Wearing heavy rubber boots, Fränz Röösli climbs atop his charcoal pile and starts poking holes into what he calls the “Grind” – the “head” or dome of the pile, which reaches four meters above ground. White smoke rises from the holes, curling around the charcoal burner to the whims of the wind before it is carried off into the dark of night. In calm, stunning images, the documentary “Köhlernächte” by Robert Müller draws the viewer into the archaic world of commercial charcoal burning in Switzerland’s Napf region.