Used to do this when I was a kid. Yeast,sugar,ground ginger,warm water. Leave it too forment and keep 'feeding' it with sugar and ginger for a week. Has to be kept warm,dark and covered. Then you keep some back for the next batch and add water, lemon juice then seive/filter and bottle.
Does anyone have a recipie for this? I was talking to DCs about this and they want to make this in the holidays.