Regardless of the opinions and arguments, I think the reason these drinks help the digestive process is because they are all high-proof liquor. Italian moonshine. The smell alone could wake the dead. The liquid heat upon swallowing is so intense, it is felt all the way down. Literally.
(Drinking grappa also makes you make funny faces.) My theory for why grappa works so well is this: after ingesting the digestivo, it creates a small blaze in the stomach, which consumes all the food. Then the GI tract has nothing to worry about. Travelers hint: always carry chewable Rolaids.
I am returning to the land I love in less than two weeks and my quest for a tasty digestivo will continue. My Italian friends are convinced that, with their help, I will find the digestivo of my dreams. And I will discreetly report my personal results.