Weigh the grapes and allow three fourths pound of sugar to a pound of fruit. Rinse the bunches of grapes in cold water, drain and squeeze the pulp from the skin of each grape. Heat the pulp gradually and cook until the seeds come out easily. Ten or fifteen minutes will be required. Pass through a sieve just fine enough to keep back the seeds. Cook the skins and the pulp ten minutes, then add the sugar and continue cooking until the liquid thickens slightly. Store in earthen or glass jars.