Perception vs Chemistry in Coffee
pH is often treated as the definitive way to understand acidity in coffee. It’s measurable, objective, and widely used across the industry. If a coffee has a low pH, it is considered more acidic. If the pH is higher, it is considered less so.
But in practice, this way of thinking quickly breaks down.
Because while pH tells us how acidic a liquid is from a chemical standpoint, it does not reliably tell us how acidic that coffee will taste. And in coffee, what matters most is not the chemistry in isolation, but how that chemistry is perceived.
To understand this, we need to separate two ideas that are often confused: chemical acidity and perceived acidity.
What pH actually measures
pH measures the concentration of hydrogen ions (H⁺) in a solution. The more hydrogen ions present, the lower the pH, and the more chemically acidic the liquid is.
This is a precise and useful measurement. In coffee, the organic acids naturally present in the beans contribute to this pool of hydrogen ions, and pH gives us a snapshot of that chemical reality.
But tasting coffee is not the same as measuring it.
Acidity is a sensory experience
When we drink coffee, we don’t perceive hydrogen ions directly. What we experience instead is a combination of brightness, sharpness, sweetness, structure, and balance.
This is what we refer to as perceived acidity.
Perceived acidity is not determined by pH alone. It is shaped by how different elements in the cup interact with one another, and how those interactions are interpreted by our sensory system.
A simple example: Coca-Cola
Coca-Cola has a pH of around 2.5, making it significantly more acidic than most coffees, which typically range between pH 4.5 and 5.5.
From a chemical perspective, Coca-Cola is far more acidic.
Yet it does not taste aggressively acidic.
The reason is the high sugar content. Sweetness balances and suppresses the perception of acidity, changing how the brain interprets the overall flavour. The chemical acidity remains the same, but the experience is completely different.
This is a clear example of how pH and perception can diverge.
Water is not just H₂O
When we brew coffee, water contains dissolved minerals in the form of ions — charged particles that influence how flavour is perceived.
Common ions in brewing include magnesium, calcium, sodium, chloride, sulfate, and bicarbonate. Each of these plays a different role in shaping the cup.
Some of them affect pH directly. Others do not, but still have a significant impact on how acidity is experienced.
Which ions actually change pH
Among the ions commonly used in coffee, bicarbonate is the most relevant when it comes to pH.
Bicarbonate acts as a buffer. It neutralises hydrogen ions, reducing chemical acidity and increasing pH. Increasing bicarbonate content will therefore make a coffee less acidic from a chemical standpoint.
In contrast, most other ions used in brewing — including magnesium, calcium, sodium, chloride, and sulfate — do not significantly alter pH. They are not strong acids or bases.
Their influence lies elsewhere.
Magnesium and the expression of acidity
Magnesium plays a key role in how acidity is perceived.
Coffees brewed with magnesium-rich water tend to feel brighter, more defined, and more expressive. Acidity becomes easier to identify and more clearly articulated.
This does not necessarily mean that there is more acid in the cup, or that the pH has dropped. Instead, magnesium improves clarity and separation between flavour components, allowing acidity to stand out more distinctly.
In simple terms, magnesium does not increase acidity. It reveals it.
When chemistry and perception move in opposite directions
This is where things become particularly interesting.
At APAX, we see this clearly with the TONIK profile.
TONIK contains bicarbonate, which technically raises pH and reduces chemical acidity. From a purely analytical perspective, you would expect the coffee to taste less acidic.
At the same time, TONIK is high in magnesium (and sodium), which enhances clarity, structure, and sweetness, allowing acidity to become more expressive and better defined.
The result is a profile where:
- pH increases
- chemical acidity decreases
- but perceived acidity increases
This is a direct example of how relying on pH alone can lead to the wrong conclusion about how a coffee will taste.
Why pH alone is not enough
Two coffees can have the same pH and taste completely different in terms of acidity. One may feel bright and vibrant, the other flat and muted.
Likewise, two coffees with different pH values can feel similar in perceived acidity, depending on how other elements interact.
pH measures one variable. Perception is the result of many.
Designing acidity with intention
If the goal is to control acidity in coffee, it’s important to distinguish between:
- chemical control (adjusting pH through buffering)
- sensory control (shaping how acidity is expressed)
Bicarbonate allows you to reduce acidity chemically by increasing pH.
Magnesium allows you to shape how that acidity is perceived, making it more or less visible in the cup.
Understanding this distinction is what turns water from a fixed parameter into a design tool.
Closing thought
pH is a useful measurement, but it does not define the experience of acidity.
Acidity in coffee is not just about how much acid is present. It is about how that acidity is expressed, balanced, and perceived.
If you want to truly understand coffee, you have to move beyond numbers and start thinking in terms of flavour.
