A study on acetification process to produce olive vinegar from oil mill wastewaters

In this study, two different acetification procedures to produce olive vinegar (OV) from oil mill wastewaters (OMW) were assayed. Specifically, (i) alcoholic-acetous double fermentation with addition of Saccharomyces cerevisiae starter was compared with (ii) spontaneous acetification, without addition of any starter. Within few days from their production, the OMWs were diluted with distilled water (40:60, v/v) and supplemented with sucrose (100 g L−1) and yeast nutrients (0.5 g L−1). Both the procedures gave a satisfactory acidification, leaving a final acetic acid concentration of around 4% on average. Significant amount of residual sugars, especially fructose, was found in the OV by spontaneous acetification. Therefore, in relation to the consumed sugars, spontaneous acetification has been more performing in terms of acetic acid formation; in addition, the acetogenesis appeared to occur bypassing the alcoholic fermentation. Finally, both spontaneous and starter-driven OVs were permanently clear, with a vinous red color and without any abnormal smell.