Calcium and magnesium are often grouped together because both contribute to water hardness.
But grouping them together doesn't mean they behave identically.
A controlled comparison can help reveal what changes when the balance between them changes.
The experiment
Prepare two waters.
Water A:
magnesium-forward
Water B:
calcium-forward
Try to keep other variables as similar as practical.
For example:
similar overall mineralisation
similar alkalinity
same base water
same brewing recipe.
Why not simply compare hardness?
Because hardness alone hides the composition.
Two waters can have similar hardness while containing different amounts of calcium and magnesium.
The purpose of this experiment is to expose that difference.
Brew the same coffee
Choose a coffee with a clear sensory profile.
A washed coffee can be useful because subtle changes in acidity and aroma may be easier to observe.
But a natural coffee can also be interesting.
The key is consistency.
Taste blind
Look for:
aroma intensity
acidity
sweetness
body
clarity
bitterness
finish
balance
Don't decide what should happen before tasting.
What does research tell us?
The coffee-water literature provides reasons to expect calcium and magnesium to behave differently.
The 2014 Hendon work proposed strong interactions between magnesium and certain coffee compounds.
More recent experimental research has shown that the practical effects of calcium and magnesium at typical concentrations can be more limited and complex than simple extraction narratives suggest.
That makes sensory testing especially valuable.
Don't turn the result into a universal rule
Suppose magnesium-forward water wins your tasting.
That doesn't prove magnesium is better.
It means:
"This coffee, under these conditions, produced a preferred result with this profile."
Change the coffee and the answer may change.
Repeat with another roast
Try:
light roast
medium-light roast
different processing
different origin.
Now you can ask whether the pattern repeats.
The real value
The experiment teaches you to stop thinking of calcium and magnesium as:
good mineral
versus
bad mineral.
Instead, they become variables.
Variables can be tested.
The Water Artist
The question isn't:
"Which mineral is best?"
It's:
"What happens when I change the balance?"
That is a much more useful question.
Water is the canvas.
You're the artist.