Sift together the rye flour, cornmeal, wheat flour, baking soda, ginger, and salt. Stir in the molasses and buttermilk or yogurt and blend well. Stir in the raisins.

Butter two 1-pound coffee or juice cans, or several smaller cans, generously. Fill each can three-quarters full of batter. Butter pieces of foil and cover the cans, sealing well with tape if necessary.

Place the cans in a large pot and pour in water to a depth of 2 inches. Bring the water to a boil, cover, and reduce heat to very low. Simmer for 3 hours, checking once in a while to make sure the water hasn't boiled off.

Remove the cans from the pot, unmold, and cool on a rack. If your bread seems too moist, place in a moderate oven for 10 minutes.