The food industry generates a vast amount of food waste. Nevertheless, several types of food waste, i.e. those deriving from fruits, vegetables, grains, and other plant-based food production and processing chains, still contain valuable nutritional and bioactive compounds thus having the potential to be converted into value-added products. Several approaches have been investigated as pre-treatment of food waste to improve the nutritional, functional, and technological properties before to re-inclusion in food production. Sourdough fermentation, either spontaneous or through selected microbial strains, appears to be a suitable and sustainable tool for upcycling plant-derived food waste. This review reveals the latest insights into the potential of sourdough fermentation to recycle milling by-products, brewers' spent grain, wasted bread, and miscellaneous plant wastes. Sourdough biotechnology is suitable for improving the sustainability of several food chains. Nevertheless, due to the significant effect of the presence, growth, and metabolic activity of specific microorganisms on the quality of the final products, an accurate set-up and optimization of tailored fermentation processes is highly suggested. •Sourdough fermentation is a tool to improve nutritional value of food waste.•Microbial starter selection is of main importance for tailored fermentations.•Sourdough fermentation improves the sustainability of several food chains.