Can we discuss malolactic fermentation?

Ever since cris n's posted the topic regarding acidity I have been wondering more about malolactic fermentation. So my questions are: How do you know which reds undergo this process. If most quality reds undergo this process, why do we not perceive butter or cream qualities on the palate, like we do with whites that undergo MLF? If one red tastes smoother does that mean it's probably undergone MLF? Is more MLF better? There have been cases with very fruity young modern Cabs or Merlots where I have tasted green apple, does that mean they only had limited MLF...and does that indicate lower quality?

I would love to hear everyone's thoughts, opinions, and facts about MLF...oh and I am wondering if Robin has an article about it...I would love to read it...LOL!

You need to leave this forum -- intelligent questions make us nervous, especially Yaniger. He is already on the verge -- do you want to be the one who pushes him over into the abyss?

This excerpt is from a Cornell University course:

Malolactic Fermentation

As you have undoubtedly learned in other sections of this course, the conversion of malic acid to lactic acid by lactic acid bacteria (LAB) in wine has a profound effect on wine. There is a reduction in acidity and rise in pH, and the wine develops a more complex aroma and mouthfeel.

Generally, the winemaker can choose whether or not to put a wine through MLF. In red wines MLF is used much more often than not, and it often occurs spontaneously. There will be more about opting not to use MLF in the section on white wines.

The timing of MLF can have a major effect on the contribution it makes to the wine's aroma and mouthfeel. Most winemakers feel that MLF occurring simultaneously with alcoholic fermentation has less of an impact than if it occurs afterwards. This can be especially important with red wines, where obvious 'buttery' character is not desirable.

Even more important is the LAB strain used. Winemakers currently have a choice of about a dozen strains, each with its own unique metabolic 'fingerprint'.

Interestingly, the vessel in which MLF occurs can influence wine aroma. Just as with wine yeast, LAB enzymes appear to react with soluble substances in oak barrels, creating a dramatically wider range of flavors in a wine than would be produced in an inert vessel. This may be one reason why French wines are often regarded as more complex than their American counterparts: traditionally MLF occurs in the spring following vintage, while the wine is in barrel.

This is an interesting subject that I'm sure is debated among winemakers ad nauseum.

If most quality reds undergo this process, why do we not perceive butter or cream qualities on the palate, like we do with whites that undergo MLF?

That struck me as a pretty interesting question, Maria, so I took a look on PubMed (a service that allows the searching of scientific journals) to see what I could find. According to an article in The International Journal of Food Microbiology (Marchand, et al., 2000 Oct;48(10):4890-5) it's been shown that the perception of butteriness in wines due to the presence of the chemical diacetyl is highly dependent on the composition of the wine. It takes a much higher level of diacetyl to give a red wine a buttery character than it does a white wine. Haven't done enough looking around to find out if anyone knows why this is, though.

Mike

Maria, there is a great book on home winemaking that you can download for free. From the WLDG Home Page, click on "Favorite Links" (left hand column), then click on "Home Winemaking" and you'll find a link to "THE HOME WINEMAKERS MANUAL" by Lum Eisenman.
Chapter 13 is titled
"MALOLACTIC AND OTHER FERMENTATIONS (link). The entire book can be downloaded and contains a great wealth of information, not just for home winemakers, but for anyone interested in the winemaking process.
Chapter 13 states: ".....Most high quality red wines are produced by two distinctly different fermentations. First, yeast converts the grape sugars into ethanol, and then bacteria in the wine convert malic acid into lactic acid. The conversion of malic acid into lactic acid by bacteria is called Malolactic (ML) fermentation, and ML fermentation produces significant changes in wine. Lactic acid is weaker than malic acid, so ML fermentation reduces wine acidity. This reduction in acidity is often used to improve the balance of wines excessively high in acid. ML fermentation removes unstable malic acid from the wine, and when all of the malic acid is gone, the wine is more biologically stable. Small quantities of different byproducts are produced during malolactic fermentation, and some of these byproducts make positive contributions to the quality and complexity of the wine....."

Maria, it's not just "most quality reds" that go through malolactic, it's almost *all* reds. The main motivation for putting a red through MLF isn't changes in taste, it's stability of the wine in the bottle. A wine with malic acid remaining "wants" to go through MLF and may choose to do so at an inopportune time, like in the bottle. In whites, the flavor changes brought on by MLF are obvious and a wine makers often choose not to allow it. Stability is still an issue, so MLF in the bottle is prevented, usually by sterile filtration and additional SO2, one reason SO2 levels are often higher in whites than in reds. In reds, the flavor changes are not so obvious (and usually positive), so the desire for stability in the bottle almost always wins. It's easier to go through MLF than it is to keep a non-MLF wine bottle-stable.

As for not detecting in reds the diacetyl that is responsible for "buttery" tastes in white, as Mike found, the treshold for detection of diacetyl has been documented to be much higher in reds than in white. Why is a question I can't answer but obviously reds taste much different than whites.

Beyond that, it is possible for a winemaker to either minimize or maximize diacetyl content in the final product. In MLF, diacetyl content peaks about the same time the malic acid disappears. If the ML bacteria is allowed to continue after that, it can actually metabolize the diacetyl and concentrations fall. Some yeasts also consume diacetyl. So, for example, a red wine maker might (and often does) start MLF immediately after primary fermentation or even before it is complete, while lots of yeast is still around. Not wishing to maximize diacetyl, he has no reason to interrupt MLF and so both yeast and ML bacteria would reduce diacetyl concentrations by the end of the process. A California chardonnay producer wishing to maximize "butteriness", on the other hand, might filter between primary fermentation and MLF - no yeast to consume MLF-produced diacetyl. He might also interrupt MLF just as malic acid disappears (and diacetyl peaks) by chilling and filtering again.

My two cents' worth on MLF!

How do you know which reds undergo this process.

It isn't necessarily something you can just tell by tasting, but these days most reds go through MLF. It depends on the style (red wines with naturally lower pH's may not - i.e., fresh, fruity, more acidic styles).

If most quality reds undergo this process, why do we not perceive butter or cream qualities on the palate, like we do with whites that undergo MLF?

As I mentioned in the cris n. initiated "acidity" thread, the buttery quality of MLFed wines isn't intrinsically due to MLF itself, it's due to the presence compounds which are an MLF byproduct (primarily diacetyl). Their production and continued presence in wine depends on a number of issues. Mike quite rightly notes above that the organoleptic perception of diacetyl is also dependent on wine type - the same concentration of the compound will be much more obvious in a Chardonnay than in a Cabernet Sauvignon.

If one red tastes smoother does that mean it's probably undergone MLF?

Not necessarily, as palate "smoothness" may be due to a number of other factors (e.g. tannins). But a wine put through MLF will generally tend to seem "softer" than if it hadn't been.

Is more MLF better?

Not necessarily. Sorry to keep repeating myself but, again, it just depends on the style. Full MLF can potentially provide reduced stability risk (assuming sterile filtration is not undertaken, as well as a number of other issues).

There have been cases with very fruity young modern Cabs or Merlots where I have tasted green apple, does that mean they only had limited MLF...and does that indicate lower quality?

Non/partial-MLF doesn't indicate lower quality. A "green apple" flavour is not associated with MLF.

(For a more technical discussion you can check out: http://www.brsquared.org/wine --> Articles --> Malolactic Fermentation.)

Hope that answers your questions sufficiently,

Ben

How do you know which reds undergo this process.

It isn't necessarily something you can just tell by tasting, but these days most reds go through MLF. It depends on the style (red wines with naturally lower pH's may not - i.e., fresh, fruity, more acidic styles).

Ben,

Which 'more acidic' red wine types don't go through ML?

Ben,

Which 'more acidic' red wine types don't go through ML?

I'm not Ben, but ML will not take place if the acid level is too high. I believe total acidity levels higher than 1.1% retard the developement of ML. Often, if levels are that high, the winemaker may reduce the level chemically so ML can take place. This can sometimes backfire. The carbonates (potassium or calcium) which are used to reduce the acidity act preferentially on Tartaric acid, not malic. Then, when the ML takes place, the total acidity can be too low and if the pH rises above 3.6 the wine becomes can become unstable and spoil.

In addressing another issue brought up here, another reason ML is started after primary fermentation is because the ML bacteria also like sugar and we want all the sugar reserved for the yeast. Another ML issue relates to off-dry wines. Sometimes offdry wines are stabilized using potassium sorbate. If ML takes place in the presence of the sorbate, the wine will be ruined, or so I've read.
I just realized I didn't answer your question. I don't know specific reds that don't go through ML, but one guess would be Port, which, when fortified, has the alcohol content raised to the point that ML can't take place. Another guess might be those 16%abv jammy zins.

Howie,

While you are correct that starting ML is related to the wine's acidity, the pH is used to govern whether ML will start or not. A pH below 3.2 tends to inhibit ML, but of course, a pH below 3.2 normally points to relative high acidity.

There have been anamolous years in the Finger Lakes, however, when pH and total acidity were going in the same direction.

Thanks Thomas, I stand corrected. Most everything I've read refers to the pH, but, I believe, one of my books does refer to TA relative to ML. I'll look it up when I get the chance.

Thanks Thomas, I stand corrected. Most everything I've read refers to the pH, but, I believe, one of my books does refer to TA relative to ML. I'll look it up when I get the chance.

Howie,

The relationship between acidity and pH is so close that it is difficult to talk about one without mentioning the other.

[Robin Garr]

oh and I am wondering if Robin has an article about it...I would love to read it...LOL!

Ahem! As a matter of fact, I have.

Bear in mind, though, that the Wine Advisor articles are usually aimed at offering quick bites of basic wine education in (I hope) accessible form, so you've had lots more technical responses here than you'll get out of my article, which only touched briefly on malo and reds.

But for the record:

Butter in your wine?

Howie,

I know that, but I was under the impression that the vast majority of red wines went through ML, and I have only ever myself dealt with one that had not (an El Dorado zin, of all things). Maybe some SE Australian low-end Shiraz, but otherwise...And the pH of reds tends to be higher, anyway.

I've been looking up ML as a result of this thread, thank you Maria,
and there are some mysteries. For example, several technical books say that diacetyl is a by-product from the fermentation of citric acid by ML bacteria, but wine contains very little citric acid, AFAIK. Certainly overt butter is much more common in the New World than in the Old, although that could also be because white Burgundy tends to be higher in tartaric and lower in malic (and therefore ML makes less of a change in the wine).

Timing of ML is very interesting, too; my producers in Italy tend to encourage ML immediately after the primary by inoculating and heating the cellar, but some French producers believe a long, slow ML is best. Wine seems so simple until you really get into it...

...Wine seems so simple until you really get into it...

How true. As simple as fermented grapes, but the possible combinations of all the process variables is almost infinite - variety, color, terrior, weather, acidity, sugar content, skin contact, yeast strains, fermentation temperature, method and length of aging, method of stabilization, method of clarification, type of bottle closure, etc. - thus giving us the wide variety that brings us all here.

I've been looking up ML as a result of this thread, thank you Maria,
and there are some mysteries. For example, several technical books say that diacetyl is a by-product from the fermentation of citric acid by ML bacteria, but wine contains very little citric acid, AFAIK. Certainly overt butter is much more common in the New World than in the Old, although that could also be because white Burgundy tends to be higher in tartaric and lower in malic (and therefore ML makes less of a change in the wine).

Timing of ML is very interesting, too; my producers in Italy tend to encourage ML immediately after the primary by inoculating and heating the cellar, but some French producers believe a long, slow ML is best. Wine seems so simple until you really get into it...

Oliver,

It doesn't take much citric acid, apparently. Also, there are arguments, and scientific at that, over the benefits of inoculation as opposed to allowing spontaneous ML. Plus, ML is also implicated in the level of brett possible in wine, which leads to biogenic amine production, which can lead to allergic or toxic reactions. Lovely subject...

Thank you thank you all...as usual, I am learning a tremendous deal from everyone and I really appreciate all the research as well!

Ok, I guess I am going to get a little philosophical here...I wonder how much the cream/butter distinction in many white wines, and not red, is due to appearence? Just like most taste dark fruits/flowers and spices in red wine and vice versa in white. How come we don't taste butter in red or cherries in white? Do you think it's the colour of the wine that is deceiving us...ie, Chardonnay sometimes looks like melted butter so that is what we taste?

More scientifically, I guess that higher acid whites taste less buttery because the acid that was not converted by MLF could mask the diacetyl. Then how about red...maybe the tannins are also masking the diacetyl in the same way. Haven't been able to prove any of this of course...just thinking outloud...LOL!

Edited because I can't spell...LOL!!

yeah, enjoying the subject too as I keep an eye on the Iditarod. Wish I was there!
Think Jamie Goode`s book might have some MF reading, will check.

...More scientifically, I guess that higher acid whites taste less buttery because the acid that was not converted by MLF could mask the diactyl. Then how about red...maybe the tannins are also masking the diactyl in the same way. Haven't been able to prove any of this of course...just thinking outloud...LOL!

I think Mark addressed this issue pretty good above, in that the diactyl levels in red wines can drop off after ML is complete. I don't think our eyes are fooling us. I think almost anyone here could distinguish a red from a white with a blindfold on. Much of the red wine flavors (spices, cherries, plums, etc.) are extracted from the skins and seeds, along with the tannins. The wine is exposed to the skins and seeds during fermentation and the alcohol content goes up. Many of these organic compounds are soluble in alcohol and would not go into solution if the alcohol were not present. On a different track, and returning to Oliver's question, some of these organic compounds can be extracted if the must (crushed red grapes) is heated and then pressed. I believe winemakers who use this "Hot Press" method could easily make red wines that will not go through ML as the heat can kill the responsible bacteria.

Beyond that, it is possible for a winemaker to either minimize or maximize diacetyl content in the final product. In MLF, diacetyl content peaks about the same time the malic acid disappears. If the ML bacteria is allowed to continue after that, it can actually metabolize the diacetyl and concentrations fall.

I apologize Mark and Howie. I took the above statement as something that could happen but doesn't always happen.

It takes a much higher level of diacetyl to give a red wine a buttery character than it does a white wine.

Howie, I guess the above statement, researched by Mike, is also confusing me...why would this be? Any thoughts?

btw...thanks for the winemaking guide...I can't believe I can download the whole thing for free! What a great source of info!

It takes a much higher level of diacetyl to give a red wine a buttery character than it does a white wine.

Howie, I guess the above statement, researched by Mike, is also confusing me...why would this be? Any thoughts?

btw...thanks for the winemaking guide...I can't believe I can download the whole thing for free! What a great source of info!

Maria, I'm not Howie but I think the answer here is not a technical one but a sensory one that's not going to have a straightforward answer. Similar studies have been done with wine and residual sugar: under double blind conditions and with experienced tasters, the threshold for dectection of residual sugar is about 0.5%. Why 0.5%, not 0 or 1.0%? Who knows?

A similar thing is going on here, I think. Chardonnay, Pinot Noir and Cabernet Sauvignon obviously have very different flavor profiles. It seems resaonable that the threshold for detection of diacetyl is going to vary between wine varietals, just as diacetyl (or another flavor) might be easier to detect as a "buttery" in, say, your movie popcorn, than it would be in your favorite spicy Thai dish.

I realize this may not be a very satisfactory answer but I'm afraid this is a question without a nice, crisp, quantitative explanation. The studies Mike found online have shown that diacetyl is easier - much easier - to detect in some wines than in others. It just *is* and my guess is the other, competing flavors in the wine are responsible.

Thanks Mark! ITA. It's amazing how complex wine really is...not just the taste, but the whole winemaking process. Absolutely fascinating. Do you make wine?

Thanks Mark! ITA. It's amazing how complex wine really is...not just the taste, but the whole winemaking process. Absolutely fascinating. Do you make wine?

I have made my own wine but am a neophyte compared to the likes of Howie. I also worked pouring wine at a winery in the Sierra Foothills (California) where my boss was also the winemaker. So I was able to ask her questions about my own winemaking. I also helped out occasionally with winerywork beyond pouring, which gave me the opportunity to ask still more questions. I learned a lot.