What Exactly is Malolactic Fermentation???

Wine geeks and professionals often use terms that can be difficult for the casual consumer to understand.  Usually, though, at least the major point of the words, can be broken down pretty simply.  One example of that is malolactic fermentation, which I'm going to try to break down pretty simply and then at least at an introductory scientific level.

The easiest way to understand malolactic fermentation is to actually look at the words themselves.  Fermentation is the action of yeast converting sugar into alcohol and carbon dioxide, at least at the most basic level that most of us drinkers need to/want to know about.  The reality of it is, much like our own digestive process, or any other chemical reaction, there's a lot more going on.  In the case of malolactic fermentation, one of the results is the conversion of malic acid into lactic acid.  Hence the name malolactic fermentation.  Malic acid is the tart acid which tastes a lot like a green apple or tart pear.  Lactic acid is the acid found in milk, butter, and other dairy.

So, on its most basic level, malolactic fermentation is fermentation which turns tart, apple-like acids into creamy, buttery, acids.  Chardonnay is the varietal where this simple breakdown is most evident, and most easy to understand.  On the other hand, malolactic fermentation is either desired, or not desired, in many other varietals, which neither start out with such a sharp green apple taste, or end up quite as buttery as many chardonnays do.

The Science Behind It
Malolactic fermentation usually uses one or more of three different types of bacteria, Oenococcus oeni, Lactobacillus, and Pediococcus.  Each of these bacterias eats up tart malic acid and spits out lactic acid and diacetyl.  Lactic acid provides a smooth, creamy, round flavor and mouth feel, and diacetyl, which is often considered a fault in both beer and wine, provides a buttery flavor and aroma (think movie theater popcorn).

Again, Chardonnay is the most extreme example, but most red wines, and many whites, undergo some malolactic fermentation.  The original flavor profile of the wine, the environment in which malolactic fermentation occurs, and many other factors affect how obvious the flavor effects are on a wine.  On the other hand, many crisp, tart, fruity, and floral whites are produced in such a way as to almost eliminate the possibility of malolactic fermentation, in order to preserve the sharp acidic notes in the wine.

Malolactic fermentation can occur either as part of the primary fermentation, or after the wine has been fermented.  It can and does occur naturally, or the bacteria can be deliberately introduced.  It is almost always done either during fermentation or aging, and almost never in the bottle.  One increasingly rare exception is certain Vinho Verdes from Portugal, which underwent malolactic fermentation in the bottle, since slight effervescence is expected in the wine.  This is less popular now, as wines which undergo fermentation in bottle also throw a sediment and pour less clear.

Hopefully this post helps a few people understand a little more exactly what malolactic fermentation means, and more importantly, why they should care about it when buying or drinking wine!