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Secondary Aromas — From Fermentation

Secondary aromas are the captivating compounds born from fermentation and winemaking choices, transforming grape juice into a layered, complex sensory experience.

Secondary aromas develop through the winemaking process, primarily from alcoholic fermentation by yeast (producing esters), malolactic fermentation by lactic acid bacteria (producing diacetyl and lactic compounds), and extended lees contact (producing autolytic characters). These aromas range from the banana and bubblegum of carbonic maceration wines to the butter and brioche of MLF and sur lie aging. Identifying them is a core skill in professional wine evaluation and essential for WSET and Court of Master Sommeliers tasting assessments.

Key Facts

Isoamyl acetate is the primary ester responsible for banana aromas in wine; it is formed by the condensation of acetyl-CoA and isoamyl alcohol during fermentation, and its production is influenced by fermentation temperature, yeast strain, and nutrient levels
Diacetyl (2,3-butanedione), the main buttery compound in wine, is produced chiefly by Oenococcus oeni during MLF through metabolism of citric acid; desirable concentrations are typically 1–4 mg/L, while levels above 5–7 mg/L are considered a fault
Diacetyl sensory thresholds vary significantly by wine type: as low as 0.2 mg/L in Chardonnay, 0.9 mg/L in Pinot Noir, and 2.8 mg/L in Cabernet Sauvignon, meaning winemakers must manage MLF differently by variety
Carbonic maceration, the technique used in Beaujolais Nouveau production, produces elevated levels of esters such as ethyl cinnamate, contributing characteristic strawberry, raspberry, and bubblegum aromas distinct from conventional yeast fermentation
Sur lie aging triggers yeast autolysis, where dead yeast cells decompose and release amino acids, mannoproteins, and fatty acids that contribute brioche, biscuit, and nutty secondary aromas; Champagne AOC requires a minimum of 15 months on lees for non-vintage wines
MLF conducted via co-inoculation of yeast and bacteria tends to produce lower diacetyl levels and fruitier profiles, whereas sequential inoculation (bacteria added after alcoholic fermentation) results in higher diacetyl and more pronounced buttery character
Secondary aromas are produced by fermentation and post-fermentation winemaking decisions; wines with minimal intervention such as stainless-steel-fermented, non-MLF wines may display few or no secondary aromas at all

📚Definition and Origin

Secondary aromas are volatile compounds derived from the winemaking process rather than from the grape itself. They sit between primary aromas (varietal character from the grape) and tertiary aromas (bouquet from bottle aging). According to WSET's Systematic Approach to Tasting, aroma characteristics are evaluated in terms of primary, secondary, and tertiary origin. Secondary aromas arise primarily from three sources: alcoholic fermentation by Saccharomyces cerevisiae (producing esters and higher alcohols), malolactic fermentation by lactic acid bacteria such as Oenococcus oeni (producing diacetyl and lactic compounds), and lees contact or aging in oak (releasing autolytic and wood-derived compounds).

Yeast-derived esters: isoamyl acetate (banana), ethyl butyrate (pineapple), phenethyl acetate (rose, honey)
MLF-derived compounds: diacetyl (butter, butterscotch), acetoin, ethyl lactate
Lees contact and autolysis: brioche, biscuit, toasted nuts, bread dough
Oak-derived secondaries: vanilla from vanillin, clove from eugenol, coconut from lactones

🔬How Secondary Aromas Develop

During alcoholic fermentation, Saccharomyces cerevisiae produces esters as metabolic byproducts when alcohols combine with acids and acyl-CoA molecules. Higher fermentation temperatures and stressed yeast conditions tend to increase ester production, while cooler fermentation can preserve primary varietal character at the cost of ester complexity. Malolactic fermentation, typically conducted after primary fermentation using Oenococcus oeni, converts L-malic acid to L-lactic acid and produces diacetyl as a key intermediate through citric acid metabolism. The timing of bacterial inoculation strongly influences diacetyl levels: sequential inoculation typically results in higher diacetyl than co-inoculation, which produces fruitier profiles with lower buttery character. Extended lees aging promotes autolysis, releasing amino acids and polysaccharides that contribute bready, nutty, and creamy secondary complexity.

Ester formation: acetyl-CoA combines with higher alcohols during active fermentation to create fruity esters
Diacetyl biosynthesis: produced by O. oeni through citric acid metabolism; levels depend on inoculation strategy and O. oeni strain selected
Autolysis during sur lie aging: yeast cell walls break down, releasing mannoproteins, fatty acids, and amino acids into the wine
Higher fermentation temperatures and yeast stress tend to increase ester production, which can be desirable or a fault depending on style

👃Why Secondary Aromas Matter in Tasting and Winemaking

Secondary aromas are a direct record of a winemaker's cellar decisions. The presence of prominent buttery diacetyl notes reveals that MLF has occurred and was managed to preserve, not suppress, its influence. Brioche and biscuit aromas indicate extended lees contact. Banana and bubblegum esters point to carbonic or semi-carbonic maceration, as seen in Beaujolais Nouveau, where esters including ethyl cinnamate lend strawberry, raspberry, and bubblegum character. For professional tasters, the ability to recognize and correctly attribute secondary aromas is tested in WSET Level 3 and Diploma examinations, where candidates are expected to identify fermentation and winemaking influences as part of a structured tasting note. A wine with no secondary aromas is likely minimally intervened, fermented in stainless steel with MLF suppressed.

Diacetyl presence and intensity signal whether MLF occurred and how it was managed; co-inoculation produces fruitier profiles while sequential inoculation produces more buttery wines
Brioche, biscuit, and bread-dough aromas from autolysis indicate sur lie aging, most prominently in Champagne and white Burgundy
Carbonic maceration esters (bubblegum, kirsch, strawberry) are intentionally maximized in Beaujolais Nouveau; they fade quickly, making these wines best consumed young
Wines with no detectable secondary aromas are typically stainless-steel-fermented, non-MLF styles designed to showcase primary fruit and varietal character

🍷Identifying Secondary Aromas in the Glass

To isolate secondary aromas, smell the wine immediately after pouring and again after a few minutes of air exposure, allowing volatile esters and diacetyl to volatilize into the headspace. Banana and bubblegum signals a carbonic maceration wine or an ester-heavy fermentation style; butter or butterscotch signals diacetyl from MLF; brioche, biscuit, or toasted bread points to autolysis from lees aging. Comparing a young Beaujolais Nouveau (ester-forward) against a Muscadet Sur Lie (autolytic, slightly creamy) against a barrel-fermented, full-MLF Chardonnay (diacetyl and oak combined) is the most efficient way to calibrate recognition of the three major secondary aroma families. The Aroma Wheel, developed at UC Davis, clusters these as fermentation-derived and processing-derived categories.

Butter and butterscotch aromas: diacetyl from MLF; intensity depends on bacterial strain, wine type, and inoculation timing
Brioche, biscuit, toasted nuts: autolysis from extended lees contact; most pronounced in traditional-method sparkling wines
Banana, bubblegum, strawberry, raspberry: esters from carbonic or semi-carbonic maceration and high-ester yeast fermentation
Secondary aromas tend to diminish with bottle aging, replaced by tertiary aromas such as dried fruit, leather, tobacco, and forest floor

⭐Classic Examples in the Wine World

Beaujolais Nouveau is the archetypal ester-driven wine: produced from Gamay via semi-carbonic maceration, it is released every third Thursday of November and showcases elevated esters including ethyl cinnamate, yielding characteristic strawberry, raspberry, and bubblegum aromas. Champagne is the defining example of autolytic secondary aromas, with non-vintage wines required to spend at least 15 months on lees and vintage wines a minimum of 3 years; some prestige cuvees rest for considerably longer, developing pronounced brioche, biscuit, and toasted-nut complexity. White Burgundy (Chardonnay from producers throughout the Cote de Beaune) frequently undergoes full MLF combined with batonnage on fine lees, layering diacetyl butter over lees-derived creaminess. Muscadet Sur Lie, from the Loire Valley, is labeled for its mandatory lees aging and shows a distinctive bready, slightly creamy secondary character at an accessible price point.

Beaujolais Nouveau: semi-carbonic maceration from Gamay produces strawberry, raspberry, and bubblegum esters; best consumed within the first year
Champagne: minimum 15 months lees contact for non-vintage, 3 years for vintage; autolysis delivers brioche, biscuit, and toasted-nut complexity
White Burgundy Chardonnay: full MLF with batonnage produces diacetyl butter layered over lees-derived richness and creamy texture
Muscadet Sur Lie: Loire Valley Melon de Bourgogne aged on lees before bottling, producing bread-dough and light creamy secondary notes

🔗How Secondary Aromas Fit the Broader Aroma Framework

Wine professionals and students classify aromas into three groups. Primary aromas originate in the grape variety itself, shaped by climate and viticulture, and include fruit, floral, and herbaceous notes. Secondary aromas arise from fermentation and post-fermentation winemaking decisions, including yeast selection, MLF management, oak treatment, and lees aging. Tertiary aromas (collectively called the bouquet) develop through bottle aging, where wines capable of aging will gradually lose primary fruit character and develop complex oxidative and reductive compounds: dried fruit, leather, tobacco, mushroom, and forest floor in reds; nutty, honeyed, and petrol notes in aged whites. The WSET Systematic Approach to Tasting explicitly asks students to identify whether aromas are primary, secondary, or tertiary in origin, and to assess the wine's developmental stage accordingly.

Primary aromas: varietal and terroir character from the grape (blackcurrant in Cabernet Sauvignon, lychee and rose in Gewurztraminer)
Secondary aromas: from winemaking choices including MLF, yeast strain, fermentation temperature, oak, and lees contact
Tertiary aromas (bouquet): emerge with bottle age through oxidative and reductive reactions; dried fruit, leather, tobacco, mushroom in reds; honey, petrol, nuts in whites
Wines with no secondary aromas are typically minimally intervened styles designed to foreground primary varietal character