1. Roots need to be brewed the longest amount of time due to their density. They contain the highest amount of minerals.
  2. In order of required brewing time, after roots, bark needs the most followed by twigs, leaves and flowers.
  3. Leaves contain the most vitamins. Since vitamins are lost during the heating process, infusion, which requires less cooking, retains more nutrients in herbal preparations.
  4. Flowers contain volatile oils that are dispersed when decocted. Therefore, they should either be gently infused or placed in a medicinal combination and only decocted during the last few minutes of the process, if you are trying to conserve the volatile oils.

I was also taught that taking an alcohol-based tincture drives the herb(s) to the liver for breakdown with less herb available to move through the digestive tract. And that drinking a decoction drives the herb(s) to the kidneys and through the digestive tract.