Digeestive bitters are usually made out of herbs...bitter herbs. Look at the label on the Swedish Bitter or other brands at the health food store to get an idea of what herbs they use. You could potentially use a very bitter food, though getting an herb would be better. The trick is, the bitter has to come in contact with your tongue and sit there a while in order to stimulate the needed response in your body. So make a strong tea, take a good sized sip and hold it in your mouth, swish around, then swallow. Do this for the whole cup, sip by sip, about 20 minutes before you eat. Dandelion is a digestive bitter and you should be able to find it growing outdoors still this time of year, and, this time of year the leaves will definitely be bitter! You can also use wild mustard greens (the greens in the store are milder), and wintercress is a possibility if it grows in any streams near you.