"True Facts" Malo what?

Right about now in the local wineries the fermentation process is over and many of the new wines are resting in barrels, tanks or bottles. But wait, that’s not all… as far as fermentation goes.

We all know that wild or commercial yeasts are put to work on the freshly picked grapes almost as soon as they come in from the vineyard. This is the primary fermentation stage where the grape sugars are consumed by the yeasts and converted into alcohol (and carbon dioxide); where grape juice becomes wine, essentially.

What happens next, for most red wines, as well as for selected white wines like Chardonnay, is that ANOTHER fermentation stage is initiated. And confusingly/maddeningly this stage is technically not about fermentation really, but about acid conversion.

 

What is often referred to as secondary fermentation process is called malolactic fermentation, with winemakers shortening the term to “ MLF” and tasting room hosts tossing it off as “Malo”.  In short, what happens in the wine is that the hard, green apple-like and tart malic acid is converted into softer, creamy, even butter-like lactic acid.

Malic acid is the primary acid component of apples (mālum in Latin = apple) giving them their delicious tartness. Lactic acid is the main acid in fermented dairy products like yogurt, (in Latin lac, lact- = milk) and it is much less tart in comparison.

You don’t want your Pinots or Cabernets to taste of green apple, but you just might like your Chardonnays to be creamy and buttery, so it is up to the winemaker to get this malolactic conversion going. Bacteria does the work here rather than yeast, specifically Oenococcus oeni (formerly Leuconostoc) bacteria (sometimes lactobacillus and Pediococcus). The bacteria, like yeasts, can be naturally occurring, but since the MLF process can be difficult to control, and in some cases difficult to start, winemakers often inoculate with commercially-prepared cultures. The MLF can still be a winemaker's headache and depending  on weather and cellar conditions, for example, it may not even be completed until spring!

  

In general, wines that are prevented from going through malolactic conversion have a high concentration of malic acid and therefore a perception of vibrant crispness and fresh fruit. Riesling is a wine that seldom is (and probably should NEVER be) allowed to undergo malolactic conversion. Riesling's high natural acidity is one of its desirable traits and core structure.

Wines that have gone through partial or complete malolactic conversion have a decreased perception of acidity, and have traded fruit and varietal aromas for fuller mouthfeel and a buttery flavor. A winemaker may choose only allow some of his, say, Chardonnay juice to go through MLF while leaving some juice with higher malic acid to add a vibrancy and balance to what otherwise might be a flabby and creamy wine. Some people like it that way. Who am I to judge? 

One more reason that many wines are allowed or made to undergo MLF is that you don't want this process to happen spontaneously in the bottle! A by-product of MLF is CO2 which would give the wine an unexpected (and unwanted) spritz and could push out the cork or burst the bottle.

So we know that Malic acid is exactly one of the components making an apple taste apple-y, but it is also interesting to learn that a by-product of the malolactic conversion called diacetyl, is exactly what makes foods from movie popcorn to margarine to actual butter taste buttery!

<Geek Alert>

Recent research hints that the conversion to lactic acid may release more than just a buttery character, but may also free up bound aroma compounds that are stuck to sugar molecules. Wine Aromas and MLF 

Otherwise trapped or glycosylated aroma compounds are released during malolactic fermentation which suggests that O. oeni can alter the sensory characteristics of wine through the hydrolysis of aroma precursors.

</Geek Alert>

Wow, the bound up aromas can't be smelled, but MLF bacteria work overtime to free them so they can waft to your nose.