Beyond that, studies have also shown that malolactic fermentation intensifies fruity, red berry aromas in red wines, especially in wines with lower pH. This can be a benefit, as lower pH wines can have more muted fruit aromas compared to riper, higher pH wines.
When the bacteria do remain active, they produce acetoin and 2,3-butanediol, which contribute much more subtle buttery, creamy aromas as well as others, like nuts and berries. Rorick also points out that the residual yeasts in the lees will also assist in breaking down diacetyl, meaning that the longer the wines spend on their lees after both fermentations, the more they will lose the primary, buttery character that people associate with malolactic fermentation. Davis indicating that by 20 days post-malo, diacetyl levels typically fall below human sensory threshold assuming no SO2 addition and yeast lees contact.
In spite of the strong association between malolactic fermentation and barrel-aged wine, the fermentation vessel is actually quite irrelevant to the process—it can occur in steel tanks or barrels. Some winemakers are using year-old barrels, disproving the premise that they must be discarded after five years.
As grapes ripen in the vineyard, the amount of malic acid can drop significantly, decreasing the probability of spontaneous malolactic fermentation — quite simply because there is little or nothing to convert.
But what might not be as well known is how another process can also block it: carbonic maceration. Malic dehydrogenase , an enzyme, is the compound responsible for this. Similarly, low diacetyl concentrations can represent an "Old World" style, but may not appeal to certain sectors of the market. As diacetyl is largely a byproduct of malolactic fermentation, there are several factors that can be easily manipulated by the winemaker during MLF to achieve their desired diacetyl level including:.
Strains of malolactic bacteria vary in their potential for production of diacetyl. Refer to the figure below to compare strains sold by Scott Labs.
As the diacetyl is being produced, yeast and bacteria will break it down. Similarly, inoculating for MLF following the completion of alcoholic fermentation will contribute to higher diacetyl levels in wine. The shorter the contact time with yeast and bacteria, the higher the diacetyl. This is because living yeast and bacteria break down diacetyl irreversibly. Diacetyl is the same exact molecule used in microwave popcorn, margarines and other "buttery" foods.
It turns out that while these bacteria produce good amounts of diacetyl, they also naturally consume it. So the buttery aroma will be most potent when the wine is at the height of malolactic fermentation and the bacteria are producing more diacetyl than they are consuming. But in the later phases of fermentation, the bacteria are able to convert nearly all the diacetyl, leaving the wine completely void of buttery aromas. Removing the buttery aroma is as simple as waiting a few extra weeks and allowing the bacteria to naturally convert the diacetyl before disrupting the fermentation.
Conversely, a winemaker who wants this element in their wines can stop the fermentation when the aroma is at its peak. While these buttery — and often sweet — Chardonnays had their time in the spotlight more than a decade ago, most premium winemakers now myself included are pushing for the vineyard site and fruit to be front and center. When a white wine of relatively low acidity - like most California and Australian Chardonnay - is put through "malo," you get the familiar butter flavor.
Because this flavor is popular, many wine makers put Chardonnay through "malo" specifically to achieve it. They may turn up the volume even more by holding the wine in oak barrels, which adds spicy, sweet and vanilla aromas and flavors.
So, the presence or absence of "butter" divides the world of Chardonnay into two broad categories that are roughly associated with the wine's geographical origin.
The "Old World" style, characteristic of White Burgundies, produces a wine that's usually high in acidity and bone-dry, focused on fruit, with little or no oak flavor. The "New World" style almost seems like a completely different wine.
Ripe in flavor and often slightly sweet, it's a big Chardonnay with vanilla and tropical-fruit character and a marked buttery aroma and texture.
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