The super secret mysterious malolactic fermentation

by Winemaking

I went into a homebrew store close to my house today, because I needed some malolactic cultures for two red wines I am making.  The Denver Broncos had just been pounded in a football game they should have won, and I really didn’t want to drive the 20 minutes to my favorite homebrew store.

I asked the shop employee if they had any malolactic cultures.  He attempted to direct me to some of the Belgian sour strains for beer, but quickly surrendered and admitted he had no clue what I was asking for.  After a few minutes of explaining it was clear, despite their selection of wine kits and wine yeast, this was a “beer only” shop.  Defeated (like the Denver Donkeys) I got back to my car and drove to the better homebrew store.


After your wine fermentation is complete, you'll want to start a malolactic fermentation

What is malolactic fermentation?

Despite my experience, malolactic fermentation is nothing mysterious.  A malolactic fermentation, also known as MLF (not MILF – that is something else), is a fermentation where malic acid is converted by bacteria to lactic acid and CO2.  The bacteria used are usually Oenococcus oenii.  Other lactic acid bacteria include various species of Lactobacillus and Pediococcus.  Malic acid tastes like green apples and is tart.  Lactic acid however is smoother and slightly buttery to the mouth.  Lactic acid is present in sour milk.

The malolactic fermentation should occur after the initial fermentation and lasts for 3 weeks to 2 months.  This fermentation can happen naturally or with an added culture.  The problem with natural malolactic fermentation is many bacteria are capable of this task.  Some bacteria are better than others and bad ones can ruin the wine.  To produce a consistent wine, it is better to use a known culture rather than leave it up to Mother Nature.

Why should you do it?

There are several reasons to perform a malolactic fermentation on your wine.  The first reason is to reduce the acid level.  The reduced acid gives the wine the better mouth feel mentioned earlier.

A second reason is to stabilize the wine.  If you don’t undergo malolactic fermentation, your wine might undergo one spontaneously later in the bottle.  This will cause your wine to be fizzy (from the CO2) and most likely ruin the flavor.  The wine can also turn cloudy, and have a sour kraut aroma (that’s bad).

Another reason is the wine flavor is changed.  By-products from the fermentation will give the wine more body (from glucans and dextrans), a buttery flavor and mouth feel (from diacetyls), and other notes of vanilla, honey, nuts, or smoother tannins.  This gives the wine a much more complex and enjoyable flavor (that’s good).

Why you should not do it?

For some wines malolactic fermentation would produce a wine which is “out of style”.  For most white wines you want the higher acid.  Malolactic fermentation will make a white wine seem “flatter” because the second fermentation will always increase the pH.  Malolactic fermentation adds to the total time to produce your wine.  You have to delay adding sulfur dioxide to your wine as well, since it will kill the bacteria.

If you are making a sweet wine, malolactic fermentation will throw the flavor out of balance since there will be less acid.  A wine which had under gone malolactic fermentation will be less fruity in aroma and flavor.

Malolactic fermentations are best for big red wines such as Pinot Noir, Merlot, and Cabernet.  Chardonnay is one white wine exception, because the buttery flavors are part of the wine style.

When should you do it?

You want to add your malolactic culture at the end of your fermentation.  The reason is the bacteria can also process sugars, but will produce off-flavors.  You are adding the bacteria to consume the malic acid only.  The end of the fermentation is also best because the decaying yeast provides nutrients for the bacteria. Most cultures are 125 ml per 6 gallon batch.  To help accelerate the malolactic fermentation, leave your wine on the lees and occasionally gently stir the carboy.


Once the malolactic fermentation is complete, you need to aerate the wine and rack it to a new container.  The aeration helps drive off bad aromas from the second fermentation.  You will also need to add Campden Tablets or Potassium Bisulfite to the wine.  This is to stabilize the wine and help reduce any oxidation effects.

You should also test your wine acidity after the fermentation.  Sometimes the malolactic culture can go overboard and convert too much acid.  In this case you will need to add tartric (not tantric—that’s something else) acid to the wine.  Don’t add more malic acid since this might renew the fermentation.  Citric acid is also bad because the culture could convert the citric acid into acetic acid (vinegar).  Acid blend should also be avoided because it contains citric and malic acid, giving you a double whammy of bad problems.

Malolactic fermentations can give your wine new complexity.  It’s not intended for all wines but when done properly, the second fermentation produces a much smoother wine with better flavors.

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DJ Spiess

DJ Spiess

Beer buddy

I live in Denver, Colorado. This blog is everything about beer, wine, cider, mead and other spirits.
I am a avid homebrewer and winemaker. I’ve been making my own beer and wine for many years. I started making beer when I was in college (mostly because the drinking age in the United States is 21). My first few beers were horrible. The beers are much better now, and I often supply my neighborhood with free beer! It is a great hobby!