Icelandic Thunderbread: Rúgbrauð

An Icelandic rye bread born from steam, patience, and a hint of mischief.

Icelandic Thunderbread

This dense, gently sweet rye bread carries a story as earthy as the landscape it comes from. In Iceland, the dough is traditionally sealed in small pots and lowered into geothermal springs, where it rests for twelve hours or more. By morning, a dark, tender loaf emerges — sliced thin and often served with something smoked, cured, or pickled. I like it best in its simplest form: still warm, with a quiet layer of salted butter.

Its nickname, Thunderbread (þrumari), has a playful origin. Icelanders say it with a smile, hinting at the bread’s remarkable density and fiber — qualities that can stir a bit of internal weather after a hearty slice. A culinary joke, passed down with affection.

Part of the bread’s charm is how straightforward it is to make. No kneading, no rising, no careful tending. Leavened with baking soda and baking powder rather than yeast, it comes together in a single bowl. Mix, let it bake slowly, and time does the rest.

Today, on this rainy Sunday in Friesland, I’m baking it again — a small, warming ritual against the grey weather outside.

Below are two versions of the recipe: one for the oven, and one for a slow cooker.

OVEN RECIPE

What You Need:

• 310g rye flour

• 180g whole wheat flour

• 2 tsp baking soda

• 1½ tsp salt

• 1 tbsp molasses

• 1 tbsp honey

• 400–450 ml buttermilk (start with 400 ml, add up to 50 ml if dry)

• 1 tsp apple cider vinegar (optional for better rise)

What You Do:

1. Preheat oven to 180°C (350°F)

2. Grease loaf pan. Mix dry ingredients in large bowl.

3. Stir molasses, honey, and vinegar into buttermilk. Add to dry and mix.

4. Pour the batter into a greased loaf pan or cake form, then use a wet spoon or spatula to smooth the surface evenly.

5. Bake 60–75 min, or until skewer comes out clean.

6. Cool 10 min in tin, then remove and cool fully.
   

For a vegan version, mix 400 ml oat or soy milk with 1½ tbsp apple cider vinegar or lemon juice. Let sit 10 min to curdle slightly, then use as a buttermilk replacement.

If replacing molasses, especially for flavor and baking soda activation, try: 1 tbsp honey + 1 tsp vinegar or lemon juice
This replaces both the sweetness and acidity of molasses — ideal when using plant milk + baking soda.

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RECIPE FOR SLOW COOKER

What You Need:

• 155g rye flour

• 90g whole wheat flour

• 1 tsp baking powder

• ½ tsp baking soda

• 1 tsp salt

• 1 tbsp molasses

• 2 tbsp brown sugar (optional)

• 200–220 ml buttermilk (or plant milk + 1 tbsp vinegar)

What You Do:

1. Grease a 750 ml heat-safe bowl.

2. Mix dry ingredients in one bowl. In another, combine milk + molasses.

3. Mix wet into dry. Knead lightly into soft dough (not sticky).

4. Shape into ball, place in bowl. Cover with foil and rubber band.

5. Put bowl in slow cooker. Add hot water halfway up sides.

6. Cover slow cooker. Set to HIGH. Steam for 2.5 hours.

7. Remove, cool slightly, then remove from bowl and slice.

Photographing Rúgbrauð on location for the World Wide Bread project, the foundation for our book The First Ingredient.