Of all the senses (sight, sound, smell, touch, and taste) the sense of taste is the one that is described the least in the story. There are, however, some references to food and drink.
For example, describing the morning when Rolf left to go the scene of the volcano eruption, the narrator recalls that she was "sat in the kitchen, sipping (her) coffee." Here the writer evokes the taste of coffee to emphasize how normally the day started. Coffee is a taste which most people associate with warmth, familiarity, and pleasure. By evoking this warm, familiar, and pleasant taste, the writer emphasizes, by contrast, how discomforting, unfamiliar, and unpleasant the day became when Rolf arrived at the scene of the eruption.
The taste of coffee is evoked again later in the story. Somebody brings some coffee to Rolf, who then "help(s) the girl drink it, sip by sip." Describing the effect of the coffee on the girl, the narrator says that the "warm liquid revived her." The writer here perhaps evokes the warm and pleasant taste of coffee to again emphasize, by contrast, the coldness and unpleasantness of the girl's situation.
Later in the story, Rolf feeds the girl with "a cup of the cornmeal mush and bananas the Army was distributing." The taste evoked here is perhaps not particularly pleasant, and also seems like the kind of food one might serve in hospital or to a baby. This then helps to emphasize how helpless the girl is in this moment. The fact that the girl "immediately vomit(s)...up" the food implies how weak she has become. For those of us unfortunate enough to remember what the taste of vomit is like in our mouths, this detail also perhaps helps us to empathize with the girl. She is trapped in the mud, cold and weak, and with the acidic taste of vomit in her mouth.