Put the barley and chopped raisins into an earthenware jar. Do not peel the potatoes but cut them into very small pieces or grate them. Add them to the barley and raisins, with the sugar. Pour on one gallon of hot, but not boiling, water and stir until the sugar has dissolved. Add the yeast and leave for twenty-one days, stirring every day. Strain and bottle, leaving the corks loose for a week or two. Cork firmly and leave at least six months before use.