Lactic acid bacteria responsible for converting malic acid to lactic acid during malolactic fermentation.

Creative Commons Photo by: GrahamColm

Malolactic fermentation is often associated with red wines and some Chardonnays. Specifically “buttery” Chardonnay. But what is it?

As the name implies it is a form of fermentation. Unlike a yeast fermentation, however, during malolactic fermentation no alcohol is produced.

Instead malic acid is converted into lactic acid by lactic acid bacteria. Clever name I know.

How Malolactic Fermentation Works

Just like yeast, there are lactic acid bacteria all around us and the grapes that we make into wine. Not all species, however, will produce a drinkable wine. There are only about four species we trust.

Thus to initiate a malolactic fermentation it is best to purchase a lactic acid bacteria specifically suited for the job. These can be found at many winemaking supply stores.

After primary fermentation is complete you inoculate your wine with the bacteria. It is important to prevent oxygen from coming into contact with your wine during this process as the bacteria only produce desirable results when they work anaerobically (without oxygen).

In simple terms the bacteria consume malic acid and convert it to lactic acid and carbon dioxide. There are a few reasons this is a good idea.

Why Should I do a Malolactic Fermentation?

Great question. More can be understood if we talk about the chemical process that your wine undergoes.

First of all there’s the issue of stability. The presence of malic acid in our wines makes it a breeding ground for good and bad lactic acid bacteria. If you don’t do a malolactic fermentation prior to bottling it could happen later once it’s in the bottle.

I once purchased a bottle of wine that underwent a malolactic fermentation after I bought it. The bottle blew out the cork making a holy mess. Not only that, what wine was left over tasted terrible. It was cloudy, bubbly, and lacked any of the flavors we bought it for.

The second reason to go through this process is to reduce acidity. Lactic acid is a less potent acid than malic acid. In general the acidity of a wine may be reduced by 0.1-0.3%. This may not sound like much but it is enough to taste a difference.

Speaking of taste, this is the third major reason for doing a malolactic fermentation. Malic acid is said to have a tart taste to it, similar to the peel of a green apple. Lactic acid, on the other hand has a buttery or milky flavor to it.

Lactic acid is also present in milk and other dairy products. In fact lactic acid is often referred to as “milk acid”. If you’ve ever heard a Chardonnay described as buttery, it has likely undergone malolactic fermentation.

Like a yeast fermentation a malolactic fermentation can get stuck. This can be caused by fermentation temperatures that are too low. Also, too much sulfur dioxide in your wine can prevent them from working their magic.

There are chromatography tests you can do to see if fermentation has completed. We’ll get into exactly how to do all of this in a future post.

The important things to know about malolactic fermentation is that it is the process by which lactic acid is produced from malic acid. It reduces acidity and gives wine a buttery or dairy taste. Some effect on mouthfeel can be noted as well.

Want More?

If you’re interested and you have a mind for chemistry I did find some interesting resources throughout the course of my research. They are pretty intense so brace yourself.

Malolactic Fermentation in Wine from Lallemand

This is a collection of scientific papers written by many PHds. Invaluable I’m sure if you can digest all the chemistry terms they throw around.

The Joy of Malolactic Fermentation by Ellen Butz of Purdue University

This is a PDF of a presentation on malolactic fermentation. There is a terrific graphic on page 14 that explains the optimal conditions for this bacteria to successfully convert malic to lactic acid. If you want to avoid this fermentation then staying away from the optimal zone is a great idea.

Link to above photo.