Put the wheat flour in a bowl. Pour the yeast and a teaspoon of Salt into the bowl and add some water. Cover and leave in a warm place for 20 minutes. During this time the yeast may dissolve and start to swell.
Add the whole-grain flour, cumin and vinegar and the rest of the water and knead everything thoroughly. Cover and leave to swell for at least another hour in a warm place.
Preheat the oven to 250 degrees.
Knead the dough again. If it is too moist and sticky, knead in some more flour. Then form a round loaf on a floured work surface. Brush it with some beer, cut the surface and add some flour on top.
Place a small pot of water on the bottom of the oven. That's how a steam can be created in the oven for a crusty top. Put the dough on the middle of the shelf and bake for about 10 minutes at 250 degrees
Then turn down to 220 degrees and bake for about 40 to 50 minutes. The bread is ready when it sounds hollow when you knock on the bottom.