Malic Acid is converted into Lactic Acid
Malolactic Fermentation (MLF) is a prosess where tart-tasting malic acid in wine is converted into soft-tasting lactic acid. Malolactic Conversion (MLC) is another name for the same prosess.
In alcoholic fermentation, yeasts convert juice into alcohol.
In MLF, bacteria convert malic acid into lactic acid.
MLF takes place after the alcoholic fermentation (can be done at the same time), and is started by adding LAB (Lactic Acid Bacteria) to the wine.
MLF is used for most red wines and most champagne wines. It is also common for white wines that are to be oaked and stored (typically for Chardonnay).
Malolactic wines are more stable and can be stored longer. Non-malolactic wines are often to be consumed younger.
MLF adds body and new aromas to the wine. The byproduct Diacetyl adds nutty, toasted, and buttered popcorn flavors. The byproduct Acetic acid adds vinegar flavors. The wine feels softer.
Lactic acid is less acidic than malic acid. MLF reduces the flavors of malic acid (dry green apple).
Almost all red wines are malolactic fermented.
In red wines MLF converts red fruit and berry tones into chocolate, spices, and smoke.
Around 20 % of white wines are malolactic fermented.
In white wines MLF converts citrus and herb tones into butter, hazelnut, bread and toast.
This often notable in Bourgund where Chablis and Chardonnay, made from the same grapes, taste very differently.
Almost all Champagne is Malolactic.
MLF is more used in cold climate regions.
Cold climate produces more acidic wines and tend to benefit from MLF.