I am in the middle of reading a long piece in Tehumin 31 on this topic. I’ll follow up when I finish.
In the meantime, bal teshaktzu is definitely a player here, but the coffee is unlikely to be forbidden because of this. The coffee bean looks normal, and certainly the coffee is not mi’us, on the contrary, it is supposed to be splendid. The disgusting aspect is only in the preparation and not in the product. The coffee drinker is not exposed to anything that would be considered m’shukatz, and based on this specific consideration, there is no issur bal teshaktzu and the coffee is permitted