A Thermomix® is a wonder weapon for chopping and mincing in the kitchen. So it's no surprise that many households also use the Thermomix® to chop coffee. This is basically possible, but it doesn't guarantee good coffee.
The Thermomix® is a chopping expert, but it grinds by cutting rather than milling. It's not equipped with grinding discs, but rather with blades that can achieve almost any particle size of coffee, vegetables, nuts, etc., depending on how long the blades run. Unfortunately, the precision of the Thermomix® is not sufficient for really good coffee. Additionally, the surface structure of a chopped coffee bean looks different from that of properly ground coffee.
The grind curve of coffee on an espresso grinder looks roughly like this. This level of grind precision cannot be reliably set with the Thermomix®. The coffee is chopped, but the grind varies from one grinding to the next, sometimes too fine, sometimes too coarse.
Why does coffee from the Thermomix® sometimes taste sour and sometimes bitter?
The changing taste is partly due to inconsistent particle distribution (variation in particle sizes). This varies from grinding to grinding because the blades don't always catch the coffee beans the same way. This is also because coffee has different densities depending on its origin. Additionally, bean sizes vary by variety, cultivar, and growing region.
Due to the cutting and chopping, the spread of particles is relatively large. This is relevant because finer particles tend to over-extract. This leads to bitterness in the coffee. Coarser particles are not dissolved as well by the brewing water. This leads to so-called under-extraction and thus to a sour-aggressive taste in your cup.
When 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?
It's not that simple to say. There are some very satisfied users who successfully use the Thermomix® for brewing filter coffee. If you know your Thermomix® well and use good coffee, you have a huge advantage over coffee from the supermarket. Pre-ground supermarket coffee has often already lost quality.
Coffee chopped in 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 quite as crucial for filter coffee as it is for espresso. With filter coffee, you can control the contact time between coffee and water in ways other than just adjusting the grind.
Espresso with the Thermomix®?
With espresso, the precision of the grind is very important. This is hard to achieve with the Thermomix®. But there's a trick here too! For once, the so-called "double-wall baskets" make sense. These are included with cheaper espresso machines. The baskets themselves have only a small opening through which all the coffee is forced. This is how the baskets build up the resistance that cannot be created by pre-ground coffee powder.
A good espresso has a brewing time of approximately 20-30 seconds. With the double-wall basket, this time is achieved with almost any coarser ground coffee or even older coffee. If we now use the Thermomix® and don't grind too fine, we can use the double-wall basket. This gives us a good extraction time. The espresso won't be as perfect as with a properly adjusted espresso grinder, but the result will be good, corresponding to the coffee used.
