A Thermomix® is a miracle weapon for chopping and mincing in the kitchen. Therefore, it is no surprise that many households also use the Thermomix® to grind coffee. While this is fundamentally possible, it does not guarantee good coffee.
The Thermomix® is a master at chopping, but it does not grind—it cuts. It is not equipped with grinding discs, but with blades that can achieve almost any grain size for coffee, vegetables, nuts, etc., depending on the duration of the cutting time. Unfortunately, the precision is not sufficient for truly good coffee. Furthermore, the surface structure of a crushed coffee bean looks different from the surface of ground coffee.
The grinding curve of coffee in an espresso grinder looks roughly like this. This precision of the grind size cannot be reliably set with the Thermomix®. The coffee is indeed chopped, but the consistency varies from one grind to the next.
Why does coffee from the Thermomix® sometimes taste sour, sometimes bitter?
The changing taste is partly due to the inconsistent particle distribution (number of grain sizes). This varies from grind to grind because the blades do not always catch the coffee beans in the same way. This is also because coffee has a different density depending on its origin. Additionally, bean size varies by variety, cultivar, and cultivation region.
Due to the cutting and chopping process, the particle dispersion is relatively large. This is relevant because finer particles tend to over-extract. This leads to bitterness in the coffee. Coarser particles cannot be as easily extracted by the brewing water. This leads to so-called under-extraction and thus to a sour, aggressive taste in the cup.
If both fine and coarse particles are present, this results in a mixture of bitterness and acidity that tastes particularly unpleasant.
Is a Thermomix® not suitable for any coffee?
That cannot be said so generally. There are some very satisfied users who successfully use the Thermomix® for brewing filter coffee. Anyone who knows their Thermomix® well and uses good coffee has a huge advantage over supermarket coffee, which is often pre-ground and has already lost quality.
Coffee chopped with a Thermomix® is always better than pre-ground coffee from the supermarket!
However, we recommend using Thermomix®-chopped coffee for filter coffee. The precision of the particles is not as critical for filter coffee as it is for espresso. With filter coffee, the contact time between coffee and water can be controlled in ways other than just the grind size.
Espresso with the Thermomix®?
For espresso, the precision of the grind size is extremely important. This is almost impossible to achieve with the Thermomix®. However, there is a trick here too! For once, the so-called "pressurized baskets" make sense. These are often included with cheaper espresso machines. The baskets themselves have only a small outlet through which all the coffee grounds are squeezed. This allows the baskets to build the resistance that cannot be built by the grounds themselves.
A good espresso has a brewing time of approx. 20 - 30 seconds. Through the pressurized basket, this is achieved with almost any coarser ground or even older coffee. If we now use the Thermomix and do not grind too finely, we can use the pressurized basket. This gives us a good extraction time. The espresso is not as perfect as it would be with a properly adjusted espresso grinder, but the result is good relative to the coffee used.
