Let’s continue following the flavour map by analyzing the acidity of coffee from the roasting process onwards.
Well yes, it is during the roasting process that the coffee beans acquire their final character, flavors and aromas. But before going into the details, I want to tell you the story of the first "involuntary" coffee roasting.
Coffee has been part of the everyday life of many people for more than 1000 years. It originates in Ethiopia, with the famous shepherd who noticed that his goats became overactive after eating the coffee fruits. He then decided to burn them all, because they were considered a work of the devil. When he threw the fruits into the fire, however, they took on such a curious and pleasant smell that he decided to put out the bonfire. This is how the first involuntary roasting of what would become one of the most consumed drinks in the world took place.
On average, the roasting of coffee beans lasts from 8 to 25 minutes and during this process the organoleptic profile is structured and aromas, flavors and acids are enhanced or obscured. What affects the exaltation or not is the temperature and duration and what determines the final flavour is the color of the roasted bean.
The concentration of citric acid, for example, is 1.3% in green coffee and reaches 0.6 - 0.8% in roasted coffee. Chlorogenic acids drop from 8% to 3% in an Arabica coffee. On the other hand, however, there are some acids that are produced during roasting: these are acetic, formic, glycolic and lactic acid (Godina A. & Polojac A. (2018). Caffè verde in un libro. Edizioni Medicea Firenze).
For this reason it is of utmost importance to find a balance between timing and temperature, always taking into consideration the type of bean we are handling. A more delicate one, for example, will need to be roasted at lower temperatures. However, to be sure you have found the right formula to balance the formation of the different acids, it is always recommended to do cupping after each roasting.
You heard right: even the fineness of the grind influences the level of acidity that we will then find in the cup of coffee. In fact, if we grind our beans too coarsely, it can result in acidic, watery and under-extracted coffee. That’s because, since the surface has a larger mesh, the water stays in contact with the powder less time and the first thing that is dissolved are the acids.
On the other hand, if the coffee is ground too finely, the surface of the powder is very compact and the water will remain in contact with it for too long. This can result in over-extraction, in which the coffee will be particularly bitter.
The size of the grind obviously varies depending on the extraction method you choose. Basically, however, it can be said that if we want a more acidic coffee, we should grind it more coarsely and if we want it more bitter, then we should prefer a finer grind. There's no accounting for taste!
After accompanying you through all the steps that brought the drupe to the grinding moment and after undersnding that all of them can affect the acidity of the coffee, we can talk about the extraction: the moment when the water comes into contact with the coffee powder. Also for this last fundamental step, we must follow some rules to avoid highlighting the acidity in our coffee. The first thing to know is that, as previously mentioned, acids are the first elements to be extracted, after which we will find fruity notes, then sweetness and finally bitterness and astringency.
So let's start from this last process to draw our conclusions: with a sub-extraction we will have organic acids with few sugary elements, necessary for a correct balance. An over-extracted coffee, on the other hand, will be extremely bitter and astringent because these elements will dominate over the sweetness and acidity. Finally, let's not forget our main element: water. If it is too cold, or below 90 °, there is a risk that only the acid parts will be extracted. The ideal temperature is in fact, according to the SCA parameters, between 90 ° and 96 °.