A process to prepare propionic acid comprises preparing a fermentation broth of water; at least 30 weight percent hydrolyzed corn mash solids, hydrolyzed sugar cane mash solids, or a combination thereof, based on the combined weight of the fermentation broth as a whole; and propionibacteria; without including the typical, frequently very costly supplementation with vitamin and mineral packages. Surprisingly, these mash solids, which must often be disposed of following syrup production, are capable of supplying the nitrogen, micronutrients, vitamins and minerals known to be needed for propionibacteria fermentation, making their sole or significant use as fermentation mediums far more economical and therefore desirable than other fermentation mediums which require supplementation.