In a small bowl, dissolve the yeast in 250ml of lukewarm water. Let stand until foamy, about 10 minutes.
In a large bowl, stir together the litre of warm water, salt, ginger, sugar, fennel, treacle and melted butter. Mix in the yeast slurry and rye flour, breaking up any lumps of flour with a whisk. Stir in sultanas. Work in the bread flour 100g at a time, until the dough becomes stiff.
Then, turn it out onto a floured surface and knead in as much of the remaining flour as necessary to make a stiff but workable dough. Knead for an additional 10 minutes to develop the gluten. Place dough into a oiled bowl, and turn to coat. Cover and let rise until double, about 1 hour. Punch down the dough and let it rise again until double.
Remove dough from bowl, and divide into 4 equal pieces. press out air bubbles, and roll dough into loaves. Place the loaves into four well greased 450g loaf tins. Let rise in a warm place until doubled in size.
Preheat the oven to 180 C / Gas 4. Bake the loaves for 40 to 45 minutes, or until the tops are nicely browned, and the loaves sound hollow when tapped on the bottom.