Stuck or sluggish malolactic fermentation (MLF) can be problematic in limiting wine conditions, particularly white and sparkling base musts / wines. In these cases, knowledge of yeast-bacteria strain compatibility and the amount of sulfur dioxide (SO₂) a yeast strain produces are important considerations for successful MLF.

Here, the effects of yeast-derived SO₂ production on O. oeni survival was investigated in laboratory- and pilot-scale co-fermentations in Chardonnay. Further to the S. cerevisiae strain affecting O. oeni survival and MLF, we show that SO₂ production by yeast (to approximately 65 mg/L) can be uncoupled from O. oeni survival in early stages of co-fermentation. Bacterial survival with certain SO₂-producing yeast strains was correlated with early, transient formation of a high concentration of acetaldehyde.  Upon co-inoculation, an extremely low concentration range (approximately 1–44 µg/L) of calculated molecular SO₂ is indicated to regulate O. oeni survival. Possible strain-dependent sensitivity of O. oeni to bound SO₂ may also occur, although the extent and nature of such inhibition by the SO₂ adduct itself during co-fermentation remains unclear.

Choice of co-inoculation yeast strain also influenced wine diacetyl concentration, which was only detected in wines co-inoculated with high-SO₂-producing S. cerevisiae strains. These wines also had comparatively high citation frequency for a buttery sensory attribute. Both the SO₂ and acetaldehyde production capacity of yeasts are therefore seen as meaningful co-inoculation selection criteria. The range of yeast strains suitable for MLF induction by co-inoculation could be widened to include SO₂-producing strains which transiently produce an early, high concentration of acetaldehyde. Reliance on total / bound SO₂ concentration may also potentially provide an inaccurate measure of SO₂ toxicity towards O. oeni, particularly for co-inoculation, and the impact of low, equilibrium concentrations of molecular SO₂ should also be considered.