Monday, March 12, 2012

Wine Education 411: Secondary [Malolactic] Fermentation

Previously, we learned about primary fermentation a few weeks ago, there is a secondary fermentation that takes place in a lot of red wines and big, bold, supple, oaky Chardonnays.  This second fermentation is called malolactic fermentation, or the conversion of malic acid (think green apples!) to lactic acid (the acid in milk!). 


Why does wine go through malolactic fermentation?  This is done to make the acids taste "softer" or less harsh to wine drinkers.  Most red wines go through malolactic fermentation.  Additionally, many Calfornian or very oaky Chardonnays are put through malolactic.  In comparison, many aromatic or light white wines (i.e. Riesling, Gewurz, New Zealand Sauvignon Blanc, etc.) do not go through malolactic fermentation.  These wines often taste more acidic and sour than their red counterparts.  [The acidity is part of the reason why we chill white wines before consumption!]

In Chardonnay, this secondary fermentation can also produce that buttery flavor that is characteristic of oaked Chardonnays.  This buttery flavor is a byproduct of the fermentation.  It is the same flavor compound that we use on movie-theater buttered popcorn!

(Photo from Google Images)

Many winemakers choose to inoculate for malolactic using a commercial strain of lactic acid bacteria (LAB) at the very end of primary fermentation.  The main commercial strain used for malolactic inoculation is called Oenococcus oeni (ee-no-kock-us ee-nigh).

Oenococcus oeni
(Photo from Google Images)

More traditional methods allow winemakers to wait for "spontaneous" or "natural" malolactic to take place.  Here, the native malolactic bacteria that come in on the grapes eventually start converting the malic acid to lactic acid without any aid of a commercial strain.  Many French producers still practice this method, but many premier red wines are also produced this way.  This can be a tricky process, however, because native LAB can be really picky on when they do (or do not) like to convert the acids.  Usually, barrels or tanks need to be warm and frequently monitored to make sure the LAB's are doing their job!  Such a task can be time consuming and costly, which is why many of these wines cost just a little bit extra.  :)

(Photo from Google Images)

The "new" malolactic fermentation method that is catching on is called co-inoculation.  This involves the inoculation of both the primary fermentation yeast strain (probably Saccharomyces) and the LAB.  Here, the LAB start converting the acid while the yeast are converting sugars to alcohol.  This allows for a quicker malolactic fermentation (it gets done near the end of primary fermentation if everything goes ok), and a different style of wine compared to the other 2 methods. 

(Photo from Google Images)

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