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Malolactic Fermentation (MLF)

Wine Making 201

If you have ever made wine from fresh grapes or from fresh grape juice (not Welches frozen concentrate) late winter becomes an interesting time of the year. Your wine has been in the secondary for several months and is nice and clear. Not much is going on...the holiday season is over, the grapes from the southern hemisphere have not yet arrived (Chilean grapes and juices) and you begin thinking about filtering and bottling your wine.

This is the time of year that something interesting can happen to your wines. If the acid has a good amount of MALIC acid and fairly low amounts of sulfite, AND the temperature of your cellar goes up a few degrees, Malolactic Fermentation (MLF) can begin. That's the MLF you occasionally see in the winemaking publications and books you may have read.

This can be a good thing given the right circumstances. If your wine is a bit high in acid, the MLF will reduce the acid by converting the harsher MALIC acid into the softer LACTIC acid. It happens when bacteria that is naturally in your wine wakes up and begins a new kind of fermentation. You may find that your wine is nice and clear, but there is a low level fermentation activity in you air lock. You may also see a fine band of bubbles around the neck of your carboy. If you shake the carboy, you WILL blow off a bit of carbonation! During this fermentation, the wine will of course have a reduced titratable acid level AND it may take on a slight buttery/butterscotch aroma and flavor. A nice combination for a Chardonnay!

Now for the bad things that can happen… While your cellar is nice and cool, the MLF is suppressed. If you get a bit anxious and decide to bottle BEFORE the MLF begins, and you have lower levels of sulfite, the right conditions for MLF, there are two possible results; if the MALIC acid levels are low, you'll find you have sparkling wine, kind of like Champagne. Not a bad thing if that's what you like.

If the MALIC acid levels are pretty high, the excess carbonation could result in the corks popping out or the bottles exploding.

Last night, I drew some wine out of the Chilean wines I made from fresh juice last year. I wanted to sample them and to decide if they were ready for filtering, final conditioning, and bottling. The Muscato and the Syrah turned out to be ready for their final processing, but I found the Chardonnay was in the middle of MLF! Nice and clear, but there was active low level fermentation and a small white halo of tiny bubbles around the neck of the carboy. My notes reminded me that the Chardonnay was a bit tart, so the MLF was a welcomed surprise!