Poi is a Hawaiian preparation of taro root. The starchy taro is cooked, mashed, thinned with water, and then allowed to stand for one to three days. Lactic acid bacteria sour it, and produce some volatile acids as well (vinegary acetic, cheesy propionic). In longer fermentations, yeasts and Geotrichum molds also grow and contribute fruity and mush-roomy notes.
Citron peel, candied from a relative of the lemon, owes its traditionally complex flavor to fermentation. Originally the citron fruits were preserved for some weeks in seawater or a 5 to 10% brine while they were shipped from Asia and the Middle East to Europe; now they’re brined to develop flavor. Yeasts grow on the peel and produce alcohol, which then supports acetic acid bacteria. The result is the production of volatile esters that deepen the aroma of the peel. The preserved lemons of Morocco and other north African countries have a similar character; they’re made by packing cut lemons with salt and fermenting for days to weeks.