Editor’s Note: For convenience, we’ve created a collection of all current cider articles by this author.

By Michael Wilcox

Look, Judges don’t need to know all of this. As an organization largely serving North American homebrewing competitions, MLF in homemade cider is encountered quite rarely by BJCP Judges. (At least, encountered intentionally.) But if one is interested, here’s a bit of what I know about this incompletely-understood topic. Some of this is oversimplified by necessity, and there is more information out there if you want to keep learning. I myself have much left to learn. The other function of this article is to get ahead of some of the misinformation out there, such as “Use 71B; it’ll perform MLF.” Just as with Beer and Mead, having an understanding of how styles of cider are made and how they develop their specific characters will make your review more useful to the entrant. Judges need to know how to fully describe the cider, decide where it does and does not fit a guideline, and how big a deal those “misses” are. Understanding the basics of malolactic fermentation can help with that.

What is it?

Malolactic fermentation is the conversion of one molecule of malic acid (C4H6O5) into one molecule of lactic acid (C3H6O3) plus one molecule of carbon dioxide (CO2). In addition to a slight increase in carbonation, MLF alters the balance of the cider by reducing acidity, removes nutrients, and may present significant flavor and aroma changes. The exact changes occurring during MLF will depend on the organism performing the MLF, and what conditions the cider is experiencing.

What performs it?

MLF is not performed by the beer or wine yeasts** we pitch to make cider, but rather by Lactic Acid Bacteria (LAB). Beer judges are probably already familiar with some of these. The three main classes of LAB that perform MLF are Pediococcus, Oenococcus, and Lactobacillus. To my knowledge Pedio has no positive effects and isn’t welcome in a clean cider. I’m willing to believe there could be a positive flavor contribution but for now we have zero sour cider styles anyway, so we’ll consider all the species of Pediococcus to be spoilage LAB until shown otherwise. You may seen vials of have Oenococcus oeni available in a home winemaking shop – most red wines and some white wines undergo MLF. There is only one Oenococcus species but several strains available. The third class of LAB, Lactobacillus, has several species common in cider and is what creates the phenolics we associate with the BJCP English Cider style and to a lesser extent French Cider.

**A word about 71B. I often hear this yeast described as a strain that “does a partial MLF” – in truth this yeast (and a few others) simply metabolizes a portion of malic acid. It is not performing malolactic fermentation, it is not creating lactic acid, and it is not creating the spicy/smoky phenolics, but rather simply reducing acidity. 71B is not going to turn your New World cider into English. I find this strain quite useful when making New World Ciders using very acidic, crab-heavy blends. In low acid blends I find it reduces acidity to levels I no longer find refreshing without adjustment. Your palate may vary.

When/under what conditions does it happen?

Lactic acid bacteria are inhibited by high alcohol, low pH, low temperature, lack of nutrients, high relevant acid concentrations, and presence of bound and especially free sulfites.

Alcohol high enough to inhibit MLF really doesn’t happen in cider without a lot of added sugar – for instance a very big Applewine or New England Cider. Varying by strain but generally in the range of 13% ABV, inhibition of MLF by alcohol is really more of a grape wine issue.

Temperature of 60F is low enough to keep most strains from starting, though I’ve found it will continue at this temperature if it has already begun. Lactic Acid Bacteria like the 60F-75F temperature range, with some variation between individual strains. MLF in low temperature cider can take months to complete.

Generally pH below 3.2 will keep MLF from beginning, and many strains are at least somewhat inhibited below 3.5. Oenococcus generally works at lower pH than Lactobacillus and Pediococcus, making it ideal for wine and cidermakers looking to reduce acidity without added phenolic characters.

Malolactic fermentation *can* be performed at any time and some winemakers use this tool during primary, however most of the MLF I’m aware of in cider is performed after primary fermentation is finished – LAB can also metabolize sugars as yeast do, creating things like acetic acid that we want to avoid in a clean cider. This is one area where a sour cider would likely differ from those we have current guidelines for.

Leaving the cider on a small amount of the lees can help encourage MLF as nutrients necessary for LAB to perform are liberated as the lees are broken down. Extremely high levels of malic acid can create an environment that inhibits LAB, while high levels of lactic acid may kill LAB – as always sensitivity can vary significantly by strain.

Some sulfite will be Bound to the phenolics, acetaldehyde, and sugars in the cider, while the rest of the sulfite will be Free. The relative concentration of the different forms of sulfite will depend on the cider pH, with Free + Bound representing Total sulfite. Let’s save details about sulfite until the next article and simply say that generally LAB will be inhibited by more than 10 ppm Free and 30 ppm Total sulfite.

What effects does it have?

All classes of LAB will perform the same basic transformation of malic into lactic acid, but will differ in their other effects. As just mentioned, effects will also differ based on the conditions of the beverage.

Acidity Reduction

Complete reduction of malic acid will reduce the acidity by half if no other acids are present, i.e. malic % is in the high 90’s. If other fruit are used, i.e. acids other than malic are present in significant amounts, the reduction will be less.

pH Increase

Note that in a highly malic cider the pH increase can be significant. Cidermakers strive to keep pH low enough (<3.8) to help protect the cider from microbial contamination and may monitor the increase.

Acid Flavor

Recall that malic is considered to have a harsher flavor than lactic, thus cider with lactic acid often seems smoother, less metallic, and more approachable, not just simply less acidic.

Reduction of the base fruit character – You may be used to MLF changing fruit characters in wine; think of the complex aroma of some big reds that have gone through MLF versus the extremely fruity or floral nature that is the defining characteristic of most non-MLF whites – you wouldn’t want MLF ruining your Gewürztraminer aroma. Expect cider that has experienced MLF to have lower amounts of overt apple and perhaps a more nuanced fruit character. I generally find it more complex though some others have described cider post-MLF as “one-note”.

Phenolic Flavors and Aromas

Spicy, smoky, restrained barnyard. Think about the wines you have had – The kinds of phenolics we associate with, say, English Cider would be unwelcome at anywhere near this level in the vast majority of wines. Thus winemakers use Oenococcus oeni which is mostly associated with acid reduction without phenolics. Cidermakers are counting on getting the smoky phenolics from naturally occurring Lactobacillus if they are making a BJCP English Cider (some seem to use Brett but that’s another conversation).

These aromas/flavors are the result of the LAB breaking down phenolic acids in the apple juice. Again, these phenolics are not associated with the Oenococcus oeni strains that winemakers are pitching to finish their product, so do not make the mistake of grabbing such a vial and expecting it to suddenly “turn your cider English”. To my knowledge there are still no commercially-made Lactobacillus strains made just for the production of these phenolics. It happens naturally, or we inoculate cider we want to experience MLF with cider that is already undergoing MLF. Also, don’t confuse the phenolic substances being acted upon with the true apple tannins. Dessert apples can have plenty of the phenolic acids and very low tannin levels, i.e. one does not need a tannic cider to be able to perform MLF.

Pronounced barnyard funk aroma without the spicy and smoky phenolics generally indicates a Brett infection and is a flaw.

Diacetyl Production

When Beer Judges that tell me something subtle like a Kolsch “just tastes like nothing/bland/blonde ale/water to me” – then I tend to believe they could use some more practice before becoming a Cider Judge. Judges need to be able to appreciate subtlety to judge cider, especially C1. Beer Judges like to pick on certain faults, and a great many have trained themselves to be sensitive to the buttery flavor and aroma, and slick mouthfeel of diacetyl. Few professional cidermakers I’ve met feel as negatively about it as the average Beer Judge. Presence of diacetyl is not a reason to not perform a full sensory analysis of the cider (or mead, or beer…). Please take that to heart with your judging if you are particularly sensitive to diacetyl. Remember these can be very dry, delicate beverages. A small amount of butter isn’t really a reason to disqualify a cider from medal contention, but diacetyl should never be a dominant character.

I tend to associate noticeable Diacetyl more with Oenococcus than Lactobacillus but I believe that is 1) strain dependent and 2) because of what else is going on – there are no spicy/smoky flavors to cover up that butter. Those of you who have taken a liking to (or hatred for) Chardonnay are probably familiar to the common buttery profile from MLF. If you are blind or extremely sensitive to diacetyl it is good to discuss this with your fellow judge before the flight.

Promotes Stability

“…Hey, wait! You said it increases pH, so how does it promote stability?!? You must have that backwards!” OK, that does seem counter-intuitive but remember what is going on. Malic Acid is the target of multiple microbes, thus its presence makes the cider somewhat more susceptible than a cider without malic. Also, in performing malolactic fermentation LAB are removing other nutrients from the cider or wine. Thus, those nutrients are not available for other spoilage microbes to consume. If they cannot survive, they cannot do much to spoil a cider. High pH cider is not really desirable, and all other things equal one should try to keep pH at or below 3.8, but if a cider is dry and LAB have used up the last micronutrients available, there isn’t much left for spoilage microbes to chew on even if pH is a bit higher than ideal. With appreciable residual sugar, fairly low acid, and low alcohol content, French Cider can be among the least stable cider you will encounter. Just a small amount of nutrient becoming available can sometimes reactivate such ciders in the bottle.

Mousiness

At low levels I associate mouse with an initial bready flavor that lingers in the aftertaste, building in strength on the palate, very often becoming Cheerio- or (unbuttered) popcorn-like, with a bit of an unpleasant film-like feel on the tongue. The name “mousiness” is because while low levels of it can be minimally unpleasant, higher levels, especially with a higher-pH palate, may taste like a mouse cage. I’ve heard “wet rodent fur” a few times, and that is never going to be a positive combination of adjectives for something you put in your mouth. Mouse itself has no aroma, though I do sometimes associate a certain bread-like aroma with other processes LAB are performing on cider at the same time they are creating mouse.

Mousiness is never a positive in cider and wine, and is to be avoided, while some find it quite pleasant in beer. Ability to detect mouse varies significantly, but an alkaline mouth rinse can often help make the flavor more noticeable. Some judges cannot detect mouse at all, while others do not even need the mouth rinse for the level to be extremely objectionable. Everyone’s palate is different, and you should expect even your own ability to detect it to vary with pH of your palate at a given moment.

If you’ve been making or judging sour beer or experienced wine that has gone mousy, you may be familiar with THP, aka the various Tetrahydropyridines. Some sour beer brewers seem to experience THP aging out over time, some believing it has been transformed into something with a higher detection threshold. That seems plausible, but I’ve never experienced Mousiness that went away in cider or wine. If the infection is moderate to severe and your sensitivity fairly high, it can become undrinkable. Mousiness in cider is at best incompletely understood, but we do know it is a fault. I encourage new cidermakers to avoid it with sulfite and sanitation, and not start experimenting until they know their process, have a history of creating “clean” cider, and are prepared to dump what doesn’t turn out. As Judges we point out its presence, intensity, and effect on drinkability, but don’t try to diagnose without complete information.

Other Changes

This is far from an exhaustive list of changes possible during MLF but hits most of the major ones. It may also effect clarity, change color, and have other minor flavor and aroma contributions.

Where will you encounter it?

C1B English C1C and French are by far the most common BJCP styles featuring MLF you can taste. New World Cider as BJCP defines it should be free of smoky/spicy/old horse MLF character. If a competition used the GLINTCAP New World – Heritage style I wouldn’t call a very small amount of MLF flavor/aroma a serious fault, and it would have to not clash with the higher acidity.

What about in C2 Specialty Cider and Perry? Personally I have entered a few English + extra ingredients/processes ciders, featuring MLF. I would instruct any entrants to TELL THE JUDGES WHAT TO EXPECT. Phenolics can and usually do seem out of place if not expected. If I read that the base to a fruit cider is English I’m going to expect tannin, and not be surprised by moderately high MLF. With French I expect less. As an entrant, if such a character is very light, I will indicate it on the entry form – “Bourbon barrel-aged Northern Spy + bittersweet apple blend, slight MLF.” The advice from Beer Judges rings true here too: Don’t give a judge an excuse to not fully judge your (cider).

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I’m still working a discussion of cider flaws, but that is coming up next. Confused, outraged, or eternally grateful with what I’ve written? Fellow judges may contact me.