When you gently swirl the wine glass and put your nose close to the rim, have you ever been amazed at the ever-changing aromas of wine, such as strawberry, vanilla, smoke and even leather? These rich aromas are not the magic of winemakers, but the result of a series of complex chemical reactions during the growth, fermentation and aging of grapes.
Why can wine show such amazing diversity in aroma when it is made from the same grapes?
The secret behind this is that wine contains hundreds of different aromatic compounds, which are carried into the air when the alcohol evaporates, forming the various aromas we perceive. However, the content of these aroma molecules in wine is actually very low, with an average of only 1.2 grams of aroma substances per liter of wine. Some are even so tiny that they are difficult to measure even with analytical instruments. However, it is the unique combination of these trace substances that creates the ever-changing aroma characteristics of wine.
From a chemical perspective, the aroma in wine comes from several key compounds:
| Compound Class | Representative flavor | Common grape varieties |
| Esters | Apples, bananas, strawberries | Chardonnay, Pinot Noir |
| Pyrazines | Green pepper, grass, coffee | Sauvignon Blanc, Cabernet Sauvignon |
| Terpenes | Rose, lavender, lychee | Gewürztraminer, Muscat |
| Thiols | Grapefruit, Smoked, Chocolate | Vermentino, Syrah |
Interestingly, the aroma of wine is not static. When we shake the wine glass, this seemingly simple action actually accelerates the contact between the wine and the air, promotes the oxidation reaction, and releases more aroma molecules. This is why professional wine tasting always starts with shaking the glass. However, this rule does not apply to sparkling wine. Excessive shaking will cause the precious bubbles to disappear too quickly, affecting the drinking experience.
Explore the three steps that form the aroma of wine and uncover the evolution of the complete aroma!
Step 1: Natural aroma from grapes
The aromas of different grape varieties vary significantly, giving each variety its own unique “aromatic fingerprint”. For example, Sauvignon Blanc often has distinct grassy and citrus aromas, thanks to the pyrazines it contains, while Gewürztraminer is known for its rich lychee and rose notes, which come from its high terpenoid content. Among red grape varieties, Pinot Noir often exhibits red fruit aromas of strawberry and cherry, while Cabernet Sauvignon is more likely to show black fruit characteristics such as black currant and blackberry.
In addition to the grape variety, the formation of a type of aroma also begins with the grape’s growing season, terroir conditions and climate factors. For example, grapes grown in coastal areas may have mineral or marine aromas, such as white wines from the Chablis region of France. For example, wines from cool climates tend to have more citrus and green fruit aromas, while wines from warm regions tend to develop tropical fruit flavors.
Step 2: Wonderful presentation of winemaker’s skills
When the wine completes the initial fermentation, a series of decisions made by the winemaker, such as whether to use oak barrels, what kind of secondary fermentation to perform, how to deal with the lees, etc., will profoundly affect the aroma profile of the final wine.
1. Use of Oak Barrels
Different types, sizes and degrees of toasting of oak barrels will bring completely different aromatic characteristics to the wine. For example, French oak barrels often impart flavors of vanilla, cedar, and delicate spices to wines, while American oak barrels tend to impart more pronounced notes of coconut and sweet spice.
In addition, the degree to which the oak barrels are toasted during the production process is also crucial: light roasting may retain more of the original wood characteristics, while heavy roasting will produce flavors such as coffee, caramel and even smoke. These changes originate from the thermal degradation of lignin and cellulose during the roasting process, producing a series of aromatic compounds such as vanillin and whiskey lactone (coconut aroma).
2. Malolactic fermentation (MLF)
Converting sharp malic acid to softer lactic acid can produce distinctive aromas such as butter, cream and cheese, which is particularly common in grape varieties such as Chardonnay. This fermentation process can give the wine a rounder taste and more complex aroma layers. Diacetyl is a key compound in this process, which contributes to the attractive aromas of fresh cream and hazelnuts.
3. Aging on lees
When the yeast has completed its fermentation mission, the dead yeast cells (lees) will settle to the bottom of the container. If the wine is left to age on these lees, the yeast autolysis process will release flavors such as bread, biscuit and nuts. Champagne is a classic example of this process, with long-term contact with the lees giving it complex toasted and yeasty aromas.
4. Infection by Botrytis cinerea
When noble rot infects ripe grapes, it dehydrates and concentrates the grapes, while producing compounds such as sotolon, which bring unique flavors such as honey, ginger and dried fruit. Sauternes sweet white and Tokaji noble rot wines are outstanding examples of this process, showing extremely high aromatic complexity and intensity.
Step 3 Aging time allows magical chemical changes to occur quietly
The form and mechanism of this type of aroma is extremely complex, and is mainly the result of long-term interaction between the chemical components in the wine and trace amounts of oxygen. Alcohol, acids, phenolic substances and other substances react with each other to form new compounds, and some of the original aroma molecules will also decompose and reorganize.
This slow oxidation process acts like an invisible winemaker, constantly adjusting and reshaping the aroma profile of the wine. Red wines often develop aromas such as leather, truffles, forest floor and tobacco as they age, while white wines may show characteristics such as honey, nuts and gasoline. For example, after proper aging, high-quality Burgundy Pinot Noir will develop charming flavors of animal leather, earth and mushrooms; while German Riesling sweet white will develop complex aromas of honey and dried fruits.
It is worth noting that the aging potential of different wines varies greatly, and not all wines are suitable for long-term aging. In fact, about 80% of wines have no long-term aging value. Only high-quality wines with sufficient acidity, tannins and alcohol balance can become more elegant with the baptism of time.
To determine whether a wine is suitable for aging, it is necessary to consider multiple factors such as variety characteristics, production area style and brewing process.
Start your journey of scent exploration, starting with the basic scents
When learning to taste the aroma of a wine, you can start by putting your nose close to the glass, taking a deep breath, and trying to find the most obvious fruity or floral aroma. The flavor differences between fruits such as apples, peaches, lemons, and pineapples are quite obvious, and even beginners can distinguish them. As you gain experience you can further distinguish the subtle differences in aroma, such as the aroma of a ripe red apple or a green apple.
At the same time, establishing a personal “aroma memory bank” is also the key to improving recognition ability. For example, in daily life you can consciously smell various fruits, flowers, spices and ingredients, and associate these smell memories with similar aromas in wine, which will help you make more accurate comparisons when tasting wine.
For advanced tasters, you can try to compare the same variety from different production areas or years horizontally to observe how the differences in terroir and year affect the aroma performance. For example, comparing cool-climate versus warm-climate Chardonnay, or New World versus Old World Pinot Noir, can greatly increase your sensitivity to subtle differences in aroma.
The ultimate goal of aroma identification is not to show off one’s ability, but to appreciate the complexity and beauty of wine more comprehensively. When you are able to identify and appreciate the layers and evolution of these aromas, every wine tasting becomes a rich sensory adventure.
