Add entire four ounce bag of chaga chunks to one gallon of water, bring to a boil. Lower heat to a light boil with a lid for two hours. Turn off and let cool.
Secure damp cheese cloth to the tops of three mason jars with rubber bands, and pour the cooled chaga into the jars (see picture below).
Keep the jars of chaga in the refrigerator, they will last up to a month. Drink eight to twelve ounces a day.
Store the chunks of chaga in the freezer, the chunks can be boiled three times at one gallon per boil.