Refreshing Non-Alcoholic Ginger Beer
Brewer's yeast is available from home brewing stores. Don't use bread yeast with added dough enhancers.
If you want to keep the bug going for further brews, halve the solid, add 1 1/2 cups plus 2 1/2 tablespoons (400 ml) water and start again. Keep the bug loosely covered in a warm place.