Lactic acid (LA) production through non-sterilized open fermentation of food waste without inoculum addition was investigated. Results from laboratory-scale experiments indicated that the optimal solid–liquid ratio was 1 : 1 (water content 91.7%). Addition of α-amylase could significantly accelerate the hydrolysis of food waste and consequently increase LA productivity. During the pilot-scale fermentation, the highest LA concentration (21.5 g L−1) was achieved at 48 h. After 48 h, the LA concentration decreased and the byproducts (mainly acetic acid and propionic acid) concentration increased, which was likely caused by the increased cell density of microorganisms other than lactic acid bacteria. After 48 h of fermentation, the total sugar and suspended solids concentration decreased by 65.7% and 61.8%, respectively, suggesting that the LA fermentation was beneficial to achieve the harmless reduction of food waste. The results from this study demonstrated the feasibility of LA production from food waste fermentation without sterilization and extra inoculum addition.
