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“Here’s my super simple and not 100% accurate defini- You could measure your water TDS by evaporating the
tion: Extraction is everything that the water takes from the cof- water and weigh what’s left. Since this is nearly impossible to do
fee. When you mix coffee and water, a lot of things happen. The for the average person, you could use a TDS meter. This method
most relevant and easy to understand of all these things is that of analyzing water composition is to measure electrical conduc-
water dissolves a lot of coffee’s flavors. These dissolved flavors tivity and then estimating total dissolved solid (TDS) in water
make up almost everything you taste when you drink a cup of from this measurement. Using electrical conductivity or TDS to
coffee. The rest is undissolved stuff. This is mostly very very describe water properties is not a meaningful parameter on its
small coffee grinds that affect mouthfeel, but can’t be included own with regard to coffee extraction. This is because the conver-
in extraction because they’re just floating around in the water.” sion from electrical conductivity to TDS depends heavily on the
So, when we talk about extraction in coffee, it serves water composition and temperature, yielding results that can
as a medium for flavor. While brewing, water takes in—or ex- vary significantly. Additionally, even if the estimated TDS value
tracts—solids & oils that coffee holds, giving that once cleared is accurate, it does not contain any information on what the TDS
water some real substances. The final result is coffee. Water has is actually made up of. In other words, using a TDS meter does
all sorts of trace amounts of minerals in it, giving both flavor and not tell you exactly what is the mineral content in your water, it
extracting ability. There are several minerals that can be found in only tells you how much solids are in your water.
water but the most important minerals that are relevant in coffee
extractions are Calcium (Ca), Magnesium (Mg), and Bicarbonate
(HCO3). Now let’s take a look at what each of these minerals af-
fects the espresso machine and taste.

Christopher H. Hendon, Authors of “Water for Coffee”

Hendon stated “TDS is not a good measurement because
it is a collective measurement of ions. We care about the nature
and identity. High pH is usually an indication of high bicarbonate
concentration so that is not always good. High hardness is also
an indication of high bicarbonate. But again, you need to titrate
to test for each ion.” Water with high alkalinity can result in dull
and flat coffee. Acidic water creates bright, imbalanced and/or
TDS meter unrefined coffee.

Measuring Water How to get the most accurate reading
When it comes to brewing coffee, it’s important to un- Shake: Always make sure to shake excess water off the
derstand that the more mineral content water has, the less it can meter before dipping it into a water sample, even
take in from coffee. Some minerality is good, too much is bad. The if it's the same water.
mineral content of water including minerals, salts or metals, is Stir/tap: After dipping the meter in the water, always
expressed as the Total Dissolved Solids (TDS), expressed in units lightly tap it against the side and stir the meter
of mg per unit volume of water (mg/L), also referred to as parts to remove any lingering air bubbles or electrical
per million (ppm). The TDS range of a particular city’s tap water charges.
can range anywhere from the 10’s to 100’s, depending on the loca- Positioning: When taking the reading, always make sure to
tion and water treatment process. Ideal water for coffee has a TDS hold the meter straight up without it touching
of 90-150 ppm, with no extraneous odors or flavors that would the sides or bottom of the glass/beaker/cup.
interfere with taste, but still has enough TDS that the minerals in The probes should be suspended as close to the
the coffee are able to help do the work of extraction. center of the water sample as possible.
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