Why might a winemaker stop MLF or control its completion? What are the implications for aroma and acidity?

• A. Lactic acidity
• B. Acetic acidity
• C. Tartaric acidity
• D. Malic acidity

Answer: (D)

The change you’re managing with stopping or controlling malolactic fermentation is the level of malic acidity in the wine. Malolactic fermentation converts malic acid into lactic acid, which lowers the sharp, crisp edge of the wine and can add softer, creamy notes via the aroma compounds produced during the process. If you halt the fermentation early, you preserve malic acidity, giving a cleaner, more refreshing, green-apple-like character and reducing the chance of buttery aromas that come from diacetyl formation. If you let it complete, malic acidity decreases as it’s transformed into lactic acidity, the wine softens in mouthfeel, and you may also develop buttery aromas from diacetyl and related compounds.

So the key concept is that malic acidity is what MLF is changing, and stopping MLF or controlling its completion directly shapes how much of that malic acid remains, along with the accompanying aroma profile. Lactic acidity rises as MLF proceeds, but that isn’t what you’re preserving or controlling to define freshness or aroma; tartaric acidity and acetic acidity are not the primary targets of this decision in this context.