I am brazilian, therefore I am addicted to coffee. OK, not all brazilians drink coffee, as not all US Americans play baseball. This does not change the fact that I feel miserable if I have to go out my home in the morning without drinking a large mug of the dark brew (which I drink without additions, including sugar).
I also travel a lot, occasionaly going to places in which coffee is decisively horrible. Recently a former student went through the same problem, and this reminded me of the period in which I lived in Germany.
Not that German coffee is that bad, at least there are places in the world in which coffee is even worse. The problem with German coffee is that if you drink it using a glass, you can see through! For me, this was something like an heresy.
Being myself a scientist, I decided to make experiments. Soon I discovered that the amount of powder didn’t matter. Neither did the roasting level. I tried powders of various provenances, but this didn’t help either.
Then, one day, I was buying coffee powder at a specialized shop called Tschibo (I had already partially solved my problem, noticing that freshly ground coffee produced better results) when the vendor asked me wether I wanted my powder fein gemahlen (finely ground) or grob gemahlen (coarsely ground). I asked her what was the difference and she explained to me that the finely ground particles were designed for expresso machines and that if I used it with normal filter, I would get particles going through.
Imediately I realized the solution to my problem, I asked my powder finely ground and confirmed the next day that I was able to brew Brazilian quality coffee in Germany.
My explanation is the following: in Brazil the griding machines are old, the filters are bad, so many fine particles pass, giving the excellent taste we are used to. In Germany the machines are brand new, the filters are perfect, and hence, only liquid passes. Naturally, having solid particles in suspension the Brazilian coffee becomes opaque.
Of course, according to the scientific method, I would need to further test my hypothesis. I would need to perform a granulometric analysis of the different powders, or verify the solid residues left from evaporation. As my good friend, Eng. Alberto Imoto thaught me, however, in the case of performance-driven research you are entitled to stop the action once you get the desired effect.