Malolactic Fermentation

by Dave Salaba

Malolactic (pronounced MAH-low-LACK-tick) fermentation has been a hot topic among winemakers, as well as in university circles, for decades. Literally hundreds of papers and several books have been written on the subject and more are being presented all the time. Malolactic fermentation (called MLF for short) has been a part of winemaking (although probably unknown to early winemakers) for centuries. Almost all well-made red (and a few white) wines, from every region in the world, are subjected to MLF. There are exceptions, of course, but vintners usually favor the smoother, more pleasant, and fuller mouthfeel it produces. Suffice to say that serious (and even silly) winemakers should know at least a little about MLF.

The term malolactic comes from the process whereby the sharp-tasting malic acid contained in grapes (and wine) is converted into a smoother, softer-tasting acid called lactic acid. Malic acid is found in apples, and gives them their sharp, tart taste. Lactic acid, on the other hand, is a softer, smoother-tasting acid that can very positively affect the “mouthfeel” of our wine without making it flabby and out of balance. This process appeals to winemakers around the world because it allows them to produce wines that have sufficient acid to stand up to foods with fat content without being unpleasantly acidic.

MLF also creates a buttery richness by producing diacetyl (pronounced die-AH-seh-teel).You’ll recognize diacetyl because it is used on popcorn-it’s that “popcorn” smell when you go to the movies. In small amounts, this buttery characteristic is highly desirable in red wines, as well as a few whites, such as chardonnay.

Finally, MLF can also help stabilize and protect your wine against spoilage by lowering the acid in your wine and eating the nutrients that could feed organisms that create spoilage.

MLF is conducted by a special kind of bacteria. These little buggers are part of a very large class of bacteria known as lactic-acid bacteria. Other kinds of lactic-acid bacteria are used to make sauerkraut, pickles, and yogurt, but these are hardly the flavors or aromas that you would want in your best wine. Thus, our MLF will be conducted in a controlled manner using a specially formulated ready-to-use culture, available at Keystone Homebrew Supply.

Malolactic bacteria are a little fussy about their conditions. They aren’t tolerant of high alcohol (above 14%), high sulfur dioxide (above 20 ppm), low temperatures (below 64°F), high acidity (pH below 3.2), and high levels of oxygen. Before you say, “Wow, this sounds complicated,” be assured that for most home winemakers the conditions that favor yeasts will also favor malolactic bacteria, so most of these will be taken care of as part of your regular winemaking. The key points about MLF that you’ll want to remember:

1. stick to a modest pre-fermentation use of metabisulfite (¼ to ½ tsp. per 5 gal. of must)
2. keep the temperature above 64°F
3. wait until the sugar is below 4° Brix before starting MLF

Wines made from grapes respond best to MLF. The main reason is that the bacteria work better with a small amount of grape solids to feed on in addition to the malic acid. Wine kits do not need MLF because they are formulated with malic acids. We recommend against using MLF with any wine kits because it reduces the acid levels too far and leaves the wine unbalanced.

We recommend adding the malolactic culture after primary fermentation, although a few wineries add it earlier depending on acid levels and their production schedule. For most of us however, the best time to add a MLF culture is when the sugar reads “zero” on the hydrometer.

Malolactic bacteria work more slowly than yeasts, so it may be difficult to know if they are working. Generally, the gas bubbles escaping from the airlock should increase after the MLF has started. If you are using a glass fermenter, another way to tell is to take a strong flashlight and, after darkening the room, hold the lighted flashlight at an angle near the neck of the carboy or bottle. You will see tiny bubbles making their way to the top if you observe for a minute or so.

The slow malolactic fermentation can take as long as three months, so be prepared to be patient. As the saying goes, “you may be done with the wine, but the wine isn’t done with you!” If you want to be sure that the MLF has finished, we carry test kits that can confirm MLF.

Remember, if you have any questions about MLF, don’t worry! We at Keystone are here to help, and we want you to be successful at making better wines! We have many years of experience in winemaking, so we encourage you to call or stop by with any questions about MLF or winemaking.