Wine Making: Malolactic Fermentation
Is Malolactic Fermentation Right For You and Your Wine?
It is the ambition of most home winemakers to make the best wine recipe they can; one that can be enjoyed with great pride and be worthy of recognition. As I see it, wanting to be good at something is only natural and very consistent with human nature. After all who wants to spend their time making a "just average" wine worthy of no recognition?
This yearning to make a remarkable wine has its benefits and downfalls alike. It causes the winemaker to be careful in all that they do, to follow directions closely and such. And, it gives them a passion to explore and try different, more advanced techniques; something that helps to make home wine making a more interesting pastime.
This is all well and good in of itself but only if these advanced techniques are applied with discretion and complete understanding, otherwise one may find themselves out on a limb, so to speak. This is where the subject of malolactic fermentation fits into this discussion.
Quite often we find home winemakers wanting to apply the technique of malolactic fermentation to their wines simply because they read about it in passing somewhere and it sounded interesting. In effect they were given just enough information to pique their interest but not enough information to apply the task in sound fashion. In essence they where given just enough information to hang themselves.
While I'll be the first to say that malolactic fermentation plays an incredibly beneficial role in the world of home wine making, at the same time one must understand that it is certainly not something that can be applied whimsically to any wine. And, it definitely does not guarantee that you will have a better wine. The effects that it has may or may not be to your liking, nor may it be appropriate for the particular wine you are making. In some cases it may actually ruin the wine.
What Is Malolactic Fermentation?
In very basic terms malolactic fermentation (also known as MLF) is a process where certain types of bacteria degrade the malic acid that is available in a wine into lactic acid and CO2 gas. It is a very natural process and one that can occur spontaneously if the conditions are right--usually after the yeast fermentation has completed.
It can last anywhere from a couple of weeks to three or four months depending on:
- The amount of malic acid available in the wine
- The strength of the culture, and
- The conditions under which the fermentation is being performed.
On average, you can expect an MLF to last 3 to 6 weeks if a domesticated culture is added to the wine.
A spontaneous version of this fermentation is limited for the most part to juices that have not been sterilized as opposed to juices that have been subjected to sulfiting or pasteurization. The difference being that a malolactic bacteria is not present to flourish in a sterilized juice.
There are thousands of different strains of malolactic bacteria. Some of them have better effects on a wine than others. For this reason wineries will usually elect to inoculate a selected wine with a known malolactic culture instead of hoping Mother Nature will do the job to satisfaction on her own.
How Does A Malolactic Fermentation Affect A Wine?
Professional wineries will often seek to have this process occur in a given wine for one or more of the following reasons:
To Add Stability to Wine
By inducing a malolactic fermentation now it insures that one will not occur later at a less convenient time--like after the wine has been bottled. Bottled wines that go through an uncontrolled MLF will typically become cloudy, sometimes forming a sediment, and be slightly carbonated with an odor that is remarkably similar to sauerkraut. By taking a wine and putting it through the paces of an MLF, under controlled conditions with a selected strain of malolactic culture, this risk is eliminated.
The risk of having an unwanted malolactic fermentation is very small when making wine with packaged juices and concentrates. The stability issue is more of a concern with wines made from the grape itself. If an MLF is not desired in a particular wine for other reasons such a flavor, then stability can also be achieved by treating the wine with a sulfite of some type.
To Lower the Acidity of Wine
A grape juice may be too high in acid due to geographical climate, or maybe it was just a bad, short season in that area. By inducing a malolactic fermentation the winemaker can reduce the overall acidity of the wine.
There are two reasons for this:
- The lactic acid is not as acidic to taste as malic acid. So, as the malic acid is converted to lactic acid the acidity of the wine lowers.
- Not all of the malic acid is being turned into lactic acid. Some is turned into CO2 gas. Approximately only 2/3 of the malic acid is turned in to lactic acid. The rest simply turns in to CO2 gas and goes away.
To Alter the Character and Flavor of Wine
Wines that go under an MLF will also change in body and flavor, partially due to the softer, smoother character of lactic acid verses malic acid, and partially due to the various by-products that can come off of this type of fermentation. These changes may or may not be welcomed depending on the wine in question.
Wines that go through a malolactic fermentation tend to be much less fruity in flavor and aroma. This lack of fruitiness is mostly replaced with a deeper, richer, more complex character. The texture of the wine is often creamy and a slight hint of buttery to vanilla flavor can often be noticed. This is due to the diacetyl that is produced during an MLF.
What Types Of Wines Should Be Subjected To MLF?
Based on the information given above you might be starting to see why not all wines should be considered candidates for a malolactic fermentation.
For example, wines made from fruits other than grapes such as blackberries or cherries probably should not be considered. After all it is the fruitiness of these types of wines that make them distinct, and as stated earlier malolactic fermentations will reduce this fruitiness. To treat fruit wines with an MLF would simply wipe out the best asset these types of wines have. So in general keep MLF's away from wines made from fruits other than grapes.
The same goes for lighter, fruitier wines made from grapes such as Zinfandel or Liebfraumilch. These wines should not be subjected to MLF. To do so would only bring them out of balance and give them a character that would be considered unusual--at best--by the average wine drinker.
So, what kind of wines should be considered for malolactic fermentation? The answer is fairly straight forward. Consider full-bodied wines that already have some rich, earthy notes to them. The idea here is to only consider wines that already have some of the same characters that an MLF produces so that they can be built upon or enhanced by the process.
This narrows down the field for the most part to big, heavy red wines. To help give you an idea, wines such a Pinot Noir, Merlot and Cabernet can do quite well with the added influence of a malolactic fermentation.
White wines are not usually consider appropriate for an MLF, however one major exception to this rule is the Pinot Chardonnay grape. Wines made from this grape are often treated with MLF by commercial wineries both in the U.S. and abroad. Chardonnay wines posses the flavor intensity and body required 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 subjected to MLF, nor does this mean that you can not make an exceptional wine without the aid of MLF. To the contrary, most home winemakers never deal with MLF and still win at wine tasting competitions, at regional judgings, and state and county fairs on a regular basis.
When And How To Induce A Malolactic Fermentation
When To Induce A Malolactic Fermentation
Malolactic fermentations are best done right after the wine yeast fermentation has completed. Think of it as something you tag on to the end of the fermentation, when the gravity reading is .998 or less. There are several reasons why MLF is best induced at this time and not before or after.
Malolactic cultures have the ability to consume sugars just like yeast. But, instead of turning these sugars into alcohol--like yeast does--they slowly convert these sugars into volatile acids such as acetic acid; the same acid that puts the sharp pucker in vinegar. So, one could conclude just from this information that during the yeast fermentation, when there is still sugars in the must, is not a good time to induce MLF.
Another thing to consider is that malolactic fermentations are even more sensitive to sulfites than yeast. So, if the must is treated before fermentation with sulfites such as Campden Tablets or Sodium Bisulfite--as you should--lingering amounts could easily interfere with the ability of an MLF to start. Only later, after the fermentation activity has caused all of the sulfites to dissipate off the must, is it safe to start an MLF.
The fact that MLF is very sensitive to sulfites is also the reason why it should be induced and completed before sulfites are added to stabilize the wine. Typically one would add sulfites again at the end of fermentation to reduce the chance of spoilage. Not so if you want to induce MLF. Hold off adding any sulfites until the MLF has completed.
The same rule applies to adding Potassium Sorbate. While an MLF can occur in the presence of Potassium Sorbate doing so will often produce a fowl odor, usually a strong geranium to ripe fish smell.
What does this all mean for someone wanting to have an MLF when making wine from ingredient kits? First off they must realize that it will require them to deviate from the directions that are provided, and that not all of the directions will be completed on the time table that is provided with such kits.
The home wine making ingredient kit's directions will typically tell you that once the fermentation has completed to siphon the wine into a clean container and add a packet of sulfite of some kind. Stop! After the fermentation ends and before a stabilizer of any kind is added; this is when you want to induce a malolactic fermentation. It is okay to siphon the wine but do not add any sulfites or other types of stabilizers.
The malolactic fermentation will occur over the next several weeks. After it has completed you will continue on with the rest of the directions just as nothing happened.
How To Induce A Malolactic Fermentation
While one could try to depend on an MLF to come along naturally it is a bit like rolling the dice. There are an endless number of bacteria strains that are capable of converting malic into lactic. The problem is that these strains come with all sorts of side-effects. Some are pleasant, but most bring defects to the wine. And, there is always the chance that an 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. For more information, see our Malolactic Culture.
Malolactic culture's use is very simple. If you are wanting 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 are wanting to inoculate more than 6 gallons a starter will be required so that the culture will have a chance to increase in size.
The most difficult thing about making an MLF starter is that it needs to be started a couple of weeks before it is needed if it is to be worth the effort. This requires a little forethought 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 extractive) and add it along with the packet of MLF culture to a gallon jug or something similar and cap it with an air-lock. The most we recommend culturing up a single package is 30 gallons. When it comes time to use the culture simply stir it into the wine. Again, the starter needs to be prepared a couple of weeks before it is needed.
There are some variables that effect the rate of a malolactic fermentation. First and foremost is temperature. Just like a yeast fermentation the wine should be kept between 70 and 75 degrees F. Temperatures cooler than this will slow the MLF. Temperatures warmer than this will promote unwanted bacterial growths.
Wines that are extremely high in acid (very low pH) may have a hard time fermenting. Ironic as this may seem, there are some wines that have acidity levels that are simply to far out of range to be corrected with a malolactic fermentation. While domesticated MLF cultures are more tolerant of lower pH levels, you may have problems getting a complete MLF in a wine with a starting pH of 3.1 or lower.
Wines that are high in alcohol (13% and above) may have problems supporting an MLF. Just like having too much acid, the alcohol acts as an inhibitor to MLF activity. While it is possible for an MLF to occur slowly in wines with higher alcohol, one should consider making a starter to help better the odds.
What To Do After The Malolactic Fermentation
Once the malolactic fermentation has completed there are a few things that should be done before bottling, or in the case of home wine making ingredient kits, before moving on to the next step.
The wine will need to be siphoned into a clean container. It should be done in a splashing manner so as to aerate the wine. Aeration is needed to help release unwanted odors that often come with an MLF. Once aeration is complete you then will need to add sulfites such as Campden Tablets or Potassium Bisulfite to the wine. This is usually the next packet called for when making wine from an home wine making ingredient kit.
Once aeration and sulfiting both have been completed you will then want to check the acidity level of the wine to determine if any replenishment of acid is needed. There will be times when an MLF will lower the acidity too much, causing the wine to be insipid and susceptible to infection while in storage.
You can test the wine with the aid of an Acid Test Kit. It will tell you if your wine is in an acceptable range and how much acid to add if it is too low. You can find our Acid Test Kit here.
If you do need to add acid to the wine, tartaric acid should be used. If malic acid is used this could trigger another malolactic fermentation. If citric acid is used any remaining MLF culture could slowly convert the citric acid in to acetic acid (vinegar). This also means that Acid Blend should not be used to bring up acid levels. Acid Blend contains both malic and citric.
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