Malolactic Fermentation: Why Wine Is Buttery or Fresh

Time to explain a perhaps complex wine term as simply as possible. I'm talking about the process that determines whether your glass is creamy and round or sparklingly fresh: malolactic fermentation.

Malolactic fermentation is a much-discussed step in winemaking. For many, this secondary fermentation can be confusing: is it a fermentation? Does every wine have to undergo it? In this blog post, I'll explain in plain language what malolactic fermentation is, what it does to wine, and when winemakers prefer or deny it.

What is malolactic fermentation?

Malolactic fermentation isn't a classic yeast-based fermentation, but a microbiological process in which lactic acid bacteria convert malic acid (a tart acid commonly found in grapes) into lactic acid. It's actually a fermentation, not a yeast-fermentation. Malic acid is quite acidic and gives wines their fresh, crisp acidity; lactic acid is milder and softer. This softens the flavor and changes the wine's texture.

In short:

Malolactic fermentation = It is the conversion of malic acid to lactic acid by bacteria.

What does it do to wine?

• Acid reduction : The wine becomes less tart because malic acid (with a higher acidity) changes to lactic acid (milder). This rounds out the flavor. This is more noticeable in white wine; red wine contains so little malic acid that it's barely noticeable.
  
• Texture : Wines feel fuller and creamier after malolactic fermentation.
  
• Aromas : Malolactic fermentation can produce developed aromas such as buttery (due to diacetyl ), nutty, and creamy notes. Diacetyl is a byproduct that often gives Chardonnay its buttery profile.
  
• Stability : Malolactic fermentation is almost standard for red wines; it stabilizes the wine microbiologically and makes it less susceptible to unwanted subsequent fermentation in the bottle. This doesn't happen with Beaujolais Nouveau, where fermentation is halted by a different process ( carbonic maceration ) , but that's a story for later.
  

Is it a second fermentation?

Sometimes "malo" is also called "second fermentation." It's not caused by yeast, which can be a bit confusing. It produces (almost) no CO2 like alcoholic fermentation by yeast. It's a bacterial conversion, so technically not a classic fermentation, but in practice, it often follows alcoholic fermentation and is therefore called "second fermentation." Sometimes, some carbon dioxide is released, and you can sometimes notice this as a slight fizz in a Riesling. This is often a result of this process.

Malolactic wine: which wines undergo it?

• Chardonnay: Many (but not all) Chardonnays undergo malolactic fermentation to achieve that buttery, creamy flavor. Winemakers can choose how much diacetyl they want to use.
  
• Red wines: Malo is common in many red wines (e.g. Cabernet Sauvignon, Merlot) because it balances tannins and acidity and creates a smooth mouthfeel.
  
• Wine styles that need to remain fresh (e.g. many Sauvignon Blancs or light, crisp Chardonnay styles) avoid retaining malic acid and crisp acidity.
  

How do winemakers initiate/control the malolactic process?

• Temperature and pH: Winemakers regulate temperature and pH to promote or inhibit MLF (another term for malolactic fermentation).
  
• Inoculation : adding selected lactic acid bacteria to obtain controlled malolactic fermentation.
  
• SO2 and filtration: Sulphur dioxide (SO2) and filtration can prevent MLF if a wine needs to stay fresh.
  
• Wood aging: Malo can be aged in oak barrels; contact with wood can influence the development of buttery notes. It can also be aged without wood contact.
  

Practical tips for you

• Want buttery? Choose a Chardonnay you know has been aged in oak and made with malolactic fermentation. Because the two are often linked, oak aging is easier to track down.
  
• Looking for a fresh wine? Look for terms like "no malo," "malolactic inhibited," or choose fresh regional and grape styles (e.g., "unoaked" Chardonnay or Sauvignon Blanc).
  
• Label check: Wine labels rarely state it explicitly, but wine descriptions and producer websites sometimes indicate whether the wine has undergone malolactic fermentation.