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. 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; 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. Diacetyl is one of the major compounds O. oeni produces during MLF, contributing buttery or butterscotch aroma and flavour, and it is formed through the metabolism of citric acid. 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
• Diacetyl: formed by O. oeni through citric acid metabolism during MLF
• Under reductive conditions diacetyl can be reduced to acetoin and then to 2,3-butanediol, which can have little to no sensory impact
• Winemaking factors shift diacetyl: longer MLF gives higher concentrations, high O. oeni numbers give lower, and long yeast lees contact gives lower

MLF is conducted in virtually all red wines, numerous white wines and sparkling wine bases, and the choice of bacterial strain and timing of inoculation 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). 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, the recommended approach is a sequential MLF with a high diacetyl-producing strain. 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
• In 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
• Tank method sparkling wines spend little or no time on lees, keeping the focus on primary fruit and aromatic freshness

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. The lees in the bottle are yeasts that die and decompose by the end of the second fermentation, a process known as autolysis. All Champagnes must spend at least 15 months maturing in the winemaker's cellars before release, and vintage cuvées are matured for at least three years; 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 presents 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 Burgundy, white wines are left to undergo malolactic fermentation, and wines aged on lees in 228-litre casks get batonnage, regular stirring with a stick to suspend the lees again. The typical Californian Chardonnay is 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
• Muscadet: several months on lees, with aromas from citrus fruit to brioche notes
• White Burgundy: malolactic fermentation, and optional lees ageing with batonnage in 228-litre casks
• California Chardonnay: MLF, lees contact and oak give a toasty, buttery style

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. Among fermentation-derived esters, isoamyl acetate is linked with banana, ethyl hexanoate with apple peel, fruit and pineapple, and phenylethyl acetate with rose and honey. These esters decrease rapidly in the first year in bottle. In Decanter in 2015, Benjamin Lewin MW wrote that yeast strain 71B was 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 calls semi-carbonic maceration a term specific to the region: whole bunches begin intracellular fermentation, and for the primeur wines, Beaujolais Nouveau and Beaujolais Villages Nouveau, the process takes 4 to 6 days. Beaujolais Nouveaux are released on the third Thursday of November. Carbonic maceration is associated with strawberry/raspberry and cherry/kirsch aromas, particularly in Beaujolais, and Decanter lists bubble gum, kirsch, banana and strawberry among its key flavours.

• Fermentation-derived esters: isoamyl acetate, banana; phenylethyl acetate, rose and honey
• WSET Level 3 files banana and pear drop under primary aromas (grape and alcoholic fermentation)
• Decanter (2018) links esters such as ethyl cinnamate, produced in higher than normal quantities in carbonic processes, to raspberry, strawberry and bubblegum flavours
• Beaujolais Nouveau: released on the third Thursday of November

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. The Comité Champagne frames maturation on lees as combining yeast autolysis and slow oxidation, gracing the wine with so-called tertiary aromas of maturity and fullness, while WSET's sparkling wine guide has long-aged vintage sparkling wines developing 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)
• The Comité Champagne 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 2026-10-05