WinemakerOS

Why Malic Acid Matters

Grapes arrive with two primary acids: tartaric and malic. Tartaric is stable — it stays in your wine unless you cold-stabilize it out. Malic is different. It's sharper, greener, and biologically active. Given the right conditions, bacteria will convert it to lactic acid through malolactic fermentation (MLF).

That conversion softens the wine's acidity, adds texture, and introduces buttery or creamy notes depending on the strain and conditions. For full-bodied reds and barrel-fermented Chardonnay, that's usually a feature. For Riesling, Sauvignon Blanc, or a fresh rosé, it's a flaw you have to prevent.

The problem is that MLF doesn't always happen when you want it to — and it doesn't always stop when you want it to either. Managing malic acid means actively steering the process, not hoping for the best.

Testing for Malic Acid

The simplest field method is paper chromatography. It's inexpensive, runs overnight, and gives you a clear visual read on whether malic acid is present, declining, or gone. Most small wineries run chromatography every one to two weeks during MLF to track progress.

For a more precise number, enzymatic assay kits (available from Vinquiry, ETS, and others) give you malic acid concentration in g/L. This is useful when you need to know if MLF is “complete enough” for a style decision, not just whether it's happened at all. Aim for below 0.3 g/L before calling MLF complete in wines you want fully converted.

Paper chromatography is fine for most small-winery workflows. Enzymatic testing pays off when you're managing a large program or working with wines that have tricky pH and SO₂ interactions.

When to Encourage MLF

Most red wines benefit from MLF. Malic acid in a Cabernet or Syrah reads as harsh and vegetal — lactic acid from MLF integrates better with tannin and oak. The practical trigger: inoculate with a commercial ML culture (Oenococcus oeni is standard) after primary fermentation is complete and the wine is around 10–15 mg/L free SO₂. Higher SO₂ kills the bacteria before they can establish.

Temperature matters too. Keep your cellar above 60°F (15°C) during MLF — ideally 65–72°F. Below 60°F, ML bacteria stall. Some small wineries inadvertently block MLF by moving reds to a cold storage area too early and then wonder why the wine tastes sharp six months later.

Co-inoculation — adding ML bacteria at the same time as yeast — is gaining traction in small-winery practice. It shortens the overall process, reduces risk of spoilage organisms establishing during the waiting period after primary fermentation, and can work well with compatible yeast/bacteria pairings. Check manufacturer recommendations before trying co-inoculation with every strain.

When to Block MLF

Crisp whites and most rosés benefit from retaining malic acid. It keeps the wine fresh, reduces the risk of a flabby mid-palate, and preserves varietal character. For these wines, your job is to prevent MLF from starting — or stop it if it begins.

The primary tools are SO₂ and cold temperature. After pressing:

Add SO₂ at crush to suppress wild bacteria early.
Ferment and store below 55°F when possible.
Maintain free SO₂ at 25–35 mg/L post-primary fermentation (adjust for your pH).
Use lysozyme if you want a non-SO₂ tool — it's an enzyme that disrupts gram-positive bacterial cell walls, including Oenococcus oeni, without affecting yeast.

If MLF starts anyway — which happens with wild-yeast fermentations or naturally low SO₂ programs — your options narrow quickly. Sterile filtration (0.45 micron) can remove ML bacteria but risks stripping texture. Adding SO₂ late in an active MLF rarely stops it cleanly. Prevention is far easier than intervention.

Tracking It Across Lots

MLF status is one of those things that creates chaos when it's tracked in a notebook or a shared Google Sheet. You end up with two wines in the same tank room at different MLF stages, a note about one of them that nobody updated, and a bottling date that sneaks up before completion is confirmed.

The fix is lot-level tracking tied to dates. Each lot needs a record of when MLF was inoculated, when chromatography or enzymatic tests ran, what the results were, and what action was taken. That record should be searchable when you're standing in the cellar, not buried in a spreadsheet on your office computer.

WinemakerOS builds this into the lot workflow — you log MLF status directly against the lot, set a follow-up reminder to retest, and the system flags any lot that's been sitting in “MLF in progress” for longer than your defined window. It's a small thing that prevents a lot of expensive surprises at bottling.

The Bottom Line

Malic acid management is a decision you make at crush and defend all the way through to the bottle. Decide early whether you want MLF to happen, create the conditions for it (or against it), and test consistently enough to know where you stand. The winemakers who get in trouble are usually the ones checking once and assuming the situation held.