When lukewarm, mix the yeast with the warm water, pressing out lumps, and add to container. Cover and let stand for 6 hours. Stir the sugar into the ginger beer until completely dissolved and immediately pour into sterilized bottles, making sure the stoppers are well sealed and airtight. The ginger beer will keep for 3 to 4 days in a cool place. To keep longer, add rum.
This recipe yields 4 quarts.