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Malolactic Fermentation: Hero Or Zero?

by Sam Schmitt, Csw

Malolactic fermentation is an often misunderstood technique in a winemaking. Most popularly associated with rich, buttery, and frequently over-oaked Chardonnay, many wine drinkers have inappropriately concluded that malolactic fermentation is a cheap wine making trick used by California Chardonnay producers to artificially fatten-up their wines. The truth, however, is that malolactic fermentation is an important wine making technique that is critical to both the flavor profile and body of a wine.Malolactic fermentation is a bit of a misnomer because it isn’t really a true fermentation process at all. True fermentation is the conversion of sugar into alcohol, carbon dioxide, and heat. In wine making this is usually achieved through yeast metabolism. Malolactic fermentation (ML) is the term used to describe the conversion of malic acid into lactic acid through the metabolism of a family of bacteria called lactic acid bacteria (LAB). Malic acid naturally develops in grapes and is usually associated with the tart flavor of green apples. Lactic acid, on the other-hand, does not naturally develop in grapes and is usually associated with the flavors of butter or cream. In some wines, such as Sauvignon Blanc, Riesling or Pinot Gris, the bright green apple flavor of malic acid provides sharpness and makes the wine seem light and refreshing. In these types of wines, ML is undesirable. However, in many other wines, including almost all reds and some whites that will be aged in oak, a strong green apple flavor is undesirable. ML allows the wine maker to turn down the sharp green apple character of malic acid and replace it with the smoother, richer character of lactic acid. Try to imagine a Cabernet Sauvignon that has a strong green apple flavor; it doesn’t seem that appealing does it?ML isn’t a trick, it is a naturally occurring process. Winemakers often allow ML to begin after primary fermentation has finished and the wine has been transferred to oak barrels which is why it is often referred to as secondary fermentation. Some wine makers may inoculate the wine with a specific type of LAB to generate a specific flavor profile or to prevent possible undesirable strains of LAB from dominating the process. Many others prefer to let natural LAB strains do the work without intervention. Either way, the resulting process dramatically reduces the level of malic acid in the wine by converting it to lactic acid and another chemical called diacetyl which is a primary flavor and aroma component in butter. The specific strain of LAB used and the conditions in which ML takes place significantly influences the levels of lactic acid and diacetyl produced in the wine. Alternatively, winemakers can prevent ML from occurring by treating the wine with sulfur dioxide, keeping the pH below 3.3, or keeping the wine below 57º F among other methods. Winemakers may allow some barrels of wine to undergo ML while preventing it in others. When the winemaker blends the wine for bottling, they will combine wines from the ML barrels with wines from the non-ML barrels in specific proportions to produce the acid character and flavor balance they want in the finished wine. Highly skilled winemakers will carefully manage the ML and blending processes to produce outstanding wines with excellent balance and body; including Chardonnay made with 100% ML blends. Others, unfortunately, can be too heavy handed with ML, inoculating the wines with LAB strains that exaggerate the buttery character which dominates the wine, making it unbalanced and flabby.So, if you have been one of the many “ABC” wine drinkers, like me, that have snubbed Chardonnay because of the overuse of ML, give Chardonnay made by a wine maker that carefully manages the ML process another chance. You may be surprised just how complex and well balanced Chardonnay can be.


About the Author

Sam Schmitt, Csw - Sam is an avid wine enthusiast and professional wine educator living in Scottsdale, AZ. He is a Certified Specialist of Wine and Professional Member of the Society of Wine Educators. He is an active wine traveller and visits the wine growing regions of the U.S., Italy, France and Spain often. Sam is also a member of the Arizona Wine Growers Association and a vocal advocate of Arizona's developing wine industry.