For all the Coffee addicts here, let me ask you, Is coffee an acid or a base? Anything with a pH of less than 7 on a scale from 0-14 falls in the Acidic category. With this definition holding, coffee with a pH of 4.85-5.1, would be an acid. Acidity is a prominent flavor, perceived as sweet, crisp, tart, or lively. But, well if that were the end of this story, the article would be ending here. Let’s dwell a bit more into the chemistry of it.
As stated by its pH, coffee does fall into the acidic category. Compounds that make it acidic include various acids such as chlorogenic acid, polyphenols, tannins, and so on. To add some context, orange juice has a pH of 3.3-4.2, sodas have a pH of close to 2-2.5, so coffee still is closer to the basic scale, than most of the daily beverages that we consume. (Normally, pH indicator papers, that read the pH of substances, cannot read for coffee, as the brown color makes it difficult to see the reading)
Breaking down the acidic compounds into mainly Organic acids and Chlorogenic acids, the former not only add acidity to the brew but also majorly contribute to the flavor and taste of it. Some of them are citric, quinic, tartaric, malic acids, and so on. Citric acid brings that orange-like sensation to our palate, Malic acid is responsible for that ‘lively’ taste like biting into a juicy apple. Tartaric acid can be relatable to the red wine-like flavor of coffee. Acetic acid brings out the vinegarish flavor (best to keep this one to a minimum). Quinic acid, the most interesting one in the bunch is formed from Chlorogenic acid naturally present in coffee when roasted. It’s the one that adds the astringent flavor to the coffee and maybe also a bit of ‘sour’ sensation in our stomachs, the one that’s abundantly found in dark-roasted coffees.
Chlorogenic acid which is an antioxidant in coffee, mainly breaks down into quinic and caffeic acids during coffee processing. This degradation is what majorly impacts the acidity of processed coffee from raw coffee. Lighter roasted coffees are synonymous with more chlorogenic acid, and thus a more enhanced acidic flavour profile. This acid also differs amongst different varieties.
Wandering more in time to when the beans are still in a growth phase in the cherries, citric acid, and malic acid is in production, which would give rise to a tart flavor. Another interesting fact here is that plants grown in shade at high altitudes have characteristically more acidic profiles, as the minimal stress growing conditions help them to gather higher levels of acids. Some varieties of such high-altitude coffees include Kenyan coffee, Costa Rican Coffee, and Guatemalan Coffees. Each step of processing also minutely affects the acidity in coffee. Washed beans for instance have a more acidic profile because the sucrose and fructose would get washed off, and the sugars which normally mask the acidic profile. Brewing, the most critical step in coffee making, will also impact the acidity. Higher-temperature brewing is believed to make a cup with higher acid concentrations. The more a cup of coffee sits, the more it would taste acidic, as more compounds dissolve in water. Ground size also would determine the perceived acidity in the coffee. The smaller the size, the more the surface area exposed, and the more the acid extracted in the brewing process.
Now that it is well-established how and why coffee is acidic, we can move on from this topic. But how can we discuss coffee and not talk about caffeine in the article? Well, adding a twist to this story, Caffeine is ‘Alkaloid’ in nature. Alkaloids are a class of basic substances found in plants. So, Coffee is acidic, but caffeine is basic, doesn’t add up, right? Well, let's find out why. One, Caffeine is a very weak basic. Two, it accounts for less than 1% of the dry coffee mass.
Coffee’s flavor discussion is a never-ending subject for debate. A complex ‘Acidic’ beverage, loved by all. A flavor profile studied by brewers across the world. This acidity if lacking, would make the coffee taste flat. The resultant acidity arises through a step of processes, through natural variables, through human-controlled ones, and through the ones still unknown. Enjoy your steaming cup of coffee!
References :
https://foodcrumbles.com/introduction-to-the-ph-of-coffee-is-coffee-an-acid-or-a-base/
Book: Sensory Evaluation of Coffee: Technical Unit Quality Series. No 9. International Coffee Organization. 1991. 209-243.
The Chemistry of Organic Acids in Coffee
https://www.healthline.com/nutrition/is-coffee-acidic#bottom-line
https://www.verenastreet.com/blogs/all-about-coffee/what-is-coffee-acidity
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