I may now say that my intuition was not wrong, coffee is a great stuff, it will be preserved in the next experiences.
I accepted the suggestion of the commenter ErikP and made a soup only with soda and Tetenal developer, leaving coffee apart. The results are a disaster. Only a mix of color dyes and no clear image definition. Yes, there may be other reasons for that and I simply can't see. Waiting comments!
The negative is dark and more red:
Positivation with GIMP gives bright colors.
Observations: One could expect, according to the theory, a better negative with more colour and definition. The reality shows that the approach with coffee and only 30 ml Tetenal is better. I am now thinking what will be the next try. Maybe reduce coffee quantity and increase Tetenal to let us say only 45 ml. Because the shift to red is good, but there was a lost of definition.