Malo-lactic fermentation (MLF) is the bacterial conversion of malic acid to lactic acid. Wines which have undergone MLF are typically softer (less acidic). MLF with commercial cultures is desirable in reds and some white wines to enhance stability. Many wineries encourage MLF to prevent spontaneous fermentation by less desirable bacterial strains. It should be noted that MLF is inhibited where free SO2 levels exceed about 30 ppm. Ideal conditions for MLF are lower alcohol levels, pH above 3.3, free SO2 of less than 30 ppm and a temperature above 20 degrees Celsius.