Alkalinity is one of the most useful water variables to experiment with.
It is closely related to the water's capacity to neutralise acids.
Coffee contains acids.
So changing alkalinity can change how those acids are perceived.
The experiment
Prepare two waters.
Water A:
lower alkalinity
Water B:
higher alkalinity
Keep the hardness and other major variables as similar as practical.
The goal is to isolate buffering as much as possible.
Choose a coffee with clear acidity
A washed high-altitude coffee can be particularly interesting.
Look for:
citrus
malic acidity
floral notes
or a bright fruit profile.
The clearer the acidity, the easier it may be to notice a change.
Keep everything else constant
Same:
coffee
dose
grind
temperature
ratio
brewer
pouring
brew time
Only the water changes.
What might you expect?
Lower alkalinity may allow acidity to appear more prominently.
The coffee may feel:
brighter
sharper
more sparkling
or more transparent.
Higher alkalinity may soften the perceived acidity.
The coffee may feel:
rounder
softer
less sharp
or potentially flatter.
But these are hypotheses.
Taste decides.
Too much buffering
If alkalinity becomes excessive for the coffee, acidity can lose definition.
A coffee that originally tasted like:
lemon
bergamot
and white grape
might become less distinct.
The flavours haven't necessarily disappeared.
Their perception has changed.
Too little buffering
At the other extreme, very low alkalinity may make some coffees feel excessively sharp.
A coffee can have beautiful acidity and still become unpleasant if the balance is wrong.
This is why:
low alkalinity = better
is just as simplistic as:
high alkalinity = better.
Why this experiment is useful
Unlike TDS, alkalinity has a clear conceptual relationship with acid-neutralising capacity.
That makes it a useful variable to isolate.
You can learn something directly about the role of buffering in the cup.
Repeat with another coffee
After the first experiment, try a coffee with:
lower perceived acidity
or
a more developed roast.
The result may be different.
This helps demonstrate that water interacts with the coffee rather than acting independently.
Record the result
Write down:
water alkalinity
hardness
TDS
coffee
brew recipe
sensory notes.
If possible, taste blind.
The Water Artist
We don't want a universal alkalinity number.
We want to understand the relationship between:
coffee acidity
and
water buffering.
That's more useful.
The question
Don't ask:
"What alkalinity is best?"
Ask:
"How much buffering does this coffee need?"
Water is the canvas.
You're the artist.