A Thermomix® is a miracle weapon for reducing and chopping in the kitchen. Therefore, it is not surprising that coffee is also ground in many households with the Thermomix®. This is fundamentally possible, but does not guarantee good coffee.
The Thermomix® is a chopping artist, but it doesn't grind, it cuts. It is not equipped with grinding burrs but with blades that can achieve almost any particle size of coffee, vegetables, nuts, etc., depending on the chopping time. Unfortunately, for coffee, the precision for really good coffee is not sufficient. In addition, the surface structure of a crushed coffee bean looks different from the surface of a ground coffee product.
The grinding curve for coffee looks approximately like this with an espresso grinder. This precision of the grind cannot be reliably set with the Thermomix®. The coffee is crushed, but varies in fineness or coarseness from grind to grind.
Why does coffee from the Thermomix® sometimes taste sour, sometimes bitter?
The changing taste is partly due to the inconsistent particle distribution (number of particle sizes). This varies from grind to grind, as the blades do not always process the coffee beans in the same way. This is also because coffee has different densities depending on its origin. The size of the beans also varies depending on the variety, type, and growing region.
Due to the cutting and crushing, the particle distribution is relatively wide. This is relevant because finer particles tend to over-extract. This leads to bitterness in the coffee. Coarser particles cannot be extracted as well by the brewing water. This leads to what is known as under-extraction and thus to a sour-aggressive taste in the cup.
If both fine and coarse particles are present, this leads to a mixture of bitterness and acidity that tastes particularly unpleasant.
Is a Thermomix® not suitable for any coffee?
This cannot be said across the board. 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. This is often pre-ground and has already lost quality.
Coffee chopped with the 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 crucial for filter coffee as it is for espresso. With filter coffee, the contact time between coffee and water can be controlled differently than just by the grind size.
Espresso with the Thermomix®?
For espresso, the precision of the grind is very important. This is almost impossible to achieve with the Thermomix®. However, there is a trick here too! For once, the so-called "dual-wall baskets" make sense. These are included with cheaper espresso machines. The baskets themselves have only a small outlet through which all the coffee grounds are squeezed. This is how the baskets build up the resistance that cannot be built up by pre-ground coffee.
A good espresso has a brewing time of approx. 20 - 30 seconds. This is achieved with almost any coarser ground coffee or even older coffee through the dual-wall basket. If we now use the Thermomix and do not grind too finely, we can use the dual-wall basket. This gives us a good extraction time. The espresso is not as perfect as with a precisely set espresso grinder, but the result is good in accordance with the coffee used.
