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What is Malolactic Fermentation?

Malolactic fermentation is a term you might have come across before, often referred to as ‘Malo’ or  M.L.F. – most likely in connection with Chardonnay. But what the hell is it, what does it mean in your glass, and where are you most likely to come across it?

What the hell is it?

Malolactic fermentation is a process that can happen during wine making, usually after the main alcoholic fermentation has taken place. What happens is (harmless) lactic-acid bacteria gets into the wine and converts tart, sour malic acid (also found in high levels in Granny Smith apples and even higher levels in rhubarb) into the much softer tasting lactic acid (also found in milk and other dairy products). Pretty much every red wine undergoes this process to some extent but it only happens in some whites. As a result its only really talked about with whites as its almost always a given with reds.

It can happen spontaneously in wine, completely on its own, under certain conditions. Such as if;

  • there is lactic acid bacteria ambiently in the winery that gets into the barrels or other vessels wine is stored in
  • the winery is warm enough (roughly between 20-37°c)
  • no sulphur dioxide (SO2) is added as this kills the lactic acid bacteria.

These days modern wine makers can also make it happen by;

  • adding the lactic acid bacteria directly themselves
  • having fancy temperature and humidity controlled rooms where they can keep the temperate in range of 20-37°c in which M.L.F. tends to happen effectively

Or of course stop it from happening by;

  • adding sulphur dioxide after the main alcoholic fermentation has taken place to kill lactic acid bacteria
  • keeping the temperature below 15°c where M.L.F. struggles to get going
  • filtering out of the lactic bacteria

That’s all very interesting but what does it mean in my glass of wine!?

  • Added Texture

As you would expect from Malic green apple acid being converted into soft milk acid, M.L.F makes wine feel softer, fuller, and less acidic in the mouth. With whites it gives the feeling of oiliness in the middle of the tongue.

  • Added Aromas and Flavours

As a happy by-product M.L.F., as well as the acidic conversion it creates aroma and flavour compounds.

In whites it can create flavours of nuts, baked bread, and butter (caused by a specific compound called diacetyl). These flavours go excellently with common oak flavours of nuts again, oat-mealiness, and toast and the increase in body that oak aging brings. It is common for wine stored in barrel to undergo M.L.F. as it is a) more likely to happen and b) works so well together! Many winemakers say the integration of oak and fruit flavour is even better if the wine undergoes M.L.F. in barrel. In reds higher levels can increase flavours of spice, smoke, and chocolate notes.

That all sounds great! Why doesn’t every winemaker use M.L.F. for every wine?

Whilst a creamy soft body and the flavours it can bring can greatly increase a wines mouth feel, deliciousness and complexity, wine is all about balance. M.L.F. can greatly reduce pure fruit aromas and flavours; making the wine lack fruit and freshness. Also if the wine doesn’t have enough malic or other acid left in it the pure creamy lactic acid can make a wine seem dull and flabby.

Winemakers can get the best of both worlds by halting M.L.F. after some deliciousness and creaminess has developed but before too much fruit or acid is lost. Another way is to only make some barrels undergo full M.L.F. and some not, then to blend the two. Clever wine makers!

barrel sample

Why is it M.L.F. is so often talked about with Chardonnay?

Chardonnay has such an intimate and oft talked about relationship with M.L.F. because, as a naturally high acid grape with relatively subtle flavours, it can benefit hugely from its softening and flavour giving. Many of the finest examples of Chardonnay from Burgundy (France), Mornington Peninsula, Yarra Valley, and the rest of the world, undergo partial or full M.L.F. for exactly that reason. So next time you are enjoying a delicious textural generous Chardonnay, remember to thank Malolactic Fermentation!

Itching to know more about the winemaking process? Check out our post on New Oak vs Old Oak or learn how winemakers know what the alcohol content of wine will be. 

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Matt Shaw

Matt Shaw

Matt has been obsessed with food and drink for as he can remember. Falling in love with wine was a matter of when not if. Now a WSET Diploma student and C.M.S Certified Sommelier he plies his trade at MoVida in the C.B.D.. The only time Matt is happier than when he is chatting about wine is when he has a glass of Barolo in hand and some cured meat to pick at.
Matt Shaw

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