You’ve probably heard a barista describe a coffee blend as acidic.
But what does that mean?
Sometimes they are describing flavor notes. Sometimes they’re warning someone who has heart burn that this could upset them. And sometimes they’re helping someone understand roast.
All of these are true ways to discuss coffee acidity.
We’re going to look at middle school chemistry, the roasting process, and the digestive system so that you can better understand what makes good coffee, and how it effects you.
The smallest of details.
pH stands for pondus hydrogenase or power of hydrogen scale.
It measures how much hydrogen is in a liquid. It ranges from 0-14, with 10 micro-increments between digits.
It’s important to note that the presence of hydrogen at all, is a complex thing. Hydrogen is constantly on the move, binding and breaking off from water molecules. Leaving hydrogen ions and hydoxide ions in its wake.
Two extremes
0-7 is acidic, meaning there are more hydrogen ions present. The Encyclopedia Brittanica defines a hydrogen ion as “the nucleus of a hydrogen atom separated from its accompanying electron.”
Pure water is neutral in the middle of the scale at 7.
On the opposite end of the spectrum 7-14 are alkalines or “bases.” Alkalines are marked by the presence of hydroxide ions. If a base comes into contact with a solution, it readily takes hydrogen ions. This leaves H2O lacking 1 hydrogen molecule, which yields more hydroxide ions (OH-)
A few substances you may find on the acidic side of the scale are rainwater, soda, lemon juice and battery acid. On the alkaline or base side, you’ll find sea water and cleaning solutions.
What does this have to do with coffee?
Let’s look at what happens to your body as take that very first glorious sip of your morning coffee.
Although everyone’s body chemistry is different, it is safe to say that coffee is acidic. According to Science Buddies, a standard cup of black coffee ranks in at 5 on the pH scale. The proof of it’s acidity is found on the taste receptors. Even though everyone’s taste buds respond differently to the acidity of coffee, the chemistry works the same. The hydrogen ions in our coffee activate our digestive system as soon as it touches our tongue, triggering gastric acids in the gut to get pumping. (This is why people who deal with acid reflux or heart burn should typically stay away from coffee. They already have too many enzymes lingering along the upper gastrointestinal tract to begin with.)
In most cases though, the acidity in coffee usually leads to better digestion.
You’ve probably heard the term “soluble fiber.” It’s one of the dietary fibers that you need to keep things moving and metabolizing through your system. Soluble fibers lower cholesterol levels, which protects your heart against disease. The nature of its solubility feeds gut flora which promotes general digestive health, as well as helps you maintain or lose weight by regulating bathroom trips.
If you’re looking to add coffee to your daily routine for these awesome benefits, it’s important to remember that 4 cups a day will only provide 7% of daily fiber needs according to sciencenews.org.
It’s also imperative to keep count of how much you are consuming. Too much caffeine in a day can lead to symptoms that do more harm than monitored intake can do good. To read more about suggested safety measures for your coffee routine, check out my last article here.
Although coffee is innately acidic, the level of acidity is controlled by the chemical composition of the coffea plant as a whole, the soil it grew up in, and the roasting method.
Acidity and Flavor Notes
Coffee acidity is praised among die-hard coffee lovers when it comes to South American blends. The soil there is mineral rich and the farms are at a higher altitude, which predispositions the beans to yield more of those yummy acids.
Of course the opposite is true for farms at lower altitudes, they tend to produce more neutral beans (less acidic). In fact most of our favorite low acid k-cups are grown at lower altitude and roasted darker to remove even more acid from your cup.
You may be thinking though, “how can acids taste good?”
Acid typically gets a bad rep because it brings images of destructive acid rain and corrosive battery acid to the mind’s eye.
But acids dictate a lot of the flavor and mouthfeel of a cup of coffee.
There are 5 main types of acids that are prevalent in the most common coffee blends. In descriptions, either from a barista or on the side of the packaging, you tend to see that roast masters liken acids to fruit. This is the easiest way to convey acids to people without scaring them away. The mention of fruit brings quick remembrance to peoples palates and sense of smell.
Let’s dive right in to the different types, examining why the plants need them and how to identify them in our roasts.
Citric Acid
The word, “citric” immediately reminds most people of the zest of oranges, lemons and limes. Keep that in mind.
Citric acid is formed during the growing cycle of a plant’s life. During this process, the plant takes sugars and turns them into energy. Citric acid is a direct byproduct of this chemical reaction.
Typically, the healthier the coffea plant is, the more citric acid is stored. So if you really taste that zing at the tip of your tongue at a coffee tasting of any shape or form, you’re experiencing citric acid at it’s finest.
Sourness, however, is an extreme of acidity and can be considered a coffee defect.
Don’t mistake a bad batch for a citrus forward one.
Malic Acid
If you are a wine connoisseur, as well as a coffee fanatic, you have probably heard this term from well-informed vintner at a winery.
It is often used to describe the astringency of a mouthful of wine.
It’s also what makes apples taste so juicy and fresh, and sometimes pleasantly sour.
Malic acid, or C4H6O5, is found in everything that breathes.
Think of this chemical compound as the next step of the citric cycle I mentioned before. As the citric acid is spent, it turns into malic acid as a defense mechanism for its leaves. The malic acid content gets stronger the more the plant is tended, just like citric acid. When taking this little fact into account, the way it manifests on the tongue and in the mouth makes sense. In nature, the coffea plant produces malic acid to stop critters from eating away at their fruits.
But for us, the acidity pairs and enhances the sweeter notes within the complex coffee bean.
Phosphoric Acid
Unlike the two mentioned above, phosphoric acid is not linked to the healthy growth of the plant, but one of the necessary ingredients to any growth at all. Soil!
The presence of phosphoric acid is a direct effect of the amount of phosphorus in the soil.
According to the University of Nebraska in Lincoln, “Phosphorus is a component of the complex nucleic acid structure of plants, which regulates protein synthesis. Phosphorus is, therefore, important in cell division and development of new tissue.”
The best way to figure out if your coffee is rich in phosphoric acid is to close your eyes and slurp. Phosphoric acid is responsible for the lingering feeling in the body of the coffee. It sometimes shows up on the sides of the tongue and mouth. It’s often described as chocolatey and velvety.
You usually note this experience in dark roasts, especially those of African origin.
Lactic Acid
The word “lactic” is usually affiliated with dairy products: cream, cheese, yogurt- you get the picture.
If that was your initial reaction, you’re right on target.
In milk, lactose manifests during the fermentation of milk.
Same situation here.
Lactic acid manifests during the fermentation process of a coffea fruit. You may be bewildered by the idea of fermenting and coffee even being in the same sentence. A little known fact, fermentation is the best way to do away with the fruit without damaging the seed (bean.) During that process malic acid is met by yeast and yields lactic acid.
If you ever feel a lingering fruity, yet wholesome note on the back of your tongue, you’re experiencing lactic acid.
Acetic Acid
If this term seems familiar to you, but you can’t quite place it, the word you’re looking for is… vinegar.
Before you click off the page because vinegar and coffee sounds disgusting, hear me out. This sharp taste and feeling enhances the entire experience of coffee in the right proportions.
Acetic acid is another by product of the fermentation process. As the yeast eats up the gooey parts of the fruit, acetic acid is formed. Not to worry, by the time the process is complete, there will only be teeny portions left within the bean.
However, roasting produces even more acetic acid by the further breakdown of carbohydrates and sugars.
Leaving us with a nice, balanced, velvety, yet crisp cup of coffee.
Troubleshooting: what to do if coffee tastes or feels too acidic?
Consider calcium
Even though popping a couple of TUMS after a meal sounds like the start to a bad dad joke, there is a truth in combating acid with calcium.
That’s why lattes and cappuccinos taste so much smoother than a shot of espresso.
To learn more about the complexities of espresso, check out my previous post here.
So if your brew has too much of a bite, add a little cream to the mix. Milks tend to land around 6.7 on the pH scale. The presence of any amount of milk will change the cup of coffee on a chemical level. By making this small adjustment, you bring a coffee from an acidic 5 on the pH scale closer to the palatable center balance.
Of course we also have an entire article dedicated to brewing lower acid coffee so there are plenty of options available to you without having to give up your morning brew.