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Delayed malolactic fermentation: exploring the stylistic and practical impacts

Though almost universally referred to as malolactic fermentation, the process through which tart-tasting malic acid is converted to softer tasting lactic acid and carbon dioxide released is not technically a fermentation. More accurately it is a conversion or transformation. Though likely as old as wine itself, practical understanding of malolactic is a relatively recent breakthrough. As early as 1837 German oenologist Freiherr von Babo described a “second fermentation” which resulted in increased turbidity. Von Babo’s advice to winemakers was to immediately rack their wines and add sulfur to stabilise. Following a string of influential breakthroughs in the late ’80s, in 1939 the French wine scientist Émile Peynaud outlined the importance of malolactic in making great Bordeaux. By 1960, following work by scientists in California, France, and Portugal, isolated strains of lactic acid bacteria were successfully used to carry out malolactic fermentation in the winery. Nowadays winemakers have a range of malo-centric variables at their disposal. Some choose to inoculate with bacterial cultures while others opt for spontaneity, some experiment with particular cultures of bacteria while others negate warming with site-specific blocking of malolactic. And though not often discussed, there are those who consider delayed malolactic fermentation as being amongst the most impactful of these variables. In this piece, I explore this topic in more detail with the help of some of the worlds most-lauded winemakers and writers.

A primer on malolactic fermentation

Acids are a crucial component in both wine and winemaking. They have direct influences on colour, balance, and taste, facilitate the growth and vitality of yeast during fermentation, and provide protection from bacteria. There are three primary acids and a number of secondary acids in wine, amongst the primary acids, is malic acid. Malic acid can be found in almost all fruit and berry plants and is most often associated with unripe apples. It’s name is derived from the Latin ‘malum‘ meaning apple. The concentration of malic acid varies dependent on a number of factors including variety and climate. Concentration of malic acid peaks in berries just before veraison (as high as 20 g/l). As the vine progresses through ripening, malic acid is metabolised through the process of respiration, by harvest the concentration can be as low as 1 to 9 g/l. Additionally, grapes produced in cool regions tend to be high in acidity, much of which is malic acid

Depending on the grape variety and desired style, many winemakers feel that their wine will benefit from a further reduction in malic acid. This reduction is achieved through malolactic fermentation, or more precisely malolactic conversion, and for the sake of ease in this article, malo. During malo, lactic acidosis bacteria convert the stronger, more tart, malic acid into softer, more round, rich, and oftentimes buttery lactic acid. The conversion is undertaken by the family of lactic acid bacteria (LAB), Oenococcus oeni, and various species of Lactobacillus and Pediococcus. Malo is also a decarboxylation, meaning carbon dioxide is liberated during the conversion.


Malo may occur spontaneously alongside the alcoholic fermentation as LAB can be found naturally in both the winery and in cooperages. However, as is often the case with alcoholic fermentation, many winemakers choose to innoculate, either simultaneously with the alcohol fermentation (known as co-inoculation) or following completion of alcohol fermentation. Inoculation can be kicked off with ‘desirable’ bacteria (usually O. oeni) and is generally considered safer, tending to prevent undesirable bacterial strains from producing “off” flavours. At Ruinart, the research team work with yoghurt manufacturers to identify particular strains of bacteria that will complete malo without producing any of the rich, buttery aromas associated usually with diacetyl.

Conversely, there are winemakers who seek to actively prevent malo. This can be the case with fruity and floral white grape varieties such as Riesling and Gewürztraminer and is usually achieved with the addition of sulfur dioxide, filtering, or by adding a malolactic-inhibiting enzyme.

Though not a strict rule, malo tends to create a rounder, fuller mouthfeel. Malo generally enhances the body and flavour persistence of wine, producing wines of greater palate softness. Many winemakers also feel that better integration of fruit and oak character can be achieved if malo takes place in barrel as opposed to in steel. You can read more about oak in winemaking here. As well as whether to innoculate or complete malo in tank or barrel, and though much less discussed, winemakers also have the option to delay malo. Leaving a period of time before completing the alcoholic fermentation, beginning malo, and between the end of malo and bottling. It is this choice that is the focus of this piece.

Christophe Roumier et al.

I do not point to Christophe Roumier as being the first winemaker to delay malo, a number of Burgundian winemakers before him, including Jacques d’Angerville and René Lafon, had particularly cold cellars, and saw no need to rush when it came to malo. Perhaps fuelled by boyish oneupmanship, wanting to prove to his father that he could himself make impactful decisions, Christophe was among the first vigneron to seriously note the qualitative, and in some sense functional, benefits of delayed malolactic fermentation. In the late 1990s, Christophe invested in cooling equipment to ensure delayed malo, noting that cooling served as a ‘brake’ to both fermentation and malo. It was also Christophe who, in 1999, while studying, had become acquainted with Jacques Seysess, and who later inspired Jeremy to push for experimentation with delayed malolactic fermentation at Dujac. Somewhat serendipitously this trial occurred accidentally in 2000 following the same wine being made in two cellars, one colder than the other, meaning an unintentional later malo. Interestingly, prior to Jeremy and Alec joining the domain, it was Christophe, though many years his younger, who Jacques looked to for a second opinion in the winery, regularly inviting him to come and taste from barrel.


Christophe notes that when delayed, malo tends to be a little slower and less roaring than when it takes place during or shortly after alcoholic fermentation. He also cites less loss of colour and aromatics following delayed malo. Though counterintuitive, and surely requiring both a cold cellar and a particularly competent vigneron, Christophe posits that this reduction in the loss of colour could be due to him using less less SO2 when delaying malo. By delaying malo, Christophe also believes that he can extend the ‘journey’ of his wine on its lees in a low pH environment, helping both stability and ageing with a little reduction. He feels that the wines are enriched by the lees and as such offer better depth and dimension with less volatile acidity.

Too often the conversation surrounding malo is too narrow, commonly reduced to the question of whether or not malo takes place at all. In reality, decisions around malo are much more nuanced, complex and intriguing. Of all of these decisions, the impact of delaying malo and allowing for a period of time post alcoholic fermentation and post malo for the wine to rest are particularly pertinent stylistically. I will discuss some of Christophe’s beliefs about delayed malo and more below.

The practicalities of delayed malo

A range of challenges are often associated with delaying malo, most notably that the time between the end of the alcoholic fermentation and the onset of malo can be troublesome, particularly for red wines. Following alcoholic fermentation, free sulfur dioxide levels are extremely low and in some cases zero. This lack of free sulfur leaves the wine somewhat unprotected from microbial growth, Brettanomyces, and the growth of acetic acid bacteria. Sulfur dioxide cannot be added at this stage as it would inhibit the onset of malo. One cannot consider delaying malo without first considering a wider range of parameters, oftentimes the wider winemaking practises of the winemaker in question are required to evolve and their philosophy and timescale adjusted to execute a clean delayed malolactic fermentation.

Jérôme Legras of Legras & Hais (his wine stocked at Sip Champagnes) notes that too often delayed malo is ‘not a real choice’ and instead can be the symptom of ‘the general opinion that no intervention must always be better’. He tells me his experience with what he refers to as ‘laissez-faire wines’ has been somewhat underwhelming. Jérôme insists that only with careful monitoring does this protracted evolution produce favourable characteristics. He is also under the impression that he can recognise easily wines that have undergone a poorly-managed malo. ‘There is a huge difference between wines aged carefully on the lees that give a luminous attack as well as little fat in the palate and heavy butter notes’ he explains.

Though himself not delaying malo, Jérôme shares commonalities with those I’d call serious advocates of delayed malo. Together, both he and they recognize the need for acute management and a wider, more holistic, take on the winemaking process as a whole. This approach is necessary to optimise conditions in the vineyard, the winery, and the wine itself, in order to ensure a healthy delayed malo. What l hope will become evident throughout the remainder of this piece is the extent to which the decision making involved with delaying malo is considered, precise and skillful.


Writer and winemaker, William Kelley, limiting his comments to red wines, tells me that to delay malo ‘requires certain winemaking choices’ including SO2 at crush and SO2 during élevage if a particularly cold cellar cannot be maintained. Though both Roumier and Seysess note delayed malo to help them reduce overall SO2 addition, Kelley notes that ‘unless one is quite technically competent’ the desire to delay malo could be counterproductive. One must also consider fruit pH, a marker varying vintage to vintage. In warm vintages, riper fruit is more likely to have a higher pH, meaning malo will not only progress quicker but be more difficult to retard. Delaying malo in warmer vintage may require shorter press cycles and macerations to avoid extracting too much potassium and increasing pH further, making malo even more difficult to delay. Kelley points out that if you have particularly ripe fruit and don’t add SO2 at cuvaison malo will likely be complete by the time the wine goes to the barrel. As I’ve already alluded to, cellar temperature is a critical variable in delaying the malolactic in absence of the desire to go wild with SO2. In the late ’90s, Christophe Roumier purchased the equipment necessary to cool his cellar whilst Jacques Seysses constructed an entirely new cellar at Dujac. If the cellar is not kept cool until it warms adequately the following spring, malo will be difficult to keep at bay without SO2. It goes without saying that a healthy primary ferment is also crucial.

Much of this article applies solely to still red wines, in the case of whites and sparkling the process is rather different. As Jérôme pointed out to me, still reds tend to have less acidity and therefore less inhibition of bacteria early on. Additionally, the gap between alcoholic fermentation and malo in still wine and red compared to sparkling is usually longer due to higher alcohol inhibiting the development of bacteria. Jérôme also notes that in the case of sparkling base wines ‘it is OK to be less drinkable and with piercing structure when bottled’ as autolysis happens over many years in bottle. So, in the case of still red wines delayed malolactic fermentation may be appropriate; however, for more fragile still whites and sparkling wines where the desire varies, delaying malo is likely inappropriate.

Extending élevage and enrichment

‘To my mind, delayed malo is interesting in so far as it can permit one to extend élevage’ William tells me. More specifically he points toward stabilisation without filtration or intervention and enrichment from the lees as being particularly interesting. Kelley is not alone in this train of thought. Jeremy Seysses of Domaine Dujac notes that by extending the time his wines can spend safely on the lees not only has he been able to produce wines more resistant to oxidation but also wines with more texture and mouthfeel. Both of the aforementioned are for certain results of extended élevage during which the wine spends longer on the lees. At Dujac, lees are not stirred and the wines are racked far less frequently, sometimes not at all once in the barrel. Kelley takes a similar approach, not stirring or racking at all during élevage. At Roumier, Christophe also finds the longer journey of the lees under low pH afforded by delayed malo to be useful, not only in enriching the wine but also in offering a little reduction. So, to delay malo one must maintain a cool cellar temperature, by maintaining a cool cellar temperature one inhibits both VA and Brettanomyces, thus facilitating a more prolonged safe period on the lees, during which the lees enrich the wine, protect from oxidation and contribute toward reduction to some extent.


The lees enrich wine during élevage with mannoproteins, which help with tartrate stability and may mean less need for the wine to undergo cold stabilisation. Mannoproteins are naturally occurring polysaccharides that are found in yeast cell walls. In Saccharomyces cerevisiae, the cell wall is composed mainly of polysaccharides, some of which are mannoproteins. One study has shown that mannoproteins have tartrate stability effects while further similar studies have confirmed that wine aged on lees can become tartrate stable and therefore do not require cold stabilisation.

The reductive nature of the lees also provides some level of protection against oxidation too, as lees themselves are rather potently antioxidative. So while the term ‘reductive winemaking’ may be something of a misnomer, where winemaking is to some extent anaerobic, as is the case with a wine spending an extended period of time on the lees, the finished wine tends to preserve more fresh characteristics, often retaining a somewhat lighter, fruitier style of wine. It may also be true that this extended élevage enhances the aromatic range of wines, though this is anecdotal with limited empirical support, though some does exist which suggests aroma properties differ depending upon malo timing.

One can see how the need to reduce the temperature of the cellar in order to delay, thus providing a safer environment for the wine to age on the lees, would not only protect against oxidation but also offer enhanced mouthfeel and a style of wine which lends itself towards depth and dimension. Some studies have shown mouthfeel benefits from sequential malo but little work has been done delayed malolactic fermentation. These benefits are echoed by Christophe Roumier who firmly believes this reduction benefits his wines.

Saturated hues and stripping colour

Producers opting to delay malo, particularly those in Burgundy working with Pinot Noir, often cite saturated hues and more rapid colour stability. Something William Kelley alluded to during our email exchange. A saturated hue in this context refers to a more vivid and rich red wine while colour stability refers to the stabilisation of the wine’s free anthocyanins. ‘Colour stability happens at a faster rate with a lower pH, so delayed malolactic results in achieving slightly faster colour stability’ Jeremy explains. Seysess also cites darker colour, echoing Kelley’s earlier sentiments. Christopher Roumier also notes improved colour as a benefit to delayed malolactic fermentation.

Gerbaux and Briffox have shown that increased colour stabilisation can be accomplished where the time between completion of alcoholic fermentation and the onset of malo is increased. Temperatures below 10°C will not only inhibit or delay malo but also help stabilise colour and avoid colour loss in lightly pigmented wines like Pinot Noir. Additionally, Burns and Osborne have shown that delaying malo for increasing time periods reduces the loss of polymeric pigment to the point that no difference can be seen between that and control group which did not undergo malolactic fermentation. They propose a relationship between acetaldehyde, pyruvic acid, malo and colour stabilisation.


Acetaldehyde generated during primary fermentation is the driving force to bind tannins and free anthocyanins, thus stabilising colour. Burns and Osborne have demonstrated the role of acetaldehyde and/or pyruvic acid degradation by O. oeni during MLF as being a cause for reduced polymeric pigment formation in red wine. By extending the period of time between alcoholic fermentation and malo this degradation is delayed and stability can be achieved much quicker meaning a reduction in total loss of colour prior to and during the remainder of the winemaking process.

Both Christophe and Jeremy note that by delaying malo they are also able to use less total SO2, William also agreed this was possible where the appropriate winemaking decisions were taken. This reduction in added SO2, combined with faster stability discussed above, may also contribute to enhanced colour stability. Sulfur dioxide, an antioxidant, has the ability to bind to many substances, while in some cases beneficial this can also present a few problems in red wines. SO2 readily binds to anthocyanins, when bound, the anthocyanins are effectively bleached, which results in lighter coloured wines. By maintaining a cool temperature and low pH, winemakers delaying malo are able to add less total SO2, additionally, acetaldehyde is not degraded by LAB and so colour stability can be achieved quicker, meaning a more saturated hue and vivid colour.

As was the case with extending élevage, the broader range of winemaking decisions associated with successfully delaying malo also contributes toward maintaining an environment and dynamic in which a range of further, arguably attractive, benefits can be realised.

Post-malo élevage and bottling date

Albeit short, and to some extent anecdotal, I wanted to include William Kelley’s thoughts on post-malo élevage and bottling date, in the most part because they are thoughts with which I agree. ‘When talking about the duration of élevage I am increasingly persuaded that we should consider élevage to begin malolactic is complete’ William tells me. What William means here is that the time in barrel, more specifically the élevage, should start once malo is complete, not including the time taken completing malo. Kelley proposes that as a taster he finds a wine which has had 9 months élevage post malo plus 9 months of malo will taste more resolved and less primary than a wine which has had only 4 months of true élevage plus 14 months of malo. It is important to remember that in the truest sense élevage is the progression of wine between fermentation and bottling, it is the settling, raising and maturation of said wine. One ought to consider that whilst malo is active, a wine may not truly experience the benefits of élevage in its true sense.

Without further digressing, the key takeaway here ought to be that where producers opt for delayed malolactic fermentation they ought not be ‘wedded to bottling date’. Where producers are wedded to a bottling date but delay malo, the true élevage is much shorter as to condense the winemaking process into a predetermined timeframe which is centred around a predetermined bottling date. Where this is the case wines often make it to bottle somewhat unresolved and rather blocky. ‘Gerard Potel used to bottle 9 months or so after the end of malolactic, and I think there’s a to of sense to that’ William explains. Interesting thoughts to consider when considering delayed malolactic fermentation.

Functional benefits and closing thoughts

In researching this piece and speaking with those who offered their insight and thoughts, what piqued my interest most was the extent to which what may initially appear to be a simple and somewhat absolute decision to delay malo in fact requires complex systems thinking to successfully achieve. Not only this but when one considers the benefits of delaying malo it is not simply the fact that the malo happens later, though Christophe notes later malo to be more gentle, which proves beneficial but more so the conditions which are required to delay malo themselves bringing about a range of functional and stylistic benefits.

The decision to delay malo requires careful temperature management, notably a cold cellar or cooling capabilities. By cooling the wine, winemakers are able to add less sulfur while also staying off the onset of unwanted microbial growth, thus extending the safe time the wine can spend on its lees. This extended time enhances enrichment from the lees, affords a level of reduction, enhances mouthfeel, and protects against oxidation. This period of time spent safely in the barrel also enhances colour stability by delaying the degradation of acetaldehyde and requiring less sulfur meaning early stability and less stripping. Functionally, by cooling the cellar, winemakers will need to rack less often, use less sulfur, suffer less microbial growth, and experience less VA.

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