Icelandic Thunder Bread

Icelandic Thunder Bread
Sally Williams Photography/Photo Library/Getty Images
Prep: 20 mins
Cook: 4 hrs
Total: 4 hrs 20 mins
Servings: 12 servings
Nutrition Facts (per serving)
176 Calories
1g Fat
38g Carbs
5g Protein
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Nutrition Facts
Servings: 12
Amount per serving
Calories 176
% Daily Value*
Total Fat 1g 1%
Saturated Fat 0g 2%
Cholesterol 2mg 1%
Sodium 225mg 10%
Total Carbohydrate 38g 14%
Dietary Fiber 3g 10%
Total Sugars 10g
Protein 5g
Vitamin C 0mg 0%
Calcium 111mg 9%
Iron 2mg 9%
Potassium 161mg 3%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
(Nutrition information is calculated using an ingredient database and should be considered an estimate.)

This moist, Icelandic dark rye bread (rugbrauð), also called "thunder bread" or "pot bread," has many similarities to Boston brown bread—it is leavened with baking powder, not yeast, and molasses gives it color and a hint of sweetness. Traditionally, Icelandic rye bread is prepared over the course of 12 or more hours by placing the dough into covered pots and sinking these into geothermal springs. Since most of us do not have a geothermal spring nearby, this recipe cooks the bread in tin cans or ramekins tented with aluminum foil in a slow cooker filled with water. Steaming the bread is the key.

Sources say the name "thunder bread" comes from the after-effects of eating too much of this high-fiber rye. Also, it is served at Thorrablot, the Viking festival in honor of Thor, the god of thunder.


  • 2 1/2 cups rye flour

  • 1 1/2 cups all-purpose flour

  • 1 heaping tablespoon baking powder

  • 1/2 teaspoon salt

  • 1/2 cup packed brown sugar 

  • 1 tablespoon molasses

  • 1 cup scalded milk, cooled to lukewarm

  • 2 cups hot water

Steps to Make It

  1. Gather the ingredients.

  2. Whisk together the rye flour, all-purpose flour, baking powder, and salt in a large bowl or the bowl of a stand mixer.

  3. Mix in the brown sugar.

  4. Stir the molasses into the scalded lukewarm milk until it dissolves.

  5. Then slowly stir the milk into the dry ingredients (the dough hook of a mixer works well).

  6. Knead the dough until it is shiny and all the flour is incorporated. Divide into 2 portions.

  7. Butter the insides of 2 tin cans (at least 19 ounces each—watch out for sharp edges) or 2 ceramic bowls or ramekins, each one large enough to hold 1 1/2 cups of batter.

  8. Pour the bread dough into the cans, bowls, or ramekins.

  9. Tent the molds with aluminum foil, leaving about an inch of headspace for the bread to rise as it cooks. Secure the edges of the foil tightly around the rims of the molds with twine or rubber bands.

  10. Place the molds in your slow cooker. (If using cans, place on a trivet or canning jar lid inside the cooker to help the steam circulate.) Pour enough hot water into the slow cooker to cover the lower half of the molds (about 2 cups).

  11. Put the lid on the cooker and raise the heat to high. Allow the water to simmer for 4 hours, checking occasionally to ensure that the water hasn't boiled out. Add more water if necessary.

  12. Remove the molds, turn out the bread, and serve immediately.

  13. Enjoy with butter, cold pickled herring, lamb pâté, cold meats, or cheese.


  • The dough will rise while cooking, so whichever molds you use, make sure to fill only two-thirds full with the bread dough.
  • It is important to check the water level every so often in the slow cooker, so you can't leave it unattended for hours. If the water level is low, you need to add more water to keep the bread steaming.
  • You can make the bread vegan by substituting soy milk for the regular milk.