Malolactic Fermentation vs No Malolactic
Round and creamy versus crisp and bright: how one bacterial conversion of malic acid into lactic acid reshapes a wine's acidity, texture and stability.
Malolactic fermentation (MLF) is the conversion of malic acid into lactic acid by lactic acid bacteria, most commonly Oenococcus oeni, and Decanter notes it is technically a bacterial conversion rather than a fermentation because it does not use yeast. The Australian Wine Research Institute (AWRI) describes its role as three-fold: reducing wine acidity, stabilising the wine by removing L-malic acid, and shaping aroma and flavour. Wine Spectator calls it a standard practice "used in pretty much all red wines and many whites", while Decanter names aromatic, high-acid whites such as Riesling and Sauvignon Blanc as styles where it is generally undesirable. WSET frames the choice as one that often comes down to house style: MLF creates a rounder, creamier wine, and producers who want fresh wines block it to retain bright acidity.
Wine Spectator describes MLF as the conversion of malic acid to lactic acid and carbon dioxide by lactic acid bacteria, primarily Oenococcus oeni. AWRI attributes O. oeni's leading role to its ability to survive the harsh conditions of wine: high alcohol, low pH and low nutrients. MLF can start from the natural bacterial flora or from an inoculated strain, and AWRI lists inoculation timings from co-inoculation with the yeast, through mid-fermentation and pressing, to the most common option, after alcoholic fermentation (sequential inoculation).
Without MLF the wine keeps its malic acid, which Wine Spectator associates with tart green apple flavors. Wine Spectator lists three main ways to prevent MLF: adding sulfur dioxide to kill the bacteria, filtering the wine to remove them, or adding a malolactic-inhibiting enzyme before bottling. Decanter names SO2 added post-fermentation and enzymes such as lysozyme as the tools winemakers use to inhibit it. AWRI's conditions table for white and sparkling base wines rates pH below 3.1, temperatures below 12°C and total SO2 above 60 mg/L as harsh for malolactic bacteria, and gives 0.3 to 0.5 mg/L molecular SO2 as a lethal concentration for wine bacteria.
AWRI lists buttery, vanilla-like, nutty, spicy, fruity, vegetative, toasty, fuller and rounded as sensory terms used to describe MLF influences on wine. Diacetyl, which O. oeni forms from citric acid during MLF, gives a buttery or butterscotch aroma; Oregon State University Extension notes it can be objectionable at high concentrations (above 5 mg/L) but may be desirable at lower levels, depending on the wine style. The official Champagne website says MLF introduces notes of brioche and butter. In red wines, AWRI links MLF with red berry and dark berry descriptors, and Decanter says MLF in barrel can promote a wine's smoky and spicy notes.
Skipping MLF keeps the malic acid that Wine Spectator ties to tart green apple flavors. WSET links notes of lemon, lime, grapefruit or green apple in a white wine to a strong acidic backbone. Wine Spectator frames the decision for white wines as a choice between a crisp, bright white (skip the malo) and a fuller-bodied, rich white (full malo).
WSET says converting sharper malic acid into softer lactic acid "creates a rounder, creamier wine", and Wine Spectator notes that in white wines ML tends to soften acidity and can impart a creamy mouthfeel. AWRI explains the chemistry: malic acid can give two protons in wine and lactic acid only one, so pH should rise after MLF, and titratable acidity (expressed as tartaric acid) drops by 0.56 g/L for each g/L of malic acid converted, so a wine starting with 2 g/L of malic acid would be expected to drop by 1.12 g/L. Oregon State University Extension adds that for cool-climate wines with high levels of malic acid, this decrease in acidity is essential to wine balance.
WSET says producers who want fresh wines block MLF "to retain that bright acidity". It describes higher acidity as making the mouth water quickly with an effect that lingers, while a wine with little salivation that feels soft and rounded is likely low in acidity.
Wine Spectator calls ML standard practice in pretty much all red wines, and AWRI reports that in Australia almost all red wines undergo MLF and 74% are inoculated with bacterial starter cultures (Nordestgaard 2019). Among whites, Decanter names Chardonnay and Viognier as grapes that routinely go through malo. In Champagne, the official Champagne website says MLF is optional and up to each winegrower, who may carry it out fully or only partially, or avoid it altogether. Decanter reported that in the 2014 Bordeaux vintage several white wine producers took the unusual step of putting Semillon or Sauvignon Blanc through MLF to tame high acidity.
Decanter names aromatic, zingy, high-acid whites such as Riesling and Sauvignon Blanc as styles where MLF is generally undesirable. It adds that reds grown in very warm climates that lack natural acidity do not benefit from the process, because it makes them less balanced and unstable. WSET sets cool-climate Chablis, with pronounced acidity and bright citrus flavours, against a warm-climate, oak-aged Chardonnay shaped by MLF and time in barrel to show how the same grape can taste completely different.
AWRI calls MLF crucial to microbiologically stabilise most red wines: it removes the malic acid that can be a carbon source for yeast and bacterial growth, leading to spoilage, spritz and unwanted flavours. AWRI recommends aiming for a malic acid result of 'not detected', usually below 0.05 g/L by enzymatic analysis, and treats 0.1 g/L or less as low enough for MLF to be considered virtually complete. Wine Spectator adds that intentionally initiating ML ensures it will not take place later, accidentally, in the bottle.
A wine that skips MLF keeps its malic acid, and Wine Spectator warns that an accidental ML in the bottle "can turn a wine into a cloudy, smelly, fizzy mess". Decanter likewise notes that the bacteria are often present in the cellar, so spontaneous MLF can occur, and that doing MLF helps prevent it happening later, potentially after bottling. Blocking therefore depends on the controls Wine Spectator lists: sulfur dioxide, filtration, or a malolactic-inhibiting enzyme before bottling.
MLF raises pH (AWRI, Decanter), and AWRI notes that higher pH favours malolactic bacteria but also potential spoilage organisms, including certain strains of Pediococcus and Lactobacillus; for red musts and wines expected above pH 3.5 it suggests co-inoculation and prompt stabilisation after MLF. Oregon State University Extension reports that color loss due to MLF, driven mainly by lower concentrations of polymeric pigments, occurs whether MLF is simultaneous or sequential.
WSET says acids act as natural preservatives that allow fine wines to age for a decade or more, and that acidity lets a red matured for decades retain its freshness long after the fruit has softened. WSET names climate as the single biggest influence on a wine's acidity: wines from cooler regions hold onto more of their tartaric and malic acid, while warmer regions and vintages tend toward lower acidity.
WSET says the choice often comes down to house style. AWRI lists bacterial strain and inoculation timing among the levers for shaping MLF character: co-inoculated MLF would be expected to give lower buttery character because yeast can metabolise diacetyl to acetoin and 2,3-butanediol, and Oregon State University Extension advises a sequential MLF with a high diacetyl-producing strain for a wine meant to show buttery aromas. Decanter notes that wines typically aged in oak undergo MLF, and names a creamy, oily texture, a rounder acid profile and a higher pH as clues that a wine has gone through malo.
Blocking MLF is the choice WSET ties to producers who want fresh wines with bright acidity, and Wine Spectator to a crisp, bright white. It takes active control in the cellar, using SO2 after fermentation, filtration, or an enzyme such as lysozyme (Decanter, Wine Spectator). Champagne shows the choice need not be all or nothing: the official Champagne website says growers may carry out MLF fully, only partially, or avoid it.
Reach for a wine that went through MLF when you want a rounder, creamier texture and softer acidity, the profile WSET describes in oak-aged Chardonnay and the norm Wine Spectator describes for pretty much all red wines. Reach for a wine made without it when you want bright, retained acidity, the fresh style WSET ties to blocked MLF and the high-acid aromatic whites, such as Riesling and Sauvignon Blanc, where Decanter calls MLF generally undesirable. WSET notes the decision often comes down to house style, and in Champagne growers may also choose a middle path of partial MLF.
- MLF is the conversion of malic acid into lactic acid by lactic acid bacteria, mainly Oenococcus oeni; Decanter and Wine Spectator both note it is technically a conversion rather than a fermentation.
- AWRI gives MLF three roles: reducing wine acidity, stabilising the wine by removing L-malic acid as a potential energy source, and shaping aroma and flavour.
- Chemistry: malic acid can give two protons in wine and lactic acid one, so pH rises after MLF and titratable acidity (as tartaric acid) falls by 0.56 g/L for each g/L of malic acid converted (AWRI).
- Diacetyl, formed from citric acid by O. oeni, gives the buttery note; Oregon State University Extension flags concentrations above 5 mg/L as potentially objectionable, and co-inoculation tends to lower it.
- Styles: Wine Spectator calls ML standard in pretty much all reds and many whites; Decanter names Chardonnay and Viognier as whites that routinely go through malo and Riesling and Sauvignon Blanc as styles where it is generally undesirable; blocking uses SO2, filtration or an enzyme such as lysozyme.
Sources and last verified
Sources: https://www.awri.com.au/files/attachment/mlf-in-red-wine/, https://www.awri.com.au/files/attachment/mlf-in-white-and-sparkling-wine/, https://www.awri.com.au/wp-content/uploads/mlf_modulation_AWRI_fact_sheet.pdf, https://www.awri.com.au/files/attachment/malolactic-fermentation-2/, https://extension.oregonstate.edu/catalog/em-9641-simultaneous-malolactic-fermentation-it-right-option-your-wine, https://www.champagne.fr/en/from-vine-to-wine/wine-making/malolactic-fermentation-clarification, https://www.wsetglobal.com/knowledge-centre/blog/2026/understanding-acidity-in-wine, https://www.decanter.com/learn/what-is-malolactic-fermentation-51591/, https://www.winespectator.com/articles/what-is-malolactic-fermentation-and-why-do-winemakers-use-it, https://www.winespectator.com/articles/how-do-you-prevent-a-wine-from-going-through-malolactic-fermentation-44557. Last verified 2026-09-28.
