Place about 850 g flour, salt, yeast, and baking soda in the bowl of a stand mixer. Add the whey, ginger syrup, and butter. Mix until a smooth, shaggy dough comes together.
Add additional flour, about 75 g or so at a time, until the dough comes together and pulls away from the sides of the bowl. Knead in the mixer about 5-7 minutes, until dough becomes smooth and elastic. Or turn out onto a lightly floured surface and knead by hand about 10-15 minutes.
Place dough in an oiled bowl, turning once to cover, and allow to rise in a warm place for about 60 minutes, or until doubled in size.
Preheat oven to 350 F.
Divide dough into three equal portions and shape into loaves. Place each loaf into a greased, 9"x5" loaf pan. Spray the tops lightly with cooking spray, cover with a clean towel and allow to rise for about 45 minutes, or until the top of the dough is about an inch above the sides
Bake for 35-40 minutes, or until tops are deep golden and an internal temperature of 190 F has been reached. Turn loaves out onto a cooling rack, and coat tops with butter.