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Home Winemakers Guide to Malolactic Fermentation

Home Winemakers Guide to Malolactic Fermentation

Malolactic fermentation is not a hard thing, and it’s not even an uncommon thing, but it’s something that many home winemakers do without really understanding why.  Malolactic fermentation, called MLF because it’s way less of a mouthful, is a secondary fermentation method used by commercial wineries large and small to naturally lower the acidity in many red wines and some whites, and can enhance the complexity and soften the mouthfeel.  This week, you’ll get a crash course in MLF and some basic guidelines to determine whether or not you should do a malolactic fermentation on your latest wine, be it from a wine kit or a home grape harvest. 

Anderson Valley Pinot Noir Red Wine Fermentation

What Is MLF?

MLF is probably where the term ‘secondary fermentation’ actually came from.  Much of our lore in the beer world stemmed from what wine making and home wine making was when the concept of home brew came around, which is probably why the antiquated concept of a 'secondary fermentation' on your beer came around.  With wine, mead and even cider, there are things happening at this stage that aren’t happening when you’re making beer, which is why you’ll always hear us refer to it as ‘bulk aging’ instead of secondary when we refer to home brew and beer making.  

Malolactic fermentation is an actual fermentation, of a sort.  You are introducing a bacteria called oenococcus oeni after the initial fermentation is done and all of the sugar has been converted, in a secondary vessel off of the yeast (called the lees in wine making) of course.  While oenococcus oeni will happily eat sugar, at this stage it’s more interested in malic acid because it’s the only food available, and will convert 2/3 of that malic acid into the softer lactic acid, reducing the acidity.  The rest is converted into CO2.

This will do a few things for your wine, including raising the pH (hence lowering the acidity) and adding a softer, rounder and more pillow-y mouthfeel.  It can also increase the overall complexity of bolder, dryer reds by reducing the fruitiness and enhancing some of the earthier fruit characteristics.  Malolactic bacteria also produces a fair amount of diacetyl, which is an off flavor in the beer world, but creates different effects in wine.  Diacetyl gives Chardonnay that distinct buttery flavor, but adds a round complexity to reds, helping accentuate some of the more subtle characteristics of the grapes.

Cabernet Sauvignon in the Northern Nevada Hills

How Do I Know If MLF Is For Me?

That’s a great question that doesn’t really have an easy answer.  The issue here is that you really need to taste and titrate your wine before you make a decision.  Yes, there are definite benefits to a malo fermentation with a Chard or Pinot, but if it doesn’t need it to be an incredible wine, and your acids are on point, then why?

There are definite signs that you can use to decide if you should initiate a malolactic fermentation.  One main reason to do it is if you are spontaneously fermenting, meaning that you are taking a page from the Anderson Valley and fermenting your Pinot with the yeast already on the grapes, and are worried about MLF happening no matter what you do.  Many home winemakers can accidentally have a malolactic fermentation in their wine in this case, which can lead to having less control of the bacterial species performing the fermentation, and therefore less control over your finished flavor.  If unanticipated, this can also lead to accidentally sparkling wine in the bottle!

Another is if you have a wine that has a tart taste or titrates super acidic, and you need to mellow it out.  There are chemicals for this, but chemicals can pose problems all their own, and a natural process for less acids and a higher pH can be very attractive if it will only benefit the wine more - which it will.  A third reason, and let’s be honest here, is if you think that your wine would benefit, and you just want to try it!  All part of the fun of home winemaking.

 Pre alcoholic fermentation of red wine cabernet sauvignon

Basic Guidelines for MLF

Most dry red wines tend to undergo MLF, as well as many traditional ciders,and white wines like chardonnay and sauvignon blanc.  There are a few basic guidelines to perform your own Malo fermentation, and one of the biggest is that you’ll want to let alcoholic fermentation finish first.  Oenococcus oeni is one of many types of lactic acid bacteria, and is perfectly happy to eat sugar instead of malic acid, which can create acetic acid, our favorite vinegar flavor.  This is why you don't see MLF in sweeter whites like Riesling or Muscat.

If you are using potassium metabisulfite or sodium metabisulfite during your transfer to stave off oxidation, remember that Oenococcus oeni is EXTREMELY sensitive to free SO2 in solution, so you’ll want to make sure that you let the campden tablets or sulfites wear off before you add your malo!

The next guideline is to test your pH and titrate your wine.  Our favorite LABs (lactic acid bacteria) are generally pretty ethanol tolerant, but prefer a pH of 3.4 to 3.5.  Many winemakers will try to start in the 3.4 range, assuming they’ll end closer to 3.5 when it’s all over.  Most oenococcus oeni strains will stall and have some issues performing starting at 3.2 pH and below.  If your TA (total acidity, generally measured in tartaric acid) is too high, then you know you’re on the right track.  If it’s not too high, but you want the added flavor and complexity of MLF, then you’ll have to add additives like tartaric acid after to lower your TA back into the range that you want.

The last is temperature.  Malolactic cultures have a fairly wide range, beginning around 59° F, but don’t move very fast at that temp.  They can go all the way to 98° F, but let’s be honest.  As home fermenters, we’re not going to subject our fermentation to anything that high unless it’s with a Kveik yeast strain!

The sweet spot is somewhere between 68° and 75° F.  This will give them the opportunity to work at moderate speed without getting too crazy, and you won’t have to worry about bench pressing your wine with elevated temperatures.  Plus, room temp is pretty convenient, even in cooler climates, so it’s kind of win-win.

Pitch a healthy culture, either White Labs WLP 675 or Wyeast 4007.  Both of these are a fantastic liquid strain of Oenococcus oeni, and are already pre-measured for up to 6 gallons, making them easy to pitch into your fermenters.  If you have some serious volume, then use Viniflora’s CH35, a wonderful freeze dried strain that comes in a package that is suitable for up to 66 gallons!

Malo-lactic Cultures MLF bacteria

How Long Should I Wait For MLF to Finish?

If you’re in a cool climate and your fermenter is in the low 60’s, then expect your MLF to take longer, but according to White Labs, the rule of thumb is that these guys will take 4 - 6 weeks to finish the job.  From here, you can add sulfites (if you like that sort of thing) and rack to another bulk aging container and begin the initial aging process.

All of that being said, definitely test your TA and pH before you get too crazy.  You can expect a typical malo fermentation to raise your pH by 0.2% to 0.4%, which is a good way to tell that it’s done it’s job.  You can also compare your original TA reading to the finished reading to get a good idea of how much malic acid was converted.  

This article acts as a baseline for your malolactic fermentation experience, but if you have any questions about O. oeni, process, expectations, or even adding malo to a cider, post them in the comments below!  We’d love to hear about your experience performing MLF, too!

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