Welcome to the third part of Tasting Analysis Like a Professional. Where the previous parts tackled the method itself and the visual impression, we now turn our gaze (or rather our nose) towards the most astonishing tool you have in tasting analysis: the sense of smell. This is where a wine truly unfolds, and it is here that most of the nuances we call "taste" actually arise.
Aroma is also the hardest thing to put into words. That is why this part is just as much about working systematically and understanding where the aromas come from as it is about learning a long list of descriptors by heart. When you understand the mechanisms behind it, it becomes far easier to recognise what you have in the glass.
What you will learn
- How to smell methodically and get the most out of your nose
- The division into primary, secondary and tertiary aromas, and where they originate chemically
- How to work with aroma families as a practical system
- How to assess intensity and complexity without guessing
How to smell methodically
The sense of smell is surprisingly powerful and surprisingly lazy at the same time. A human being can recognise around 10,000 different smells, and this happens via an olfactory mucous membrane with roughly five million scent neurons. The binding takes place on around 1,000 different receptor proteins on the cells in the nasal passage, which recognise volatile molecules and pass the signal on to the brain. It is this enormous combinatorics that allows a wine to tell us so much.
The practical takeaway you should carry with you: during normal breathing only around 5% of the inhaled air reaches all the way up to the scent receptors, while active sniffing increases that to around 20%. In other words, you get four times as much information by sniffing deliberately and briefly rather than breathing passively over the glass.
The practical routine
Begin with a still glass at rest before you swirl. That gives you the most volatile, light molecules first. Then swirl the glass to release more volatile compounds by increasing the surface area, and sniff again in short, concentrated draws. For a scent molecule to even reach the receptors at all, it requires a combination of lipophilicity, sufficient vapour pressure, reasonable water solubility and a concentration above the perception threshold. That is why temperature and aeration in the glass change the aromatic picture markedly: you shift the equilibrium of which molecules evaporate.
Remember too that scent impressions are not additive in a simple way. Several aromatic substances interact during the brain's processing and can produce integrated, competing or even mutually suppressing effects. That explains why a single dominant note can mask several underlying ones, and why patience pays off.
Primary, secondary and tertiary aromas
The classic division follows the origin of the aromas, and here it is worth being precise. A wine's aromatic substances fundamentally stem from four sources: varietal aromas from the grape itself, prefermentative aromas from the enzymatic breakdown of lipids, fermentative aromas from the metabolism of yeasts and bacteria, and postfermentative aromas from transformations during ageing.
Primary (varietal) aromas
The primary aromas come from the grape and its cultivation. These include monoterpenes, C13-norisoprenoids, methoxypyrazines, thiol compounds and several other volatile classes. A central point at expert level is that a large part of the grape's aromatic potential is bound as glycosides, that is, as a non-volatile reserve that is only released as aromatic aglycones through enzymes, acid or heat during ripening, processing and ageing. That is why a young wine can have "hidden" aromatic potential.
Some compounds are active in free form already in the grape and must. The monoterpene linalool and the methoxypyrazines provide varietal typicity, even though the grape juice itself tastes a little of it. The C13-norisoprenoids are formed by oxidative cleavage of carotenoids and are present mostly as glycosides. Thiol compounds such as 3-mercaptohexan-1-ol occur as cysteine or glutathione conjugates in the must and are released into the free, intensely tropical-smelling form in the wine.
The grassy C6 compounds (prefermentative)
When grapes are crushed in contact with air, lipoxygenases oxidise unsaturated fatty acids with cis,cis-1,4-pentadiene systems into hydroperoxides, which hydroperoxide lyases cleave into C6 aldehydes with green, grassy notes. In practice, however, these aldehydes are reduced to hexanol during fermentation and contribute only a little to the aroma of the finished wine. A good example of why process matters more than the starting point.
Secondary (fermentative) aromas
The yeast Saccharomyces cerevisiae produces ethyl and acetate esters, higher alcohols, fatty acids, lactones, sulphur compounds, monoterpenes and benzenoids. Ethyl esters give fruity notes and are formed by esterification of activated fatty acids, where the fatty acid concentration is the limiting factor. Acetate esters, by contrast, are formed by the condensation of alcohol with acetyl-CoA and are governed by the activity of alcohol acetyltransferase. Higher alcohols such as 2- and 3-methylbutanol and 2-phenylethanol contribute to the vinous character.
Malolactic fermentation also belongs here. Oenococcus oeni is the typical bacterial species that converts sharp malic acid into softer lactic acid, which reduces the acidity while also improving microbial stability and aromatic complexity.
Tertiary (postfermentative) aromas
The tertiary aromas arise during ageing and maturation, where the other compounds are transformed. Oxidation plays a role here: acetaldehyde is the wine's most important aldehyde, where small amounts lift the bouquet, while excess gives unwanted sherry-like tones. Esters are sweet-smelling compounds that are formed both during fermentation and maturation and contribute to the bouquet. It is in this interplay between reduction, oxidation and the release of bound compounds that a mature wine's complexity is built up.
The most important aroma families
Aroma families are not a chemical truth but a practical language that helps you structure what you perceive and communicate it onwards. Think of the families as headings, working your way from the general to the specific.
- Fruit: often driven by esters, where ethyl esters give fruity notes. Distinguish between light fruit, dark fruit, stone fruit, citrus and tropical fruit, the last of which often stems from thiol compounds.
- Flowers and herbs: often linked to terpenes found in the skins of aromatic grapes. The green, vegetative notes can come from methoxypyrazines, which, with their extremely low thresholds, mark the aroma even in tiny amounts.
- Spice and roasted tones: typically developed during maturation and barrel ageing, part of the postfermentative picture.
- Yeast and milky: medium to long-chain fatty acids can give milky notes, and the malolactic imprint belongs here.
- Maturation and development notes: the tertiary tones that grow forth with time in the bottle.
When you work with the families, start broad and zoom in. "Fruit" becomes "dark fruit" becomes a more precise association. That is more credible than jumping straight to a very specific descriptor you cannot justify.
Intensity and complexity
Here it is important to distinguish between two things that are often confused. Intensity is about how strong the aroma is, while complexity is about how many different, simultaneously readable layers there are.
The concept that makes intensity tangible is the aroma's perception threshold: the lowest concentration at which a scent can be perceived, established with sensory panels at the 50% detection level via triangle testing. A useful related measure is the odour active value (OAV), the ratio between a compound's concentration and its threshold. The higher the OAV, the greater the aromatic impact a given compound has, regardless of how little of it there may be. The methoxypyrazines are the classic example: with thresholds in the range of a few ng/L, they can decisively mark a wine in amounts that are virtually unmeasurable without specialist equipment.
You assess complexity by registering how many families and layers are actually present, and whether they develop over time in the glass. Remember here that several aromatic substances interact, so a high number of compounds does not automatically give a rich impression. Some effects are suppressing, and a single strong note can dominate. Therefore assess what you actually read, not what you assume ought to be there. A wine's overall aromatic richness ultimately depends on grape, cultivation, ripeness and winemaking, and over 800 different aroma compounds can occur in concentrations from mg/L all the way down to ng/L.
In brief
- Sniff actively and briefly: it quadruples the air that reaches your scent receptors compared with passive breathing.
- The aromas are divided into primary (grape), secondary (fermentation and malolactic) and tertiary (maturation), and a large part of the grape's potential is bound as glycosides.
- Aroma families are a practical language: start broad, zoom in, and justify what you say.
- Intensity is about strength (think thresholds and OAV), complexity about the number of readable layers, and the two are not the same.
Frequently asked questions
Why does a young wine sometimes smell less than it tastes?
Because a large part of the grape's aroma potential is bound as non-volatile glycosides. These aglycones are gradually released through enzymes, acid and heat during ripening and ageing, so the aromatic picture can develop markedly over time.
What does it mean that a scent has a low threshold?
It means that the compound can be perceived at very low concentrations. Methoxypyrazines, for example, have thresholds in the ng/L range, so they can give a clear green or vegetative character even when the amount is minimal.
Ready for the next step?
Once the nose has given you the hypothesis, it is the palate that confirms or refutes it. In the next part, Taste: Structure, balance and finish, we bring together acidity, tannin, body and aftertaste into an overall impression, so your aromatic notes get a counterpart in the mouth.
Feel free to bring out a couple of bottles and smell your way methodically through them as you read on. A selection of organic wines from direct producer relationships is a good place to train your nose. And remember that the best pairing is still the wine you like with the food you like. The rest is practice.