This article explores practices and findings to modulate diacetyl in wine through the choice of the right selected wine bacteria and inoculation strategies.
Diacetyl management in winemaking is a key tool to shape the aromatic profile of wines.
During malolactic fermentation (MLF), selected wine bacteria not only soften acidity and improve mouthfeel, but also influence fruity, floral, or spicy notes.
Among these effects, the production of diacetyl by certain selected wine bacteria plays a central role, adding buttery or creamy aromas highly valued in certain wine styles, especially Chardonnay.
What is the effect of diacetyl in wine?
- At low concentrations, diacetyl adds yeasty, nutty, and toasty aromas.
- At medium levels (1–4 mg/L), depending on the wine type, it contributes desirable buttery/butterscotch notes.
- At high levels (>5–7 mg/L), diacetyl is considered undesirable by consumers.
- The sensory threshold varies by varietal:
- 0.2 mg/L in Chardonnay
- 0.9 mg/L in Pinot Noir
- 2.8 mg/L in Cabernet Sauvignon
What are the key factors influencing diacetyl formation?
- Oxygen levels – semi-aerobic conditions increase diacetyl up to sixfold compared to anaerobic.
- Citric acid metabolism – wine bacteria strain-dependent, with later metabolism linked to lower diacetyl.
- Temperature – lower MLF temperature tend to slow down the MLF rate (18 °C vs. 25 °C) and lead to higher diacetyl concentration.
- SO₂ – binds diacetyl reversibly; as SO₂ decreases during aging, free diacetyl rise, and so its sensory impact.
- Choosing the right selected wine bacteria to produce fruit-driven wines or buttery wines.
What is the role of selected wine bacteria in producing diacetyl during MLF?
- In sequential inoculation: Certain selected wine bacteria such as UVAFERM BETA™ or PN4™ can produce high diacetyl. This is linked to the timing of citric acid attack: the earlier it occurs (beginning to mid MLF), the higher the diacetyl production.
- Citrate-negative selected wine bacteria: Being ‘citrate-negative’ does not reliably prevent diacetyl production in wine bacteria. Diacetyl can still form via other pathways, and strain-specific behaviour plays a more important role than citrate metabolism.
Co-inoculation vs. sequential inoculation?
- Co-inoculation (selected wine bacteria addition within 24h after selected wine yeast inoculation):
- Produces fruit-driven wine styles as opposed to the lactic, buttery or nutty styles that may result from sequential inoculation.
- Leads to negligible diacetyl formation, as wine yeast reduces diacetyl into acetoin and 2,3-butanediol with little sensory impact.
- Offers earlier wine stabilisation.
- choice of selected wine bacteria has no impact on diacetyl content
- Sequential inoculation (post-AF):
- Can result in significant diacetyl, depending on the selected wine bacteria strain.
- Useful for creating wines with buttery or creamy complexity.
- Choice of selected wine bacteria is a key factor influencing the concentration of diacetyl.
Our guidelines to shape the diacetyl profile of wines
For buttery-style wines (high diacetyl production):
- Use sequential inoculation with high-producing selected wine bacteria strains (e.g. PN4™).
- Short lees contact.
- Long MLF – low pH and/or low temperature
- Oxidative conditions.
- Quick SO₂ stabilisation after MLF.
For fruit-driven wines (low to no diacetyl production):
- Use LALVIN VP41™, O-MEGA™, UVAFERM BETA™ in co-inoculation
- Use low-producing selected wine bacteria in sequential inoculation (e.g., LALVIN VP41™, O-MEGA™).
- Long lees contact.
- Shorter MLF with warmer fermentation conditions.
- Reductive conditions (no stirring during MLF).
- Delayed SO₂ addition, once the desired diacetyl level is reached.
Conclusion
Diacetyl in winemaking is a stylistic lever for both white and red wines. The timing of inoculation and the choice of selected wine bacteria are the most important factors influencing buttery vs. fruit-driven profiles.
Learn more about how Lallemand Oenology selected wine bacteria and yeasts can help you shape wine style through diacetyl management by reading our dedicated Winemaking Update here below.
Manage diacetyl in your wines
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Published Sep 26, 2025 | Updated Oct 15, 2025
Wine Bacteria