TDS in Coffee: Brewing and Extraction

What is TDS?


As most of you must be aware of the full form, TDS is Total Dissolved Solids. TDS is the measure of the dissolved content present in a liquid in a suspended form. With coffees, generally, TDS has different implications with:


1. Brewing coffee (as a measure of dissolved solids in the water used)

2. Brewed coffee (as a measure of the extraction of coffee)


Let's start.


(If you're interested in the results and parameters to be maintained, scroll to the end of the article.)



"Your cup of coffee contains 98% water"



TDS in brewing coffee is a factor of the "Dissolved Solids in your Source Water", i.e. the water that we use to brew coffee. Since your cup of coffee is mostly water, we need to ensure that we're using is the water which essentially "tastes well".


In addition to that, the dissolved solids which include minerals, salts and some solids, directly contribute to the coffee extractions. The amount and the type of these solvents will affect the way your cup of coffee tastes like. Let's explain this in very easy words.


Your source water has a carrying capacity, let's refer this to as "100 X". This 100 X is to be shared between "The solvents in the Source Water" and "The Coffee to be absorbed from the Ground Coffee".


If the solvents in the Source Water are low (low TDS water), let's say equivalent to 15 X, the water will have 100 X- 15 X= 85 X available for absorbing coffee grounds. More than the required percentage of coffee is absorbed while using low TDS water.


"Less TDS in source water, More extraction"


If the solvents in the Source Water are high (high TDS water), let's assume 75 X, the water will have 100 X-75 X= 25 X available for absorbing coffee grounds. Lesser than ideal required percentage of coffee is absorbed while using high TDS water.


"More TDS in source water, Less extraction."


"With source water, we measure the TDS to optimize our extractions. With brewed coffee, we use TDS as a reference point and optimize our brewing techniques."


To satisfy the geek within you, different equipment extract differently. Let's provide you with some optimal TDS figures (source Fellow products):


Pour-Over: 1.2-1.5

AeroPress® Coffee Maker: 1.4-1.7

French Press: 1.4-1.7

Fellow Prismo: 3.5-5

Espresso: 8-12


To sum up the above statements:

  1. Your source water directly affects the initial flavor of your cup.

  2. Your source water directly affects the extraction process. More TDS under-extracts while Less TDS over-extracts.



Let's talk equipment.



To measure the TDS of your source water, the electronic equipment used is called a TDS meter. The TDS meter contains sensors which measure the electric conductivity (EC) for water. EC is a function of a TDS and Temperature of the water. The TDS Meter is a relatively inexpensive equipment (3-5 USD).


To measure the TDS of your brewed coffee, we use a refractometer. To understand it in very simple words, light bends from one medium to other. The more the number of dissolved particles (i.e. more extraction), the more the light will bend in a refractometer. Unlike the TDS Meter, the refractometer, is an expensive piece of equipment (200-1000 USD).



Finally, let's talk Parameters.


"With source water, we measure the TDS to optimize our extractions. With brewed coffee, we use TDS as a reference point and optimize our brewing techniques."


Source Water


Now that we've established that neither Low nor High TDS is favorable for brewing coffee, we need to tell you the sweet spot of your Source Water. The SCAA specifies a TDS level of 75-250 ppm for Source Water, with an ideal target of 150 ppm.



TDS levels for equipment:


Pour-Over: 1.2-1.5

AeroPress® Coffee Maker: 1.4-1.7

French Press: 1.4-1.7

Fellow Prismo: 3.5-5

Espresso: 8-12



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