Check that no grounds have been left to collect on any part of the equipment and that there is no build - up of coffee oil. (konacoffeebelt.com)
If I use hot coffee the oil melts but is the smoothie now so warm that it defeats the nutrition benefit of a raw egg yolk? (livingthenourishedlife.com)
These days this technique usually employs methylene chloride (used predominately in Europe), coffee oil or ethyl acetate to dissolve the caffeine and extract it from the coffee. (scientificamerican.com)