70/30 water
A controlled solvent for coffee brewing.
70/30 water is proposed as a starting point for experimentation in controlled brewing. It is designed to be
prepared from readily available materials. A water preparation procedure could be useful for cupping coffee under
more standard conditions and a procedure for the controlled mineralisation of brew water is a starting point for
further experimentation.
The name ‘70/30’ is derived from the concentrations of bicarbonate and magnesium in the finished water. These
concentrations are suggested based on guidelines published by the SCAA, presentations by Colonna-Dashwood
and sensory evaluations conducted at Five Senses Coffee. This water is not suggested as perfect brew water, but
as a step towards controlling water quality based on what is known so far.
The following text describes the preparation of this water with easily available materials and equipment. It really is
very easy – easier than making coffee.
Low TDS Water • To begin with, you will need water
with a low TDS. If you have access to a reverse osmosis
unit, the water this produces would be a good start.
Distilled water will be even cleaner. Failing this, read
the nutritional information panel on bottled water at
the supermarket and choose the one with the lowest
numbers for whatever is listed (sodium, calcium and
bicarbonate are likely ingredients.)
Bicarbonate • added in the form of sodium
bicarbonate, this is easily obtained as a raising agent for
baking; it might be labelled as ‘bicarbonate of soda’.
Magnesium • most easily obtained as Epsom salts,
which are magnesium sulphate. I’ve found it easy to find
in supermarkets and pharmacies.
How to prepare stock solutions
The aim is to get around a few hundredths of a gram of
each of these substances into a litre of water. Because
you probably don’t have a set of scales which will weigh
out five hundredths of a gram (or even half a gram), we
will use a stock solution to make the quantities easier
to handle.
Sodium Bicarbonate stock solution • Weigh out 14g
of sodium bicarbonate into a measuring jug. Top the
jug up to 1000 ml with low TDS water and stir until
dissolved. Store this in a sealed bottle to limit contact
with surrounding air.
Magnesium Sulphate stock solution • Weigh out 12g of
Epsom salts into a measuring jug. Top up to 1000 ml
and dissolve as per the sodium bicarbonate solution.
Using the solutions to make brew water
Simply add 1 metric teaspoon (5 ml) of each of these to
a litre of low TDS water to make your final brew water.
This water will then be approximately 70 ppm of sodium
bicarbonate and 30 ppm of magnesium sulphate.
If you want to experiment with changing these
concentrations, a graduated syringe is the cheapest
way get millilitre accuracy.
Some notes on units
You will notice that the concentrations of these water
additives are usually measured in ppm (parts per
million), which is the same as milligrams per litre. The
confusing thing is that this doesn’t always refer to
milligrams of what is actually in solution. For example,
hardness is usually measured in ppm of calcium
carbonate. It is assumed that the hardness is made up
of calcium carbonate, but it might actually be made
up of magnesium carbonate, or even other forms
of magnesium and carbonate. The same applies to
alkalinity. It can get quite complicated.
My advice is not to get too bogged down in this. For
our purposes, units should refer to what is actually
in the water, but you might want to bear the other
complexities in mind when looking at measurements of
your local water quality or at SCAA guidelines.
With that in mind, these instructions
will produce water that is:
70 ppm NaHCO3 and 30 ppm MgSO4
42 ppm total alkalinity
25 ppm hardness as calcium carbonate
50 ppm bicarbonate ion
6 ppm Mg2+ ion
For a comparison with what might be coming out
of your tap, the total alkalinity for our water here in
Perth ranges from around 30 to 180 ppm (as calcium
carbonate), while hardness ranges from around 30 to
230 ppm. Your local water authority should have similar
figures readily available.
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