What happens in MLF
Lactic acid bacteria, usually Oenococcus oeni, convert sharper L-malic acid into softer lactic acid, releasing CO₂. TA falls and pH typically rises a little. Grape juice can carry anywhere from under 1 g/L to over 5 g/L malic, so the starting point varies a lot with site and season.
When is it finished?
| L-malic (g/L) | Status |
|---|---|
| Above 0.3 | Underway or stalled — keep monitoring |
| 0.1–0.3 | Nearly there; some treat below 0.2 as complete |
| Below 0.1 | Generally accepted as complete |
Test every one to two weeks while MLF is active. If malic stops dropping for two consecutive tests, check temperature, SO₂, pH and alcohol — the usual reasons bacteria stall.
After MLF
Sulphur promptly once malic confirms MLF is complete. The window between MLF finishing and SO₂ going in is when Pediococcus, Lactobacillus and Brettanomyces find an unprotected wine. Then check free SO₂ and pH to confirm you have reached your molecular target.
Wines without MLF
For crisp whites and many sparkling bases, MLF is avoided. Keep SO₂ up after primary fermentation, keep the wine cool, and remove bacteria by filtration before bottling. A malic result before bottling confirms nothing has started on its own.
Plan your MLF checks across the season.
Sampling plannerFermLabs guide · general information only — your own wine's analysis and trials come first.