Malolactic Fermentation

By Bill Collings

What Is It?

Malolactic fermentation is “the conversion by bacteria of malic acid into CO2 and lactic acid.” Approximately one gram of malic acid transforms into roughly 0.67 grams of lactic acid and 0.33 grams of CO2.

Why Use It?

Several compelling reasons exist for employing this process:

The primary motivation involves reducing acidity in red wines and select white varieties through organic rather than chemical means. Since spontaneous malolactic fermentation frequently occurs after bottling—particularly when spring temperatures rise—controlled induction prevents unpredictable quality changes.

The process produces stylistic improvements: wines lose their “hard and acidic edge,” developing richer grape aromatics and fuller body. Additionally, “the more aggressive and pronounced malic acid is replaced by the less aggressive lactic acid,” creating smoother wines with potential buttery notes from diacetyl formation.

Not Recommended for All Wines

Aromatic varieties like Gewurztraminer and Riesling should avoid this fermentation since “they depend upon the malic acid to enhance their flavour components.”

Critical Conditions

Success requires:

• pH around 4.0 for starters; above 3.3 for reds, 3.4 for whites
• Temperatures between 20–30°C
• Low alcohol levels
• Low SO2 levels (10–20 ppm)
• Unclarified wine containing adequate nutrients

Available Cultures

Three main options exist: freeze-dried cultures, liquid cultures from Oregon State University, and dried Oenos Viniflora cultures, each offering different advantages regarding cost, temperature tolerance, and ease of use.