There is special part of the colon called the sigmoid colon, which is just before the colon. There are a group of veins at this point that connect directly to the liver; it is called the enterohepatic circulation. It function is to remove highly toxic material directly to the liver where there can be safely treated rather than have enter the bloodstream.
With a coffee enema the caffeine is absorbed by the enterocirculation veins and goes to liver. This immediately causes the liver to produce bile which has liver toxins connected. The bile is used as a carrier for the toxins. This detoxification flush appears to free up the liver to process toxic material from other parts of the body.
Hopefully Iíve got this next bit correct.
Coffee plants contain two different kinds of a substance called an alkaloids which act on the body like a drug. One category is called purine alkaloids includes caffeine, which is well known and theobromine and the other is the category pyridine alkaloid, called trigonelline. Generally speaking trigonelline is only found in coffee.
These alkaloids and trigonelline is often quoted as the main active ingredient, causes an enzyme called glutathione-S-transferase to be produced. It is this enzyme that causes to liver to go into a detoxification mode. This alkaloid is also found in the herb fenugreek.
Because a coffee enema has the potential to increase bile then it is also possible that this may result in the elimination of liver congestion; even stones.