What does coffee acidity mean?

One of the questions I am asked about coffee from time to time is to do with acidity. Usually people wanting to know which is the least acidic coffee we do as they have concerns about their diet, or health.

There is, justifiably, some confusion, due to the fact that there are two sorts of acidity when it comes to coffee!

Most of us are familiar with acids and alkali as being a chemical measurement using the pH scale. Ok so here is a schoolboy explanation, not trying to be patronising of course!

The scale goes from 0 to 14. Low numbers are acid, high numbers are alkali. So, at zero we have battery acid, and at 14 we have drain cleaner.

Neutral is 7 and our blood is 7.4, so slightly alkali

Black coffee (of all sorts) is 5 and milk is 6.3 (as is urine by the way), so slightly acid.

Lemons are about 2.

ACID to ALKALI

0 - battery acid

2- lemons

5 - black coffee

6.3 - milk, urine

7 NEUTRAL

7.4 - human blood

9 - baking soda

14 - Drain cleaner

So, all black coffee is actually around pH5, The WORD acidity in coffee is more about sensation and less about the science.

The taste may be described as acidy tasting, like citrus fruit, or ‘sharp’, but these are mouthfeel descriptions. So why do they call it ‘acid’ and how can one coffee taste more or less acid than another if there is no chemical scale involved?

There are things which change the perception of acidity and they range from the plant to the brewing method used. Here are a few of the things that will affect the final ‘acidity’ in coffee terms.

Below I've listed what can affect the acidity:

1. Arabica beans are said to be better the higher above sea level they are grown, and achieve a better ‘balance’ of acidity, but they are less acid if they come from lower heights, so a low grown arabica will be less acid than a higher grown one, but not as highly prized!


2. During the roasting process there are lots (hundreds I am reliably informed) of chemical changes going on inside each bean and as a roaster you seek to make the best outcome for each type of bean which is called profiling (I’m really trying not to be a know it all, or patronising-it’s a tough call, bear with me) As the roast gets darker, the acidity decreases and the sweetness increases, take it a touch too much and it turns to bitter then sour in an instant (no pun intended).


3. For some unfathomable reason, the finer you grind coffee for an espresso, the lower the acidity. If it tastes bitter it will taste the least acidic, which is why some people prefer a bitter espresso.

Nothing is simple. If it is just a chemical question, then there isn't much discernible difference, it’s 5, as I said at the top, but to answer the question, ‘Which is the least acidic (tasting) coffee you sell?’ the short answer is…. Ethiopian Limu, made in a cafetiere! (although there may be others-told you it wasn’t simple!)