The rising agent isn't commercial yeast at all — it's a living 'bug' fermented from potato, flour, water and sugar, kept alive and fed for days before it's strong enough to leaven a loaf.
A potato-based sourdough starter, known as the 'bug,' leavens a dense, slightly tangy wheat loaf baked until deeply crusted. It's traditionally served warm and buttered alongside boil-up or hāngī at Bay of Plenty marae kitchens, and sold at local bakeries and roadside stalls around Rotorua.