EXPLAINED Malolactic fermentation
Put simply, malolactic fermentation (or MLF) is the conversion of malic acid into lactic acid within a grape must or wine. It’s a common – in some styles necessary – step which takes place in the winery and is facilitated by lactic bacteria.
The process ‘softens’ the acidity through the conversion of harsh-tasting malic acid into softer lactic acid, and also raises the pH of the wine. The bacteria can be introduced to the wine via inoculation during or after alcoholic fermentation, but the bacteria is present in many cellars, so spontaneous MLF can occur.
The process (technically a bacterial conversion rather than a fermentation, because it doesn’t use yeast) also helps to stabilise the wine by preventing it from going through spontaneous MLF later, potentially after bottling.
DOES IT BENEFIT ALL WINES?
No, not at all. MLF is generally undesirable in some styles, particularly aromatic and zingy, high-acid whites such as Riesling and Sauvignon Blanc. Winemakers can inhibit malolactic fermentation by adding sulphur dioxide post-fermentation or through the use of enzymes.
Red wines more commonly benefit from MLF than whites, where high acidity is a key character of the wine. Exceptions include Chardonnay and Viognier, which routinely go through ‘malo’ for a softer, more rounded acidity.
There are no hard and fast rules, though. In Bordeaux in 2014, for example, châteaux used MLF to control high acidity in white wines made from Semillon and Sauvignon Blanc.
The late Professor Denis Dubourdieu, one of Bordeaux’s most respected winemakers and the 2016 Decanter Hall of Fame Award recipient, noted in his summary of the 2014 vintage that partial malolactic fermentation ‘rarely practised on white Bordeaux... was recommended for the most acidic lots. When well done, this made the wines rounder without detracting from their typicity’.
While most reds undergo malolactic fermentation to help accentuate fruity and berry characters and remove some of the harsh acid notes, reds that have been grown in very warm climates and lack natural acidity do not benefit from the process because it makes them less balanced and more unstable.
Many red wines undergo malolactic fermentation in barrels. As well as taming brisk acidity and enhancing fruit notes, this can promote a wine’s smoky and spicy notes, too.
Wines aged in oak typically undergo MLF, so this is one way of deciphering whether a wine has gone through malo or not; other clues include a creamy, oily texture, a rounder acid profile and a higher pH – if you have access to the technical data.
Rathfinny, Blanc de Blancs, Sussex, England 2017
£38.99 Carruthers & Kent, Harrods, Harvey Nichols, Hedonism, Lea & Sandeman, Rathfinny, The Fine Wine Co, The Oxford Wine Co, Waud Wines
This is the second release of the blanc de blancs, made from eight different clones of Chardonnay, vinified separately. From chalky soils, the grapes were picked late at the end of October. The ripeness of the fruit meant no chaptalisation was necessary, but the wine did go through malolactic to round it out and add lactic notes. There’s a weight of ripe fruit on the nose and palate, almost tropical in character. Fresh acidity and a lick of salinity. 2021-2025 12%
Drink Alc Wairau Cove, Chardonnay, Gisborne, New Zealand 2020
£7 Tesco The nose is sweetly floral and full of tropical fruit, as well as a butterscotch, honeyed character. The high acidity wraps up the plump fruit, honey and buttered popcorn nicely. It’s had oak ageing, lees ageing and partial malolactic, which all lend complexity and create its full, creamy mouthfeel. 2021-2022 13%
Drink Alc Fossacolle, Rosso di Montalcino, Tuscany, Italy 2019
£20.95-£25.99 Exel, Hedonism, Philglas & Swiggot, The Fine Wine Co, The Wine Reserve
From 4ha in the village of Tavernelle, south of Montalcino. This village is known to produce perfumed wines with ripe tannins and great depth. After the maceration and both alcoholic and malolactic fermentations, the wine ages for a year in second-fill oak. Over cassis, macerated roses and cherry gush smoky woodland notes. The tannins are firm and grainy, and the acidity super-integrated. 2021-2027
Drink Alc
14%