increase acidity (inorganic acids).

To confirm that Arabica coffees are generally more acidic than Robusta, we also have the fact that the former are grown from 900 to 2000-2200m above sea level, while the latter are found in the plains.

2. Harvest and processing

A good harvest produces a better product.

We have all tasted an unripe fruit at least once in our lives and are well aware of the harshness and roughness it leaves in our mouths.

A carefully selected harvest will produce a raw material free from defects, with a higher percentage of ripe drupes and therefore a higher concentration of sugars.

The acidity in coffee also depends on the type of processing used on the plantation to separate the beans from the drupes.

In the beginning, coffee processing had purely practical purposes, then it was discovered that, on an organoleptic level, different results could be obtained depending on the method used: washed or dry (natural).

In general, natural coffees are more balanced overall, while washed ones tend to be more acidic.

Washed coffees are affected by fermentation in water which leads to the production of acids. Furthermore, when the seed is separated from the pulp (which however contains sweetness) a series of enzymatic reactions are triggered which push the seed to develop, consuming sugars in favor of acids.

With natural processing, however, the drupes are left to rest and dry in the sun. In this way, they are not subject to any particular reaction and retain all their organoleptic properties without developing further acidity.

Another aspect to consider is the fact that the acidity in coffee does not depend only on the acids, but also on the presence of other compounds (such as sugars) which tend to attenuate it. This is the reason why natural coffees are more balanced than washed coffees, not due to the lower concentration of acids, but rather due to the greater presence of sugars due precisely to the processing method.

3. Roasting

Roasting is one of the fundamental stages in processing coffee beans. It not only makes green coffee suitable for consumption but it also confers each coffee blend its own aromatic profile and organoleptic characteristics.

Through the administration of heat, the acids present in the beans undergo a series of chemical reactions that can increase or decrease the acidity in the coffee: the chlorogenic acids (which give the coffee that unpleasant sensation of typically vegetal astringency) are significantly reduced, as well as the fresh and fruity notes of malic acid and citric acid; with the caramelization of sugars, new acids are formed, such as lactic acid and acetic acid.

As a general rule of the bean cooking process, increasing the degree of roasting leads to a decrease in acidity and an increase in bitterness.

The lighter the coffee is roasted, the more acidic it will be in the cup. On the contrary, the more it is roasted, the more the acidity will tend to attenuate in favor of bitter and burnt hints if the roasting is too strong.
In other words, the darker the color of the coffee becomes, the more the acidic sensations in the coffee decrease and the bitter ones increase.

You need to find the right balance.

Only the experience of the roaster can develop roasting profiles that enhance the complexity and balance of the aromas, highlighting the natural acidity of the coffee, without increasing the concentration of unpleasant acids and bitter compounds. With the declared aim of obtaining the perfect cup.

At SpecialCoffee we have developed the ability to refine the roasting process according to the blend of coffee to be roasted as well as the specific use of the product, the market, and the reference country where the coffee will be used.

4. Brewing

Brewing also represents a key element in determining the acidity in coffee.

To understand the influence of this phase it is necessary to better understand how it happens. Brewing is the moment in which the water (liquid) comes into contact with the coffee (solid) and dissolves all its components, giving rise to our drink.

However, not all the substances contained in coffee dissolve at the same time: acids specifically are very soluble and are the first to fall into our cup. So if a coffee is extracted in a short time, the perception of acidity will be greater.

So how can we obtain perfect brewing? Knowing and controlling the parameters that influence brewing methods and times.

The first element to consider is the grind.
In general, the finer the coffee is ground, the more the contact surface with the water increases, prolonging the brewing time and, therefore, the presence of bitter compounds.
On the contrary, with a coarser grind, the contact between the two elements, and the brewing capacity, will be lower. In this case the perception of acidity in the coffee will be greater.

Another element to consider is the dose.
An insufficient dose of coffee can lead to too rapid extraction, and therefore to excessive acidity.
On the contrary, an excessive dose can cause too slow extraction, and therefore a coffee with a perception of insufficient acidity.

The brewing capacity is ultimately influenced by the water temperature.
Normally, hot water between 90° and 95°C is used to extract coffee. A higher temperature can lead to too rapid extraction and a perception of excessive acidity in the coffee.
On the contrary, a lower water temperature can lead to too slow extraction and an almost imperceptible perception of acidity, resulting in a cup that is too flat.

To demonstrate what has been said we have the practical example of under-extracted or over-extracted espresso.

Normally, it takes around 25 seconds to brew an espresso. Therefore grinding, dose and temperature must be adjusted so that brewing takes place in this time.

If the grind is too coarse, or the dose is insufficient, or the water is too hot, the brewing time will be shorter, the espresso will drop quickly and be under-extracted, resulting empty and acidic, with insufficient crema and a light colour.
On the contrary, if the grind is too fine, or the dose is excessive, or the water is too cold, the brewing time will be longer and the espresso will be over-extracted, i.e. with a marked and unpleasant bitterness, a dark colored cream and presence of whitish bubbles.

Acidity in coffee: yes or no?

In conclusion, should the acidity in coffee be considered an advantage or a flaw?
It’s all about balance!

If well balanced, the acidity in coffee is to be considered an asset. It is indeed an indicator of quality as it adds depth and complexity to the other flavours.

For an excellent coffee, however, it must not be too intense or absent. Otherwise, the cup would be unpleasant in the first case or flat and “toneless” in the second.

The key word is therefore always balance: to be best appreciated it must be in balance with all the other taste sensations, without overriding them, so as not to be recognized as a defect.

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