Simultaneous yeast–bacteria inoculum: a feasible solution for the management of oenological fermentation in red must with low nitrogen content

The simultaneous inoculum of yeasts and bacteria is a feasible solution for improving fermentation in wines with a harsh chemical composition, capable of inhibiting microbial activity. Considering the risk of wine spoilage due to lactic bacteria, co-inoculum is suggested in white wines with a low pH. However, climate change has also caused problems in achieving malolactic fermentation in red wines, due to the high concentration of ethanol and the low nutrient content. In this work, 5 pairs of commercial oenological starters were tested in simultaneous fermentation, using 4 red musts with a low nitrogen content, and compared with a traditional winemaking process. The simultaneous inoculum caused a slowdown in the activity of yeasts, although no problems in the accomplishment of alcoholic fermentations were observed. More reliable malolactic fermentation was performed in the co-inoculum trials, while, in traditional winemaking, some failures in the degradation of malic acid were observed. Microbiological analyses agreed with these observations. No differences were found in yeast density during alcoholic fermentation, demonstrating the absence of negative interaction between the yeast and the bacteria. However, simultaneous fermentation is not without risks; the highest increases of acetic acid were noted in the coinoculum trials. The addition of yeast and bacteria to must with a serious lack of nutrients would appear to be a promising alternative to traditional fermentation; however, careful control of the chemical composition of must is mandatory to obtain reliable microbiological activity in the first stages of winemaking.