Malolactic fermentation

Malolactic conversion (also known as malolactic fermentation or MLF) is a process in <a href="/facts/Winemaking/ITBb0gpf">winemaking</a> in which <a href="/facts/Tart_(flavor)/mdB8ysuK">tart</a>-tasting <a href="/facts/Malic_acid/mSbExe77">malic acid</a>, naturally present in <a href="/facts/Grape_must/EY7texUs">grape must</a>, is converted to softer-tasting <a href="/facts/Lactic_acid/BsVRFx7s">lactic acid</a>. Malolactic fermentation is most often performed as a <a href="/facts/Secondary_fermentation_(wine)/6ektwRfF">secondary fermentation</a> shortly after the end of the primary <a href="/facts/Fermentation_(wine)/eS6uKKqQ">fermentation</a>, but can sometimes run concurrently with it. The process is standard for most red wine production and common for some white <a href="/facts/Grape_varieties/Uv1dzGHn">grape varieties</a> such as <a href="/facts/Chardonnay/xhQeDw02">Chardonnay</a>, where it can impart a "buttery" flavor from <a href="/facts/Diacetyl/lJRI6EMt">diacetyl</a>, a byproduct of the reaction.
The fermentation reaction is undertaken by the family of <a href="/facts/Lactic_acid_bacteria/qkNbMqGj">lactic acid bacteria</a> (LAB); <a href="/facts/Oenococcus_oeni/tmswMU5w">Oenococcus oeni</a>, and various species of <a href="/facts/Lactobacillus/pwoacAbe">Lactobacillus</a> and <a href="/facts/Pediococcus/BSxyw38h">Pediococcus</a>. Chemically, malolactic fermentation is a <a href="/facts/Decarboxylation/Uugc18fz">decarboxylation</a>, which means <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a> is liberated in the process.
The primary function of all these bacteria is to convert L-malic acid, one of the two major grape <a href="/facts/Acids_found_in_wine/lIF43ur4">acids found in wine</a>, to another type of acid, L+ lactic acid. This can occur naturally. However, in commercial winemaking, malolactic conversion typically is initiated by an <a href="/facts/Inoculation/M2LPGM66">inoculation</a> of desirable bacteria, usually O. oeni. This prevents undesirable bacterial strains from producing "off" flavors. Conversely, commercial winemakers actively prevent malolactic conversion when it is not desired, such as with fruity and floral white grape varieties such as <a href="/facts/Riesling/HenLwPPb">Riesling</a> and <a href="/facts/Gew%C3%BCrztraminer/9Gj4VEzp">Gewürztraminer</a>, to maintain a more tart or acidic profile in the finished wine.
Malolactic fermentation tends to create a rounder, fuller <a href="/facts/Mouthfeel/rBy2P0Sg">mouthfeel</a>. Malic acid is typically associated with the taste of green <a href="/facts/Apple/SF1WND0v">apples</a>, while lactic acid is richer and more buttery tasting. Grapes produced in cool regions tend to be high in acidity, much of which comes from the contribution of malic acid. Malolactic fermentation generally enhances the <a href="/facts/Body_(wine)/w3q6ASSm">body</a> and <a href="/facts/Flavor_(wine)/S0h7e9By">flavor</a> persistence of <a href="/facts/Wine/przCrC98">wine</a>, producing wines of greater palate softness. Many winemakers also feel that better integration of fruit and <a href="/facts/Oak_character/WvLFtNon">oak character</a> can be achieved if malolactic fermentation occurs during the time the wine is in barrel.
A wine undergoing malolactic conversion will be cloudy because of the presence of bacteria, and may have the smell of <a href="/facts/Butter/FqydR0dC">buttered</a> <a href="/facts/Popcorn/9MMa8fCz">popcorn</a>, the result of the production of diacetyl. The onset of malolactic fermentation in the bottle is usually considered a <a href="/facts/Wine_fault/XmWUxr7e">wine fault</a>, as the wine will appear to the consumer to still be fermenting (as a result of CO2 being produced). However, for early <a href="/facts/Vinho_Verde/2qaKleag">Vinho Verde</a> production, this slight <a href="/facts/Effervesce/sT0J1Vew">effervesce</a> was considered a distinguishing trait, though <a href="/facts/Portuguese_wine/7tvb8wUq">Portuguese wine</a> producers had to market the wine in <a href="/facts/Opacity_(optics)/l90q0sAV">opaque</a> bottles because of the increase in <a href="/facts/Turbidity/aqPf0q3I">turbidity</a> and sediment that the "in-bottle MLF" produced. Today, most Vinho Verde producers no longer follow this practice and instead complete malolactic fermentation prior to bottling with the slight sparkle being added by artificial <a href="/facts/Carbonation/AHnWIB8z">carbonation</a>.

Malolactic fermentation open-in-new

Malolactic fermentation