Coffee TDS measurement with SmartRef Digital Refractometer
Jul 20, 2023
A little coffee story … about the SmartRef coffee refractometer and TDS coffee measurement
Almost everyone knows it, many love it, some just can't live without it - coffee
For many people, drinking and enjoying coffee is part of their daily routine. Some like it very strong, others prefer it weak and mild. But what does strong or weak coffee mean?
Usually, it can be said that espresso tastes stronger than filter coffee. But taste is rather subjective and varies from person to person. To rule out subjective opinions and to be able to describe the strength of coffee objectively, the scientific aspect has gained influence in recent years.
Let's talk about total dissolved solids (TDS) in coffee - or the strength of your coffee
Only 30 % of the coffee bean is soluble, the other 70 % consists of insoluble fiber and carbohydrates, which are responsible for the structure of the bean.
With a TDS coffee refractometer, you are able to measure the strength of the coffee, the TDS value.
The TDS value describes the amount of the total dissolved solids in a sample in percent. Simply put, it describes how much of the coffee bean has been dissolved into your coffee and how concentrated (strong) or watery (weak) the coffee is. A stronger-tasting coffee, e.g. espresso, will have a higher TDS, while a weaker coffee, e.g. filter coffee, will have a low TDS.
This makes it possible not only to speak subjectively about the strength of the coffee, but also to make the taste measurable.
Typical TDS values for different coffees
- Ristretto: > 12 % TDS
- Espresso: 8 – 12 % TDS
- Lungo: 2 – 8 % TDS
- French press: 1.4 – 1.7 % TDS
- Filter coffee: 1.2 – 1.5 % TDS
TDS can give roasters, baristas, and coffee lovers a valuable insight into the solubility of a roast, e.g. the darker the roast, the more solubles in the bean are present, and the lighter the roast, the less solubles are present. With this in mind, you might do shorter extractions with a finer grind for a dark roast and longer extractions with a medium-coarse grind for a lighter roast.
Additionally, TDS can help to determine the equipment setup and ensure consistent brew extraction throughout the day.
From coffee TDS to coffee extraction
In the world of coffee making, there are two very important numbers: Total Dissolved Solids (TDS) and Extraction Percentage.
Once you know the TDS, you can use a simple equation to determine coffee extraction:
- Extraction percentage: how much of the dry coffee is dissolved in the water you used to brew your coffee in percent
- Brewed coffee: how much liquid you have in your cup after brewing
- Ground coffee: the amount of dry coffee you weighed in
Why do we need the extraction value?
Some flavors, such as the sour and fruity notes, are extracted first because they can quickly dissolve in water. The oils and sugars follow as they take a little longer to come out. Bitterness takes the longest to extract.
Lower extraction results in "lighter" flavors like citrus, tea or flowers, higher extraction results in "deeper" flavors like caramel or chocolate, depending on the coffee. Basically, one can say that the optimal extraction yield is between 18-22 %. Values below 18 % are considered under-extracted, resulting in a sour taste, values above 22 % are considered over-extracted, resulting in bitter coffee. However, the optimum extraction range depends on the country of origin of the coffee, the roast, the grinder or the brewing method and can vary with different types of coffee.
How can I change the TDS value for my perfect coffee?
If you make your own coffee at home, the strength of your coffee may vary from brew to brew. In order to have a coffee that always tastes the same, it is necessary to consider that several factors can change the strength of your coffee:
- Change the water/coffee ratio: the more coffee you use with the same amount of water, the stronger the coffee will be
- Change the grind of your coffee: the finer the coffee is ground, the larger the surface area; more coffee gets extracted resulting in a stronger coffee
- Change the temperature of your brewing water: the hotter the water, the more efficient the extraction
- Change brewing time, brewing type or roasting type
- Stir your coffee when making filter coffee to homogenize your brew
Experiment by adjusting one factor at a time. Measure the TDS value during the changeover and check which settings and changes bring you the best coffee! By understanding extraction and other influencing factors, you can make better coffee.
How do we measure TDS with SmartRef Digital Refractometer?
- Clean your SmartRef before use.
- Adjust SmartRef with distilled water (not required before each measurement).
- Stir your coffee sample thoroughly (as the coffee settles very quickly).
- Pipette the hot coffee with a syringe and allow it to cool to room temperature in the syringe before pouring the coffee onto the refractometer.
SmartRef tip: To minimize evaporation during the cool down period, cap the syringe with a tip cap. When the coffee has cooled, shake your syringe before measurement to ensure homogeneity.
- Pipette coffee into the sample well until the marked height.
- Start your measurement (% TDS) with the Lab Meister App, the result will be displayed within seconds.
- After measurement, clean your SmartRef by rinsing it with water and wipe it dry with a clean towel.
As you can see, there are many factors to consider to brew the perfect coffee. Don't give up and find out which mixture and preparation suits you best.
SmartRef is your perfect companion that will reliably support you in your brewing experiments.