The magadi is added to neutralise the acidity of the bananas and beans and to help them soften into a smooth mash.
Green bananas and beans are boiled together and pounded into a single soft, mildly sour mash, its pale greenish color often coming from a pinch of magadi. It's a Chagga dish traditionally served at funerals, weddings and other gatherings around Kilimanjaro and Arusha.