Secondary aromas in wine: what are they?

Quick answer

Secondary aromas are aromas formed or substantially shaped during fermentation and other winemaking processes.

That makes them different from primary aromas, which are mainly associated with the grape variety and its natural compounds, and tertiary aromas, which develop mainly through maturation and ageing.

Yeast can create new aroma compounds during alcoholic fermentation. Malolactic fermentation can contribute buttery or butterscotch-like notes through diacetyl. Contact with lees—the spent yeast cells and other solids left after fermentation—may bring bread, biscuit, pastry or brioche-like impressions.

These are useful associations, not diagnostic tests. A buttery smell does not prove that malolactic fermentation occurred, and a biscuit note does not prove that a wine spent time on lees. Several processes can contribute to the same aroma, while grape-derived compounds can also be changed during fermentation.

The three aroma categories

The three-part model is a practical way to organise what you smell in wine:

The boundaries can overlap. For example, a wine’s fruit character may begin with grape compounds but be altered by yeast during fermentation. A wine may also show winemaking and ageing aromas at the same time.

So “secondary” describes a likely origin or influence, not a sealed list of aromas. Wine educators and scientific sources also differ slightly in where they draw the boundary, particularly around oak and other post-fermentation practices.

For a broader introduction, see what wine aroma is. You can compare the grape-related category in primary aromas in wine and the ageing-related category in tertiary aromas in wine.

How fermentation creates aroma

During alcoholic fermentation, yeast converts grape sugar into alcohol and carbon dioxide. It also produces other compounds, including esters, higher alcohols and fatty acids, which can affect a wine’s aroma.

Some of these compounds may smell fruity or floral. That can be surprising: a fruit aroma is not automatically a primary aroma. A wine’s fruit impression may come partly from the grape and partly from fermentation-derived compounds.

The exact result depends on factors such as the yeast, fermentation conditions, nutrients, temperature and the wine itself. This is why one descriptor rarely identifies a particular yeast or production method.

You do not need to learn the chemistry to taste for this influence. When smelling a wine, notice whether its fruit and floral character feels closely tied to the grape, or whether it also has a distinctly fermentative, yeast-like or process-shaped quality. Keep that judgement tentative.

Read more about the overall process in what fermentation is and about yeast’s role in what yeast does in wine.

Malolactic fermentation and buttery aromas

Malolactic fermentation, often shortened to MLF, is a process in which lactic acid bacteria convert malic acid into lactic acid. It changes more than acidity: it can also affect aroma and texture.

A well-known example is diacetyl, a compound that can contribute buttery, creamy or butterscotch-like notes. At modest levels, these characters may sit comfortably within a wine’s style. At higher levels, the same butteriness may become distracting or be considered a fault.

But butter does not prove that MLF took place. A wine may undergo MLF without showing an obvious buttery aroma, and other wine characteristics can mask or modify it.

That distinction is useful when tasting: describe what you smell first, then consider possible causes. Do not work backwards from one descriptor as though it were a production record. For a fuller explanation, see what malolactic fermentation is.

Lees, yeast contact and bread-like characters

After fermentation, wine may remain in contact with lees—the yeast cells and other solids that settle in the vessel. As yeast cells break down, a process known as autolysis, they can release compounds that affect aroma, texture and the way other characters are perceived.

Lees contact or yeast autolysis may contribute impressions such as:

• bread or dough;
• biscuit;
• pastry;
• brioche;
• savoury or nutty nuances.

These descriptors are commonly associated with yeast contact, but they are not universal markers. The result depends on the length of contact, whether the lees are stirred, the vessel, oxygen exposure, wine composition and cellar management.

Lees contact can also create unwanted characters in some circumstances, including sulphury or cheesy notes. That is one reason “secondary” should not be treated as a synonym for “pleasant”.

What about oak?

Oak can contribute vanilla, toast, spice, smoke, coconut or cedar-like impressions. These aromas are certainly connected to a winemaking choice, but their classification varies.

Some tasting frameworks place oak under secondary or post-fermentation winemaking aromas. Other approaches group oak with maturation or treat it separately. The safest learner-friendly description is that oak is winemaking-derived, while its category depends on the framework being used.

This page focuses on fermentation, yeast, malolactic fermentation and lees. For the detail of how wood affects wine, see what oak does to wine.

Secondary aromas versus faults

A secondary aroma is an origin category, not a quality score.

A process-derived character may be:

• attractive and integrated;
• neutral or subtle;
• distracting at high intensity; or
• a sign of a fault or taint when it falls outside the intended style.

Do not automatically classify Brettanomyces, volatile acidity, oxidation, reduction, mousiness or excessive sulphur as ordinary secondary aromas. These can involve microbial, chemical or winemaking processes, but they are better considered separately when they create undesirable characters.

The key question is not simply, “Is this secondary?” It is also, “How intense is it, does it suit the wine, and is the wine balanced?”

How to recognise secondary aromas when tasting

Try this simple sequence:

1. Describe the aroma without explaining it. Is it fruity, floral, yeasty, creamy, bready, toasty, savoury or sulphury?
2. Look for a group of clues. Bread, pastry and creamy texture together may suggest yeast contact more strongly than “bread” alone.
3. Separate possibility from proof. Butter may be consistent with diacetyl, but it does not confirm MLF.
4. Consider the wine’s style and age. Fermentation-derived characters may be obvious in a young wine, integrated with time or partly hidden by fruit and oak.
5. Assess balance. A subtle process-derived aroma may add interest; an overpowering one may dominate the wine.

Australian learners will encounter these characters in many kinds of wine. Australian regions, grape varieties and climates influence the starting material, but they do not create one fixed national or regional secondary-aroma profile. Fermentation, lees contact, malolactic fermentation and maturation choices vary between wines.

The most useful tasting habit is therefore curiosity rather than certainty. Secondary aromas can help you understand how a wine was made, but your nose alone cannot reliably reconstruct its production history.

Frequently asked questions

Are secondary aromas the same as fermentation aromas?

Not always. Many explanations use “secondary aromas” mainly for aromas created during fermentation. Broader tasting frameworks may also include post-fermentation winemaking influences such as lees contact, malolactic fermentation and oak.

Is butter a sign of malolactic fermentation?

It can be associated with diacetyl produced during malolactic fermentation, but butteriness is not proof that MLF occurred. Concentration and wine style also matter.

Is biscuit aroma a sign of ageing?

Not necessarily. Biscuit, bread and brioche notes may be associated with lees contact or yeast autolysis. Ageing can also change how these aromas are perceived.

Are secondary aromas good?

Not automatically. Their desirability depends on intensity, balance and style. A secondary aroma can be attractive, neutral or faulty.