Stir together yeast, 1/2 cup flour and warm water in a large bowl. Cover and let sit in a warm spot for about 30 minutes. Stir beer, remaining flour and salt into the bowl. Mix until all the flour is incorporated and forms a thin sticky dough that pulls away from the sides of the bowl. Cover and let rise in a warm spot for 2 hours, until doubled in size.
Scrape all the dough from the bowl with a rubber spatula then place on a well-floured surface. Generously flour the top of the dough and form into a loaf shape. Line a baking tray with baking paper. Transfer loaf to the baking sheet and sprinkle the top with flour. Cover loosely with a towel and let rise for 30-40 minutes.
Preheat the oven to 220 degrees C. Place a small pan of warm water on a lower rack to humidify the oven.
Slash a long slit in the top of the loaf with a sharp knife. Place the baking tray on the rack above the pan of warm water in the oven. Bake for 35 minutes, until the loaf is golden brown. Transfer to a cooling rack. Let cook completely before slicing and serving.