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Winemaking: Malolactic fermentation

Dec. 23, 2021

Is it right for you and your wine? Maybe!

The ambition of most home winemakers is to make the best wine they can; something that can be enjoyed with pride and deserves recognition. In my opinion, it is natural and very human to want to be good at something. After all, who wants to spend time making an "average" wine that doesn't deserve recognition?


This desire to make exceptional wines has both advantages and disadvantages. It makes winemakers careful in everything they do, following strict instructions and so on. And it makes them eager to explore and experiment with different, more advanced techniques; something that helps make home wine a more interesting pastime.


That in itself is fine, but only if these advanced techniques are applied with care and complete understanding, otherwise one may find oneself in a quandary, so to speak. This is where the topic of malolactic fermentation fits into this discussion.


We often find home winemakers wanting to apply malolactic fermentation techniques to their wines simply because they happened to read about it somewhere and it sounded interesting. In reality, they were given only enough information to pique their interest, but not enough information to apply the task in a reasonable way. Essentially, they provided enough information to hang themselves.


While I will be the first to say that malolactic fermentation plays an incredibly beneficial role in the world of home winemaking, at the same time one must understand that it is certainly not something that can be applied whimsically to any wine. And it is definitely not a guarantee that you will have better wines. Its effects may or may not be to your liking, and it may not apply to the particular wine you are making. In some cases, it may actually ruin the wine.

Fermentation Tank


What is malolactic fermentation?

In very basic terms, malolactic fermentation (also known as MLF) is a process in which certain types of bacteria degrade the malic acid in wine into lactic acid and carbon dioxide gas. It is a very natural process that can occur spontaneously if the conditions are right - usually after yeast fermentation is complete.


It can last from a few weeks to three or four months, depending on.

✱ the amount of malic acid available in the wine

the conditions under which the fermentation takes place

✱ The power of culture


On average, you can expect MLF to last 3 to 6 weeks if a domesticated culture is added to the wine.


This spontaneous form of fermentation is largely limited to unpasteurized juices, as opposed to sulfite treated or pasteurized juices. The difference is that malolactic acid bacteria are not present in sterilized juice to multiply.


There are thousands of different strains of lactobacillus malicus. Some of them are better for wines than others. For this reason, wineries often choose to inoculate selected wines with known malolactic cultures, rather than hoping that Mother Nature will do the job herself to obtain satisfactory results.


How does malolactic fermentation affect wine?

Professional wineries often seek to perform this process in a given wine for one or more of the following reasons.

◬ To reduce the acidity of the wine.

The acidity of the must may be too high due to geographic climate, or it may simply be a bad, short season in the region. By inducing malolactic fermentation, the winemaker can reduce the overall acidity of the wine.


There are two reasons for this.


1. lactic acid does not taste as acidic as malic acid. Therefore, as malic acid converts to lactic acid, the wine's acidity decreases.


2. Not all malic acid is converted to lactic acid. Some is converted to carbon dioxide gas. Only about 2/3 of the malic acid is converted to lactic acid. The rest just turns into carbon dioxide gas and then disappears.


◬ Increasing the stability of the wine.

By inducing malolactic fermentation now, you can ensure that it does not occur later at a less convenient time - for example, after the wine has been bottled. Bottled wines that have undergone uncontrolled MLF often become cloudy, sometimes forming sediment with a slight carbonation and an odor very similar to sauerkraut. This risk can be eliminated by putting the wine through the MLF step under controlled conditions using selected strains of malolactic cultures.


There is very little risk of unwanted malolactic fermentation when making wine from packaged juices and concentrates. The issue of stability relates more to wines made from the grapes themselves. If MLF is not needed in a particular wine for other reasons (e.g., flavor), then stability can also be achieved by treating the wine with some type of sulfite.


◬ Alteration of wine characteristics and flavors.

The body and flavor of MLF-treated wines can also change, in part because lactic acid is softer and smoother compared to malic acid, and in part because of the various byproducts that result from this fermentation. Depending on the wine in question, these changes may or may not be welcome.


Wines that have undergone malolactic fermentation tend to be less fruity in flavor and aroma. This lack of fruitiness is mostly replaced by a deeper, richer, more complex character. The texture of the wines is often creamy and a slight butterscotch to vanilla flavor can usually be noted. This is due to the diacetyl produced during the MLF.


What types of wines should undergo MLF?

Based on the information provided above, you may begin to see why not all wines should be considered candidates for malolactic fermentation.


For example, wines made from fruits other than grapes, such as blackberries or cherries, should probably not be considered. After all, it is the fruitiness of these types of wines that sets them apart, and as mentioned earlier, malolactic fermentation can reduce this fruitiness. Treating fruit wines with MLF only erases the best assets of these types of wines. So in general, keep MLF away from wines made from fruits other than grapes.


This is also true for lighter, fruitier wines made from grapes such as Zinfandel or Liebfraumilch. These wines should not be affected by MLF. Doing so would only throw them out of balance and give them an unusual character - at best - to be perceived as unusual by the average wine drinker.


So, what kind of wines should be considered for malolactic fermentation? The answer is fairly straightforward. Consider a full-bodied wine that already has a strong, earthy character. The idea here is to consider only wines that already have some of the same characteristics produced by MLF so that they can be built or enhanced by the process.


This narrows most of the field down to big, heavy red wines. To help you understand, wines such as Pinot Noir, Merlot and Cabernet Sauvignon can do well with the additional influence of malolactic fermentation.


White wines are generally considered unsuitable for MLF, but a major exception to this rule is the Chardonnay grape. Wines made from this grape are often treated with MLF by commercial wineries in the United States and abroad. Chardonnay wines have the flavor intensity and body needed to handle the effects of malolactic fermentation.


I must point out here that this does not mean that all full-bodied red wines or Chardonnays should be MLF'd, nor does it mean that you cannot make great wines without the help of MLF. On the contrary, most home winemakers never deal with MLF and still regularly win tasting competitions, regional judging, and state and county fairs.

The fermentation tanks make by ZYBREW


When and how do you induce malolactic fermentation?


◬ When.

Malolactic fermentation is best done immediately after wine yeast fermentation is complete. When the gravity reading is 0.998 or lower, consider this the marker for when fermentation is complete. there are several reasons why MLF is best induced at this time rather than before or after.


Lactobacillus cultures are capable of consuming sugars like yeast. However, instead of converting these sugars into alcohol as yeast does, they slowly convert these sugars into volatile acids such as acetic acid; the acid that puts sharp wrinkles into vinegar. Therefore, we can conclude from this information that it is not a good time to induce MLF during yeast fermentation when the must still contains sugars.


Another thing to consider is that malolactic fermentation is more sensitive to sulfites than yeast. Therefore, if the must is treated with sulfites (such as Campden Tablets or sodium bisulfite) prior to fermentation - as you should be - the residual amount can easily interfere with the ability to initiate MLF. MLF can be safely initiated only after fermentation activity has resulted in the dissipation of all sulfites from the must.


MLF is very sensitive to sulfites, which is why it is important to induce and complete it before adding sulfites to stabilize the wine. Often, one will add sulfites again at the end of fermentation to reduce the chance of spoilage. This is not the case if you want to induce MLF. Do not add any sulfites until the MLF is complete.


The same rule applies to adding potassium sorbate. While MLF will occur in the presence of potassium sorbate, doing so will usually produce poultry odors, usually strong geranium to ripe fish flavors.


What does all this mean for someone who wants to get MLF when making wine from ingredient packs? First, they must realize that this will require them to deviate from the instructions provided and that not all instructions will be completed on the schedule provided with such kits.


The instructions for a home winemaking kit will usually tell you to siphon the wine into a clean container and add a packet of some sort of sulfite once fermentation is complete. Stop! After fermentation is complete and before adding any kind of stabilizer; this is when you want to induce malolactic fermentation. You can siphon the wine, but do not add any sulfites or other types of stabilizers.


Malolactic fermentation will occur over the next few weeks. Once completed, you will continue with the rest of the instructions as if nothing had happened.


◬ Method.

While one can try to rely on MLF to occur naturally, it's a bit like rolling the dice. There are countless strains of bacteria capable of converting malic acid to lactic acid. The problem is that these strains come with a variety of side effects. Some are pleasant, but most will cause defects in the wine. Also, there is always the possibility that MLF will not occur on its own at all. This makes inoculation with a known MLF culture the preferred method used by most wineries today.


The use of lactic acid bacteria cultures is very simple. If you want to inoculate 5 or 6 gallons of wine, simply pour the contents of the package directly onto the wine at the appropriate time. If you want to inoculate more than 6 gallons, you will need to use a fermentor so that the culture has a chance to grow larger.


The most difficult thing about making an MLF starter is that it needs to be started a few weeks before it is needed, if it is worth the effort. This requires a little thought on your part.


For every 10 gallons of wine to be inoculated, take 1 quart of apple juice and 1/4 teaspoon of Ghostex (yeast extract) and add it to a gallon jar or similar item along with a package of MLF culture and cover it with air - lock. The maximum we recommend to culture a package is 30 gallons. When it is time to use the culture, simply stir it into the wine. Again, the starter needs to be ready a few weeks before it is needed.


There are a few variables that affect the rate of malolactic fermentation. The first is temperature. Just like yeast fermentation, the wine should be kept between 70 and 75 degrees Fahrenheit. Temperatures lower than this will slow down MLF, and temperatures higher than this will promote the growth of harmful bacteria.


Wines with very high acidity (very low pH) may be difficult to ferment. Although this may seem ironic, some wines have acidity levels well beyond what can be corrected by malolactic fermentation. Although domesticated MLF cultures are more tolerant of lower pH, problems may be encountered in obtaining full MLF in wines with a starting pH of 3.1 or lower.


Wines with high alcohol levels (13% and above) may not support MLF. just like drinking too much acid, alcohol can inhibit MLF activity. While MLF may occur slowly in higher alcohol wines, appetizers should be considered to help improve the odds.


What happens after malolactic fermentation?

Once malolactic fermentation is complete, there are a few things that should be done before proceeding to the next step, or in the case of a home winemaking ingredient kit.


The wine needs to be siphoned into a clean container. This should be done with a splash in order to aerate the wine. Aeration is needed to help release the off flavors that often accompany MLF. After aeration is complete, you will need to add a sulfite, such as Campden Tablets or potassium bisulfite, to the wine. This is usually the next packet needed when making wine with the Home Winemaking Ingredients Kit.


After both aeration and sulfite are complete, you will need to check the acidity level of the wine to determine if additional acid is needed. Sometimes, MLF can excessively reduce acidity levels, causing wines to be tasteless and susceptible to infection during storage.


You can test your wine with the help of an acidity test kit. It will tell you if your wine is in the acceptable range and how much acid needs to be added if it is too low.

If you do need to add acid to your wine, you should use tartaric acid. If malic acid is used, this may trigger another malolactic fermentation. If citric acid is used, any remaining MLF culture will slowly convert the citric acid to acetic acid (vinegar). This also means that an acid blend should not be used to increase acidity. The acid blend contains malic acid and citric acid.


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