Maas

maas an African beverage, favoured by the Zulus and sometimes called amass or amasi, resembles a pourable yoghurt.

Emerson gives a pleasing quotation from the book Zululand by the Revd Lewis Grout:

Their amasi, or thick milk, is made by pouring sweet milk into the igula, a large bottle-shaped calabash, where it soon undergoes a kind of fermentation, or acidulous chemical change, from being leavened, as it were, by a little which was left for the purpose when the previous mess was poured out. The whey which is generated by the process is first drawn off and used as a drink, or as food for the little folks; then comes a rich white inspissated substance, which is neither curd nor bonny-clabber, nor buttermilk, nor anything else but just that light, acidulated, healthy, and to most persons very acceptable, dish which the natives call amasi.