Section 2 · Factors Affecting the Style, Quality and Price of Wine

The Vine

Every bottle of wine begins with a vine. Understanding how that vine is built, how it grows through its annual cycle, and the critical decisions made about species, rootstock, and clonal material is the foundation for everything else in the WSET Level 3 syllabus. This chapter is about the plant itself, its anatomy, its life cycle, and the biological processes that turn sunlight into sugar and, eventually, into wine.

Vine Species: Why Vitis vinifera Matters

There are many species of vine in the world, but only a handful matter for winemaking. The most important distinction the exam requires you to know is between Vitis vinifera and other species.

Vitis vinifera

This is the main Eurasian species of vine. It produces virtually all of the grapes used in winemaking worldwide and has been cultivated for thousands of years. When you think of Chardonnay, Cabernet Sauvignon, Pinot Noir, Riesling, or any other well-known grape variety, they are all Vitis vinifera.

Vitis vinifera produces wines of far superior quality to other vine species. However, it has a critical weakness: its roots are highly susceptible to phylloxera (covered later in this chapter).

American Vine Species

There are three important American species: Vitis labrusca, Vitis riparia, and Vitis rupestris. These are native to North America. The wines they produce are generally considered to have unattractive flavours (often described as "foxy"), so they are rarely used for winemaking on their own.

However, American species have one enormous advantage: they are resistant to phylloxera. This is why they are used extensively as rootstocks, the roots of an American species are grafted with the fruit-bearing top of a Vitis vinifera vine, combining the best of both worlds.

Hybrids

Hybrids are created by cross-breeding Vitis vinifera with American species. The goal is to combine the flavour quality of vinifera with the disease resistance of American vines. Some hybrids are planted in regions where conditions are too harsh for pure vinifera varieties, but they are generally prohibited in European quality wine production.

Key distinction: Note the difference between a hybrid (a cross between two different species) and a cross or crossing (a cross between two varieties of the same species). Müller-Thurgau, for example, is a crossing of two Vitis vinifera varieties (Riesling and Madeleine Royale), not a hybrid. Crossings are permitted in quality wine production; hybrids generally are not.

Grape Varieties

There are thousands of grape varieties belonging to Vitis vinifera. For the wine consumer, the principal differences between varieties are variations in colour and flavour, with both properties coming from the grape itself. But differences between varieties go beyond taste and appearance, they also affect:

When selecting a grape variety, the grower must consider all of these factors alongside the climate and soil of their vineyard. Planting the wrong variety in the wrong place is one of the most fundamental mistakes a grower can make, no amount of clever winemaking can compensate for a grape that never ripened properly.

How Vines Are Propagated

To preserve the unique qualities of a grape variety, vines cannot be grown from seeds. Seeds produce genetically variable offspring, plant a Pinot Noir seed and you won’t get Pinot Noir. Instead, vines are propagated vegetatively using one of two techniques:

Cuttings

A section of a vine shoot is cut, planted, and encouraged to develop its own root system. The resulting plant is genetically identical to the original. This is the most common method of propagation.

Layering

A cane (a long shoot) is bent down and buried in the ground. The buried section develops roots while still attached to the parent vine. Once established, the new vine is cut from the original plant. This method is slower but can be useful for replacing individual vines in an existing vineyard.

Because vines are propagated vegetatively, every plant of a given variety can theoretically trace its lineage back through a series of cuttings and layerings to a single original plant. A grape variety is therefore a group of individual plants that share the same genetic identity.

Clonal Selection

Although all vines of a given variety are supposed to be genetically identical, small mutations occur naturally over time. Some of these mutations are positive, they might improve fruit quality, increase disease resistance, or adapt better to specific conditions.

When growers identify vines with desirable mutations, they select them for further propagation. This process is called clonal selection. Each individual vine or group of vines that shows a particular set of unique characteristics is known as a clone.

The difference between clones is often small, but it can be significant. When growers order new plants from a nursery, they will often specify which clone they want as well as the grape variety. For example, there are dozens of different Pinot Noir clones, each with slightly different characteristics, some produce smaller berries (more concentrated wine), some are more disease-resistant, some ripen earlier or later.

Clones in practice: Many top producers plant multiple clones of the same variety in their vineyards. This adds complexity to the final wine (because each clone contributes slightly different characteristics) and provides insurance against problems that might affect one clone more than another.

Creating New Varieties

Researchers create genuinely new grape varieties through cross-fertilisation. Pollen from the male part of one vine’s flower is transferred to the female part of another vine’s flower. The resulting grape contains seeds that, when planted, produce a new variety with characteristics from both parents.

Examples include Pinotage (Pinot Noir × Cinsaut, created in South Africa) and Müller-Thurgau (Riesling × Madeleine Royale, created in Germany). These are crossings within Vitis vinifera, not hybrids.

The Anatomy of the Vine

Vine Anatomy Diagram

soil line Roots Trunk Arms (cordons) Shoots Leaves Bunches Tendrils

All vines share a similar structure. Understanding the parts of the vine helps you understand vineyard management decisions (covered in Chapter 6) and how the vine produces fruit. The vine can be divided into four sections: the green parts, one-year-old wood, permanent wood, and the roots.

The Green Parts

These are the parts of the vine that grow each new year. They are the living, active engine of the plant:

Shoots

The principal green structure. Shoots grow from buds each spring, extending rapidly upward. Along the length of each shoot, you’ll find leaves, buds, tendrils, and flower or fruit clusters. By the end of the growing season, shoots turn woody and become one-year-old wood (called "canes").

Leaves

The plant’s engine. Leaves are responsible for photosynthesis: the process by which the vine uses sunlight to convert water and carbon dioxide into glucose (sugar) and oxygen. This glucose is used to support vine growth and, critically, to ripen the grapes. Without healthy, sun-exposed leaves, grapes cannot ripen.

Tendrils

Vines are climbing plants and cannot support themselves. Tendrils are coiled structures that reach out and grab onto supporting structures, a trellis wire, a stake, a nearby branch. Once a tendril grips something, it winds itself tightly to hold the shoot upright. In the vineyard, this natural behaviour is managed through training systems.

Flowers and Berries

Flowers are the vine’s reproductive organs. Each flower contains both male and female parts, and flowers are grouped in clusters called inflorescences. Each flower that is successfully pollinated will become a berry, and the cluster of berries that forms will be the bunch of grapes harvested at the end of the season.

Buds

Buds form at the join between the leaf and the shoot (the "node"). They are compound structures, each bud contains in miniature all the structures that will become the shoot, leaves, flowers, and tendrils the following year. Buds are formed during the current growing season but don’t open until the following spring. This is why damage to buds (from frost, disease, or poor pruning) directly reduces next year’s crop.

One-Year-Old Wood

Shoots turn woody during winter. The following spring, they become one-year-old wood, and the buds that formed on them the previous year burst to grow new shoots. Managing one-year-old wood is vital for the grower because vines will normally only produce fruit on shoots that grow from buds on one-year-old wood.

Every winter the vine is pruned, and the one-year-old wood is either kept as a cane (long, with up to 8–20 buds) or a spur (short, with only 2–3 buds). This pruning decision is one of the most important annual management choices, it directly controls the number of shoots and therefore the potential yield.

Permanent Wood

This is wood that is more than one year old. In the vineyard, the amount of permanent wood is restricted by pruning. The permanent wood makes up the trunk and, where present, the arms (also called "cordons") of the vine. Not every vine has arms, the configuration depends on the training system used (see Chapter 6).

The Roots

Roots anchor the vine in the soil, absorb water and nutrients, and store carbohydrates (energy reserves) that allow the vine to survive winter dormancy and power the initial burst of growth in spring. In modern vineyards, most Vitis vinifera vines are grafted onto rootstock systems from American species, because vinifera roots cannot resist phylloxera.

How the Vine Creates Sugar: Photosynthesis

Photosynthesis is the single most important biological process in viticulture. It is the mechanism by which the vine converts sunlight into the sugar that eventually becomes alcohol in wine.

The process works like this: the vine’s leaves capture sunlight energy and use it to combine water (absorbed through the roots) with carbon dioxide (absorbed from the air through tiny pores in the leaves called stomata). The result is glucose (a sugar) and oxygen (released back into the air).

The equation: Water + Carbon Dioxide + Sunlight → Glucose + Oxygen. This glucose is transported to the grapes during ripening, where it accumulates as sugar. During fermentation, yeast converts this sugar into alcohol and CO₂. So, in a very real sense, wine is bottled sunlight.

For photosynthesis to work efficiently, the vine needs:

This is why canopy management (Chapter 6) is so important. A vine with too many shaded leaves, or too few leaves relative to its crop, will not photosynthesise efficiently enough to ripen its grapes properly.

The Annual Vine Cycle

The vine follows a predictable annual cycle. Each stage of this cycle has implications for the quality and style of the eventual wine. Understanding this cycle is essential for the exam, many questions about vineyard management or vintage conditions are really asking you to connect a stage in the vine cycle to its effect on the final wine.

Winter Dormancy (November–March in Northern Hemisphere)

After harvest and leaf fall, the vine enters dormancy. Growth stops entirely. The vine survives on stored carbohydrate reserves in its roots and permanent wood. This is when winter pruning takes place, the grower removes most of the previous year’s growth, selecting which canes or spurs to keep for the following season.

Extreme cold during dormancy can damage or kill vines. Most Vitis vinifera varieties can survive temperatures down to around -20°C, but prolonged extreme cold or sudden temperature drops are dangerous. In very cold regions (like parts of Canada), vines may be buried under soil for winter protection.

Budburst (March–April)

When soil and air temperatures rise above roughly 10°C, the buds on the one-year-old wood begin to swell and open, pushing out tiny green shoots. This is budburst: the vine waking up after winter.

The danger: Spring frost. Young shoots are extremely vulnerable to freezing temperatures. A single frost event after budburst can destroy an entire year’s potential crop. This is why early-budding varieties (like Chardonnay and Pinot Noir) are riskier in frost-prone sites than late-budding varieties.

Flowering (May–June)

About 6–8 weeks after budburst, tiny flowers appear on the shoots. Grape vine flowers are small and inconspicuous (they don’t need to attract pollinators, they are self-pollinating). Flowering is a critical period because each successfully pollinated flower will become a grape berry.

What can go wrong: Cold, wet, or windy weather during flowering causes two problems:

  • Coulure: poor fruit set. Flowers are not pollinated and fall off the vine, dramatically reducing the number of berries per bunch. This cuts yield.
  • Millerandage: uneven fruit set. Some berries in the bunch develop normally while others remain tiny, seedless "shot berries." This produces uneven ripening within the same bunch.

Ideal flowering conditions are warm, dry, and still. The weather during flowering is one of the first strong indicators of how large the vintage will be.

Fruit Set (June)

After successful pollination, the fertilised flowers begin developing into small, hard, green berries. This is fruit set. At this point, the number of berries per bunch is largely determined. The berries are high in acid and very low in sugar, they are not yet ripe.

Véraison (July–August)

Véraison (pronounced "veh-RAY-zohn") is one of the most important moments in the vine’s cycle. It is the onset of ripening, the point at which the berries change colour. Red grapes turn from green to purple; white grapes turn from green to translucent yellow-green.

At véraison, the berries begin to soften and swell, sugar levels start to rise rapidly, and acid levels begin to fall. The vine shifts its energy from growth (producing new shoots and leaves) to ripening its fruit. From véraison onwards, the grapes are accumulating sugar through photosynthesis.

Véraison does not happen to every berry at exactly the same time, there is usually some variation within a bunch and across the vineyard. Even ripening is a sign of good vineyard management.

Ripening (August–October)

After véraison, the grapes continue to ripen. During this period:

  • Sugar levels rise: through ongoing photosynthesis and transport of glucose to the berries
  • Acid levels fall: acids are broken down by the vine’s metabolism (a process called respiration), especially in warm conditions
  • Flavour compounds develop: the complex aromatic precursors that give each grape variety its character
  • Tannins mature: in red grapes, the tannins in the skins become less harsh and more supple
  • Colour deepens: anthocyanins (colour pigments) accumulate in the skins of red grapes

The grower’s goal is to achieve full physiological ripeness: the point at which sugar, acid, tannin, and flavour are all in balance. In cool climates, the challenge is achieving enough sugar and ripe tannins before autumn weather deteriorates. In warm climates, the challenge is the opposite: preventing sugar from rising too fast while acids fall away, which would produce unbalanced wines (high alcohol, low freshness).

Harvest (September–November)

The grower decides when to pick based on the balance of sugar, acid, tannin, and flavour development. Picking too early produces green, unripe, high-acid wines. Picking too late risks overripeness (high sugar/alcohol, low acidity, jammy flavours), rot, or rain damage.

The timing of harvest is one of the most consequential decisions in wine production. It is covered in more detail in Chapter 6 (Vineyard Management).

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Exam Angle

The vine cycle comes up in many different question types. If you’re asked about vintage conditions, spring frost, flowering failure, or ripening challenges, you need to connect the specific stage of the cycle to its impact on the wine. For example: "Cold rain during flowering caused coulure, reducing yield significantly" or "A warm, dry autumn allowed full phenolic ripeness, resulting in ripe, supple tannins."

Vine Age and Quality

Young vines (under about 3–4 years) are generally not used for quality wine production. They produce inconsistent fruit and need time to establish their root systems. In most appellations, there are minimum vine age requirements before grapes can be used.

As vines age, several changes occur:

This is why you sometimes see the term "vieilles vignes" (old vines) on French wine labels. While there is no legal definition, it generally implies vines of 35+ years. Many producers believe their oldest vines produce their most complex, concentrated wines.

The trade-off: Old vines produce better grapes but fewer of them. This lower yield is one reason why old-vine wines tend to cost more, less wine is made from the same area of vineyard. Eventually (typically after 50–100+ years, depending on conditions), vines become uneconomic because yields are too low, and they must be replanted.

Phylloxera: The Crisis That Changed Viticulture

Phylloxera (Daktulosphaira vitifoliae) is a tiny insect, an aphid-like pest, barely visible to the naked eye, that feeds on the roots of grapevines. It is native to North America, where local vine species evolved resistance to it over millions of years. But Vitis vinifera, the European wine vine, has no natural resistance.

The Disaster

In the mid-19th century, phylloxera was accidentally introduced to Europe (probably on imported American vine specimens). It spread rapidly through the vineyards of France, then across the rest of Europe and eventually to vineyards around the world. The devastation was catastrophic, millions of hectares of vines were destroyed over the course of several decades. Entire wine regions were wiped out.

Phylloxera attacks the roots of Vitis vinifera vines, causing damage that allows secondary fungal infections to enter. The roots decay, the vine can no longer absorb water and nutrients, and it dies. Once phylloxera is present in the soil, it is virtually impossible to eradicate.

The Solution: Grafting

The eventual solution was grafting. Growers learned that they could take rootstock from American vine species (which are resistant to phylloxera) and graft the fruit-bearing top portion of a Vitis vinifera vine onto it. The American roots resist the pest, while the vinifera top produces normal, high-quality grapes.

Today, the vast majority of vineyards worldwide use grafted vines. Choosing the right rootstock is an important decision because different rootstocks offer different characteristics:

Ungrafted Vines

A few places in the world have never been affected by phylloxera, or have conditions that prevent its spread. In these areas, ungrafted Vitis vinifera vines can still be found growing on their own roots ("own-rooted" or franc de pied):

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Exam Tip

You don’t need to know the specific names of rootstocks, but you do need to understand: what phylloxera is, why it devastated European viticulture, how grafting onto American rootstock solved the problem, and why some regions still have ungrafted vines. This comes up regularly as a short-answer topic.

What the Exam Expects You to Know

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Short Answer Strategy

For questions about the vine, always connect biology to wine quality. Don’t just describe what happens, explain why it matters for the wine. "Véraison marks the onset of ripening; from this point, sugars accumulate and acids decline, determining the eventual balance of the wine" is much stronger than just "véraison is when grapes change colour."

Active Recall Prompts

Close this page and try to answer these from memory: