Malolactic Fermentation Explained | Malolactic Fermentation Bacteria | Neal Ewing, SommelierQA.com

What is Malolactic Fermentation?

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Malolactic fermentation is a winemaking process by which certain bacteria convert sharp malic (apple) acid, found naturally in wine, to less sour lactic (milk) acid. Since malic acid remaining in red wines can make their tannins taste harsher, this softening is desired for almost all red wines. It also can be encouraged in white wines like Chardonnay, which are not particularly aromatic. One by-product of the process is diacetyl, which has a buttery aroma, often associated with highly regarded Chardonnays.

The yeasts that initially turn grape juice into wine create an atmosphere of carbon dioxide (CO2); and, since malolactic bacteria need oxygen to survive, their “secondary” fermentation usually does not occur until after the grape juice has become wine and the CO2 has dissipated.

In addition, the wine shouldn’t be too cold (kept above 20C/ 68F), and its protective level of Sulfur Dioxide (SO2) can’t be very high. This is no problem for red wines, somewhat protected by their tannins. But white wines are kept cooler to preserve grape aromas and need more help from SO2 to repel oxidizing bacteria.

What is Malolactic Fermentation in Wine Making? | Neal Ewing - SommelierQA.com

How Does Malolactic Fermentation Apply to Traditional Wine Making Techniques?

Malolactic fermentation has happened naturally for centuries, long before winemakers understood the process, so it’s a very traditional winemaking technique. The required bacteria are usually present in the winery, but they can be purchased, just as some winemakers purchase commercial yeasts instead of relying on yeast in the winery’s atmosphere. It’s a very natural way to make a wine taste softer and easier to drink.

WSET addresses this process differently at different Levels. In Level 2 we wait until our Chardonnay week, so we can show its effects by pouring, side by side, bottles with and without “ML.” In Level 3 we teach it during winemaking week, and return to it in several subsequent weeks, such as white Burgundy week, again using illustrative examples. In Level 4, which has six separate units, it’s part of our vinification unit; our unit on light wines (e.g., again, White Burgundy); and even our sparkling wine unit, as some Champagnes go through the process.

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Neal Ewing
Neal Ewing
Certified Wine Educator (Society of Wine Educators); WSET Diploma; Owner at Phillywine
Neal Ewing DipWSET leads Phillywine, a WSET Approved Programme Provider offering WSET Levels 1 through 4, since 1999. He currently instructs or co-instructs all classes in WSET Levels 2 and 3 and selected Level 4 topics. He has prior industry experience working as the wine manager of a retail shop in New Jersey, the wine buyer for a restaurant in Philadelphia, the leader of a weekly wine club featuring guest speakers from the wine industry, and as a wine writer, including two years spent as a stringer for the Wine Spectator. He also was adjunct wine instructor for four years at Walnut Hill College and for nine years at Drexel University. He has a BA from the University of Pennsylvania.
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http://www.phillywine.com

Neal Ewing DipWSET leads Phillywine, a WSET Approved Programme Provider offering WSET Levels 1 through 4, since 1999. He currently instructs or co-instructs all classes in WSET Levels 2 and 3 and selected Level 4 topics. He has prior industry experience working as the wine manager of a retail shop in New Jersey, the wine buyer for a restaurant in Philadelphia, the leader of a weekly wine club featuring guest speakers from the wine industry, and as a wine writer, including two years spent as a stringer for the Wine Spectator. He also was adjunct wine instructor for four years at Walnut Hill College and for nine years at Drexel University. He has a BA from the University of Pennsylvania.


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