Secondary Aromas: Lees, Malolactic and Oak

The WSET Level 3 Systematic Approach to Tasting Wine asks tasters to describe aroma and flavour characteristics as primary, secondary or tertiary. Its Wine-Lexicon (Issue 2, 2022) defines primary aromas and flavours as those of the grape and alcoholic fermentation, secondary aromas and flavours as those of post-fermentation winemaking, and tertiary aromas and flavours as those of maturation. Secondary characters therefore fall into three clusters, and the lexicon's key question for this category asks whether the flavours come from yeast, malolactic conversion or oak. The WSET Level 2 lexicon (Issue 2.1, 2026) uses the same three clusters and names lees, autolysis and flor under yeast.

• Yeast (lees, autolysis): biscuit, bread, toast, pastry, brioche, bread dough, cheese (WSET Level 3)
• Malolactic conversion: butter, cheese, cream (WSET Level 3)
• Oak: vanilla, cloves, nutmeg, coconut, butterscotch, toast, cedar, charred wood, smoke, chocolate, coffee, resinous (WSET Level 3)
• The WSET Level 2 lexicon (2026) adds yogurt to the yeast cluster and names flor alongside lees and autolysis

Lees are the yeast cells that die and settle once fermentation finishes. WSET explains that in traditional method sparkling wine these lees break down over time in a process known as autolysis, releasing aromas such as brioche, toast, pastry and cream, and that the longer the wine stays on its lees, the more intense and complex these flavours become. Malolactic fermentation (MLF) is carried out mainly by the lactic acid bacterium Oenococcus oeni, which converts L-malic acid to L-lactic acid. The AWRI names diacetyl as one of the major compounds O. oeni produces during MLF, contributing buttery or butterscotch aroma and flavour, formed through the metabolism of citric acid. Oregon State University Extension (EM 9641, 2019) adds that the amount produced depends on the O. oeni strain, fermentation conditions (pH, oxidative-reductive potential, temperature) and citric acid concentration. Oak adds a third cluster: the WSET Level 3 lexicon lists vanilla, cloves, nutmeg, coconut, butterscotch, toast, cedar, charred wood, smoke, chocolate, coffee and resinous notes.

• Autolysis: as lees break down, aromas such as brioche, toast, pastry and cream are released (WSET)
• Diacetyl: formed by O. oeni through citric acid metabolism during MLF (AWRI)
• Under reductive conditions diacetyl can be reduced to acetoin and then to 2,3-butanediol, which can have little to no sensory impact (OSU Extension)
• The AWRI lists winemaking factors that shift diacetyl: longer MLF gives higher concentrations, high O. oeni numbers give lower, and long yeast lees contact gives lower

The AWRI's 2020 MLF fact sheet describes MLF as conducted in virtually all red wines, numerous white wines and sparkling wine bases, and names choice of bacterial strain and timing of inoculation as variables that can modulate buttery and fruity characters. Inoculation most commonly follows alcoholic fermentation (sequential inoculation), but bacteria can also be added with the yeast (co-inoculation). Oregon State University Extension explains that fermenting yeast create a very reductive environment, so diacetyl produced during a simultaneous fermentation is quickly reduced, leaving low diacetyl in the wine; for buttery aromas it advises a sequential MLF with a high diacetyl-producing strain. WSET notes that some Chardonnay styles combine extensive oak contact, malolactic fermentation and lees contact to create a toasty, buttery, creamy wine, while other winemakers block malolactic fermentation and use stainless steel instead of oak for a purer expression of the variety's character.

• Co-inoculated MLF would be expected to give lower buttery character, as yeast can metabolise diacetyl to acetoin and 2,3-butanediol (AWRI)
• In AWRI-cited trials, co-inoculated Shiraz and Cabernet Sauvignon reds were rated more fruity, and research in Malbec, Chardonnay and Riesling found co-inoculated MLF gave fruitier wines than sequential MLF
• Butteriness can be masked by strong oak or very fruity characters (AWRI)
• Tank method sparkling wines spend little or no time on lees, keeping the focus on primary fruit and aromatic freshness (WSET)

The WSET Level 3 lexicon frames the question for this category directly: are the flavours from yeast, malolactic conversion or oak? Bread, biscuit, brioche, pastry and bread-dough notes point to yeast lees and autolysis. Butter, cream and some cheesy notes point to malolactic conversion. Vanilla, cloves, coconut, cedar, smoke and toast point to oak. Toast appears in both the yeast and oak clusters, and cheese in both the yeast and malolactic clusters. WSET's 2024 advice for its Level 3 tasting exam is to include primary, secondary and tertiary aromas where relevant, and to use specific descriptors.

• Butter, cheese, cream: malolactic conversion (WSET Level 3)
• Biscuit, bread, toast, pastry, brioche, bread dough, cheese: yeast, lees, autolysis (WSET Level 3)
• Vanilla, cloves, nutmeg, coconut, butterscotch, toast, cedar, smoke: oak (WSET Level 3)
• Banana and pear drop are primary descriptors in the WSET Level 3 lexicon, not secondary ones

Champagne matures on its lees in bottle. Champagne.fr explains that the lees in the bottle are yeasts that die and decompose by the end of the second fermentation, a process known as autolysis. As of 2026, the site states that all Champagnes must spend at least 15 months maturing in the winemaker's cellars before release, that vintage cuvées are matured for at least three years, and that in practice the time is nearly always longer: 2 to 3 years for non-vintage wines and 4 to 10 years for vintage Champagne. For still wine, InterLoire's Vins de Loire site describes ageing on lees as a technique specific to the Nantes vineyards, particularly Muscadet: the wine rests for several months on its lees, gaining greater roundness, a slightly pearly texture and complex aromas ranging from citrus fruit to brioche notes. In white Burgundy, the Bourgogne wines site (bourgogne-wines.com) states that white wines in the Bourgogne region are left to undergo malolactic fermentation, and describes batonnage, regular stirring with a stick to suspend the lees again, for wines aged on lees in 228-litre casks. WSET describes the typical Californian Chardonnay as full-bodied, with a distinctive toasty, buttery character from malolactic fermentation, lees contact and oak.

• Champagne: at least 15 months in the cellar before release, vintage cuvées at least three years (champagne.fr)
• Muscadet: several months on lees, with aromas from citrus fruit to brioche notes (Vins de Loire)
• White Burgundy: malolactic fermentation, and optional lees ageing with batonnage in 228-litre casks (bourgogne-wines.com)
• California Chardonnay: MLF, lees contact and oak give a toasty, buttery style (WSET)

The WSET lexicons place the aromas of alcoholic fermentation in the primary category, defined as the aromas and flavours of the grape and alcoholic fermentation; the Level 3 list includes banana and pear drop. The AWRI's table of fermentation-derived esters links isoamyl acetate with banana, ethyl hexanoate with apple peel, fruit and pineapple, and phenylethyl acetate with rose and honey. The same AWRI material notes that these esters decrease rapidly in the first year in bottle. Benjamin Lewin MW, writing for Decanter in 2015, describes yeast strain 71B, selected for nouveau wines because it increases fermentation esters, including isoamyl acetate, which gives a strong impression of bananas. Carbonic and semi-carbonic maceration add their own fruit character. Inter Beaujolais describes semi-carbonic maceration as a term specific to the region, in which whole bunches begin intracellular fermentation, and says the process takes 4 to 6 days for the primeur wines, Beaujolais Nouveau and Beaujolais Villages Nouveau. Beaujolais Nouveaux are released on the third Thursday of November. The AWRI describes carbonic maceration aromas as strawberry/raspberry and cherry/kirsch, particularly in Beaujolais, and Decanter lists bubble gum, kirsch, banana and strawberry among its key flavours.

• Isoamyl acetate: banana; phenylethyl acetate: rose, honey (AWRI fermentation-derived esters)
• WSET Level 3 files banana and pear drop under primary aromas (grape and alcoholic fermentation)
• Decanter (updated 2018), citing its tasting notes guide, says esters such as ethyl cinnamate are produced in higher than normal quantities in carbonic processes, lending raspberry, strawberry and bubblegum flavours
• Beaujolais Nouveau: released on the third Thursday of November (Inter Beaujolais, WSET)

In the WSET Level 3 lexicon, primary aromas and flavours come from the grape and alcoholic fermentation and include floral, fruit, herbaceous, herbal and spice clusters. Secondary aromas and flavours come from post-fermentation winemaking. Tertiary aromas and flavours come from maturation, in clusters for deliberate oxidation, fruit development and bottle age, with descriptors such as leather, forest floor, earth, mushroom and tobacco for bottle-aged reds, and petrol, kerosene, honey and nutty notes for bottle-aged whites. Champagne.fr describes maturation on lees as combining yeast autolysis and slow oxidation, gracing the wine with so-called tertiary aromas of maturity and fullness, and WSET's own sparkling wine guide says long-aged vintage sparkling wines develop secondary and tertiary aromas such as brioche, nuts and savoury complexity. For WSET exam notes, the lexicon places lees and autolysis descriptors under secondary.

• Primary: the grape and alcoholic fermentation (WSET Level 3)
• Secondary: post-fermentation winemaking; yeast, malolactic conversion, oak (WSET Level 3)
• Tertiary: maturation; deliberate oxidation, fruit development, bottle age (WSET Level 3)
• Champagne.fr calls the aromas of long lees maturation tertiary; the WSET lexicon lists lees and autolysis descriptors as secondary

Primary sources: https://www.wsetglobal.com/media/11766/wset_l3wines_sat_en_may2022_issue2.pdf, https://www.wsetglobal.com/media/19131/wset_l2wines_sat_en_aug2026_issue21.pdf, https://www.wsetglobal.com/knowledge-centre/blog/2026/a-guide-to-sparkling-wine-production-methods-and-regional-styles, https://www.wsetglobal.com/knowledge-centre/blog/2022/may/24/behind-the-grape-chardonnay-in-the-us, https://www.wsetglobal.com/knowledge-centre/blog/2024/what-is-beaujolais-nouveau-a-wine-tradition-making-a-comeback, https://www.awri.com.au/wp-content/uploads/mlf_modulation_AWRI_fact_sheet.pdf, https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-carbonic-maceration/, https://www.awri.com.au/wp-content/uploads/2013/08/francis-W07-AWITC15.pdf, https://extension.oregonstate.edu/catalog/em-9641-simultaneous-malolactic-fermentation-it-right-option-your-wine, https://www.champagne.fr/en/about-champagne/how-champagne-is-made/maturation, https://www.vinsdeloire.fr/en/loire-valley-wine-styles/dry-white-wine-fresh-elegant, https://www.beaujolais.com/en/2020/09/22/beaujolais-vinification-a-process-like-no-other/, https://www.bourgogne-wines.com/wine-and-terroir/our-natural-assets/vinification-and-ageing/vinification-of-white-wines/vinifying-white-wines-pressing-occurs-before-fermentation,2486,9271.html, https://www.beaujolais.com/en/a-world-for-every-beaujolais/nouveau-by-beaujolais/, https://www.wsetglobal.com/knowledge-centre/blog/2024/how-to-ace-the-wset-level-3-award-in-wines-tasting-exam. Secondary sources: https://www.decanter.com/features/yeasts-do-you-know-whats-flavouring-your-wine-245861/, https://www.decanter.com/learn/advice/carbonic-maceration-54082/. Last verified 2026-09-29