Let’s start with knowing what acidity is. Acidity is not that easy to define, mainly because it takes on many different forms.
A coffee that’s more acidic affects the flavor and the aroma, taking on the characteristics of stone fruits, sweet nectarines, or juicy apples. It can be understood as a mouthfeel. You can define acidity by the sharpness the coffee leaves in one’s mouth. No sharpness: no acidity or very low acidity.”
But acidity is also a chemical compound, and the exact type of compound that will affect the coffee’s taste. Understanding a little bit of coffee chemistry can help roasters (and even brewers) to get the best possible flavors in the cup. Too much acidity can make a coffee taste sour, but not enough acidity will make it taste flat.
Let’s go a little deeper. Acidity through the microscope. Organic acids include citric, malic, quinic, acetic, succinic, and tartaric acids. These are the “good,” fruity acids that you want to taste in the cup. All of these have their own additions to coffee. Malic is the same kind of acid you get in green apples. Citric, as you probably already know is citrusy. Tartaric is more grape-like, although surprisingly it does show up quite a bit in bananas, and acetic is like vinegar.
Then you have chlorogenic acids, which get broken down during the roasting process into quinic and caffeic acids. The thing is, quinic acids are not a good taste. These compounds are responsible for bitterness, astringency and sourness in the beverage. For this reason, often the darker the roast, the more bitter it is, while the lighter the roast, the more acidic it will be.
No matter how you brew or roast them, some coffees will always be more acidic than others. Factors such as the origin, variety, processing method, and climate have a huge influence on this.
Origin has certain type of soil characteristics and a certain amount of a certain acid. This plays an important role in the perceived acidity of your cup of coffee. Part of this is just genetics. Yet part of it is also because of the farming conditions. Certain varieties are more suited to being grown in cooler temperatures than others – and that also has an impact on the flavor.
The most coveted coffee beans are typically grown at higher elevations, although if we’re honest, this has more to do with temperature than altitude. Coffee that is grown at cooler temperatures tends to ripen slower, allowing the development of more complex flavors. When brewed, it tends to be more acidic and aromatic than those coffees grown in warmer climates.
Now, on to controlling acidity in the roasting process. You cannot create a flavor, in roasting or brewing, that a coffee doesn’t have. However, you can roast it in a way that will highlight or obscure the acidity. First, you can consider the roast level. Most acids decrease in concentration during the roasting process. But roasting isn’t just about how long you keep the beans in the roaster. It’s about how you manipulate the heat and airflow throughout to enhance the coffee’s best characteristics. High heat tends to draw out acidity. Just be careful not to go too high. Your aim should be an early first crack.
Lastly, let’s get down to brewing. Aim for a relatively high water temperature but a coarser grind size and shorter brew time for a more acidic cup. Grind finer and brew for longer if it’s coming out sour. Or, brew cool to avoid acids, but don’t forget that you’ll need to increase your brew time, since extraction takes longer at lower temperatures. Don’t forget it’s all about the balance.
Acidity is an extremely complex subject. It consists of many factors affecting the presence or absence in your coffee. One of the most wonderful things about coffee is that there are so many notes, flavors, and aromas. Certain roasts, varieties, processing methods, and origins will offer different degrees and types of acidity.
Remember acidity gives coffee it’s liveliness, and balance.