2.1 Vine Anatomy, Life Cycle & Climate Factors

Vine Anatomy, Phenology & Terroir Climates

Core Sommelier Competency: For the Court of Master Sommeliers (CMS) Certified Examination, a sommelier must possess a deep, mechanistic understanding of how grapevine physiology and climate interact. Every structural component of the vine and every phase of its annual growth cycle directly determines the chemical composition of must—balancing sugars, organic acids, polyphenols, and aroma compounds in the finished glass.

Viticulture is the science, production, and study of grapes. The overwhelming majority of fine wine is produced from the Eurasian grapevine species Vitis vinifera subsp. vinifera. As a perennial, deciduous, woody climbing vine (liana), the vine relies on vegetative and reproductive organs to survive, capture solar energy, and propagate.

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1. Botanical Architecture & Vine Anatomy

Understanding the structural morphology of the vine allows viticulturists to manage yield, canopy microclimate, and disease pressure through precise pruning and training systems.

The Root System & Graft Union

• Root System: In modern viticulture, Vitis vinifera is virtually always grafted onto American rootstocks (Vitis riparia, Vitis rupestris, Vitis berlandieri, or their hybrids) to provide resistance against Phylloxera vastatrix. The root system anchors the vine, absorbs water and essential mineral nutrients (nitrogen, phosphorus, potassium, magnesium, iron), and acts as the primary storage vessel for non-structural carbohydrate reserves (starch) during winter dormancy.
• Graft Union (Bench Graft / Omega Graft): The point of fusion between the scion (V. vinifera fruiting variety) and the rootstock. It appears as a swollen callus slightly above soil level. Deep planting that covers the graft union can cause the scion to throw out its own roots ('scion rooting'), exposing the vine to phylloxera vulnerability.

Permanent Wood vs. Annual Growth

• Trunk: The permanent vertical woody structure supporting the upper architecture of the vine. It acts as the conduit for water and nutrient transport via the xylem (upward vascular flow) and carbohydrate transport via the phloem (downward and lateral vascular flow).
• Cordons (Arms): Horizontal permanent wood extensions of the trunk retained over multiple years. Cordons support spurs in cordon-trained systems (e.g., Cordon de Royat).
• Head: The top of the trunk where canes or spurs originate in head-trained systems (e.g., Guyot or Goblet).
• One-Year-Old Wood: Wood formed during the previous growing season that has lignified (turned woody and brown) over the winter. This wood carries the buds that will burst to produce the current season's fruitful shoots.
  • Cane: A long one-year-old shoot pruned back to typically 8 to 15 buds (Guyot system).
  • Spur: A short one-year-old shoot pruned back to 2 to 3 buds (Cordon system).

Current Season Green Organs

• Shoots: New green growth developing from dormant buds during the spring. As shoots mature through the summer, they lignify into canes via sarmentization.
• Nodes and Internodes: Nodes are the distinct swellings along the shoot from which leaves, tendrils, inflorescences (flower clusters), and lateral buds arise. The smooth stem sections between nodes are internodes.
• Compound Buds (Eyes): Located at each node in the leaf axil. A dormant compound bud contains three distinct pre-formed growing points: the primary bud (which produces the main fruitful shoot), the secondary bud (which emerges if the primary is destroyed by frost, usually carrying 30–50% of the crop), and the tertiary bud (primarily vegetative, emerging only if both primary and secondary fail).
• Leaves: The photosynthetic powerhouses of the vine. Leaves absorb photosynthetically active radiation (PAR, 400–700 nm) to synthesize carbohydrates (glucose) from atmospheric carbon dioxide ($CO_2$) and soil water ($H_2O$), releasing oxygen ($O_2$). The underside of the leaf blade contains stomata, microscopic pores that regulate gas exchange and water transpiration.
• Tendrils: Slender, thigmotropic (touch-sensitive) climbing organs that arise opposite leaves at nodes. Tendrils coil tightly around trellis wires or neighboring vegetation to support shoot uprightness.
• Inflorescences (Flower Clusters): Pre-formed flower groupings that develop opposite leaves on basal nodes (typically nodes 3 to 6). In Vitis vinifera, flowers are predominantly hermaphroditic (perfect flowers having both functional male stamens and female pistils).

Anatomy of the Grape Berry

2. The Annual Phenological Growth Cycle

The grapevine follows an annual biological rhythm dictated by photoperiod (day length) and ambient thermal accumulation. In the Northern Hemisphere, this cycle runs from March through October; in the Southern Hemisphere, it runs from September through April.

 Northern Hemisphere Phenological Timeline:
 [Nov - Feb] Winter Dormancy & Pruning
 [Late Feb - Early Mar] Sap Bleeding (Pleurote)
 [March - April] Budbreak (Débourrement)
 [April - May] Rapid Shoot & Foliage Growth
 [Late May - June] Flowering (Floraison) & Fruit Set (Nouaison)
 [Late July - August] Véraison (Onset of Ripening)
 [September - October] Physiological Ripening & Harvest (Vendange)
 [November] Leaf Fall & Senescence

1. Winter Dormancy (Repos Végétatif)

• Timing: November to February (NH) / May to August (SH).
• Physiology: The vine drops its leaves and enters a state of metabolic inactivity (dormancy) to survive freezing temperatures. The plant protects its tissues by converting soluble starches into sugars, which act as a natural antifreeze inside the woody vascular system.
• Vineyard Operations: Winter Pruning is conducted during dormancy. Pruning establishes the vine's architecture, determines the bud count for the upcoming vintage, controls potential yield, and manages vine vigor.

2. Bleeding of the Vine (Pleurote / Pleurs)

• Timing: Late February to early March (NH) / August (SH).
• Physiology: As soil temperatures rise to approximately 7°C to 10°C (45°F–50°F), root osmotic pressure reactivates. Sap surges up through the vascular system and drips from pruning wounds on canes and spurs. A single vine can exude several liters of clear sap, signaling that the dormant root system has awakened.

3. Budbreak (Débourrement)

• Timing: March to April (NH) / September to October (SH).
• Physiology: When daily mean ambient air temperatures consistently exceed 10°C (50°F)—the biological baseline for Vitis vinifera growth—the protective bud scales separate. The downy woolly bud swell bursts, revealing small green shoot tips.
• Viticultural Risks: Young emerging green tissues have no woody protection and are exceptionally susceptible to spring radiation frosts. Temperatures below -1°C (30°F) kill the primary shoots.

4. Early Shoot & Leaf Development

• Timing: April to May (NH) / October to November (SH).
• Physiology: Shoots grow with extreme rapidity (up to several centimeters per day under warm conditions), fueled initially by stored carbohydrate reserves in the trunk and roots until the new leaves expand and become net photosynthetic exporters of sucrose.
• Vineyard Operations: Shoot thinning (ébourgeonnage), positioning shoots into trellis catch wires, and preventative spraying against powdery mildew.

5. Flowering (Floraison) & Pollination

• Timing: Late May to mid-June (NH) / November to December (SH); roughly 6 to 8 weeks after budbreak.
• Physiology: Inflorescences open. In V. vinifera, the petals are fused into a cap-like protective hood called a calyptra. During flowering, the calyptra detaches at the base and falls away (a process called cap fall), exposing the stamens and pistil. Wind currents and micro-vibrations facilitate self-pollination; grapevines do not require insect vectors.
• Ideal Conditions: Warm, dry, sunny weather with moderate breezes (temperatures between 18°C and 25°C / 65°F–77°F) ensures uniform cap fall and rapid fertilization within 2 to 3 days.

6. Fruit Set (Nouaison) & Physiological Disorders

• Timing: Mid to late June (NH) / December (SH).
• Physiology: Fertilized flowers swell to form small, hard, green berries. Typically, only 20% to 30% of flowers in an inflorescence set into mature berries; unfertilized flowers naturally drop.
• Major Fruit Set Vulnerabilities:
  • Coulure (Shatter): The failure of grape blossoms to develop into berries, causing flowers to drop prematurely from the rachis. Triggered by cold, rainy, overcast weather during flowering, which impedes carbohydrate synthesis, or by excessive nitrogen vigor diverting carbohydrates away from clusters into shoot tips.
  • Millerandage (Hens and Chicks / Shot Berries): Incomplete or uneven fertilization where grape clusters contain a mixture of normal full-sized seeded berries and small, seedless, hard green berries that remain unripe. Triggered by cold snaps, rain, boron deficiency, or grapevine fanleaf virus (GFLV).

7. Véraison (Onset of Ripening)

• Timing: Late July to August (NH) / January to February (SH); roughly 40 to 50 days after fruit set.
• Physiology: The physiological turning point of the annual cycle. The vine shifts from vegetative growth to reproductive maturation:
  • Shoot elongation slows dramatically or ceases altogether.
  • Berries soften and expand due to rapid cellular enlargement.
  • Color Change: Chlorophyll in the exocarp degrades. White varieties turn from opaque dark green to translucent golden-green/yellow; black varieties accumulate anthocyanins, shifting from green to ruby, purple, and blue-black.
  • Sugar & Acid Dynamics: Massive translocation of sucrose from leaves into the pulp, where it hydrolyzes into equal parts glucose and fructose. Concurrently, high concentrations of harsh malic acid are metabolized through cellular respiration, while tartaric acid remains relatively stable.

8. Berry Ripening & Physiological Maturity

• Timing: August to October (NH) / February to April (SH).
• Physiology: The berry continues to accumulate sugars (reaching 18°–26° Brix) while titratable acidity declines and pH rises (from ~2.8 up to 3.2–3.8). Herbaceous green aroma compounds (methoxypyrazines) degrade under solar exposure, while positive varietal aroma precursors (monoterpenes, norisoprenoids) and skin tannins polymerize, losing aggressive bitterness.
• Phenolic Ripeness vs. Technological Ripeness:
  • Technological Ripeness: The optimal ratio of soluble sugars (potential alcohol) to titratable acidity for a target wine style.
  • Phenolic (Physiological) Ripeness: The complete structural maturation of skin tannins, seed lignification (seeds turn from green and astringent to brown and nutty), and degradation of pyrazines.

9. Harvest (Vendange) & Post-Harvest Senescence

• Timing: September to November (NH) / February to May (SH).
• Physiology: Grapes are harvested manually or mechanically based on laboratory analysis and sensory evaluation. Following harvest, the vine utilizes remaining sunlight to synthesize carbohydrates, translocating starch reserves back down into the root system and trunk. With the first autumn frost, chlorophyll breaks down (leaves turn bright yellow or red), abscission layers form at the leaf petioles, leaves drop, and the vine re-enters winter dormancy.

3. Climate Scales & Terroir Influences

In the context of the CMS curriculum, terroir represents the complex interaction of macro-, meso-, and micro-climates with soil composition, topography, aspect, and human viticultural intervention.

Hierarchical Scales of Climate

  +-------------------------------------------------------------+
  | 1. MACROCLIMATE: Regional Climate                           |
  |    (e.g., Bordeaux maritime, Central Otago continental)     |
  |   +-------------------------------------------------------+ |
  |   | 2. MESOCLIMATE: Vineyard Site / Topography            | |
  |   |    (e.g., Corton hill south-facing mid-slope)         | |
  |   |   +-------------------------------------------------+ | |
  |   |   | 3. MICROCLIMATE: Canopy Interior                | | |
  |   |   |    (e.g., Light penetration around fruit zone)  | | |
  |   |   +-------------------------------------------------+ | |
  |   +-------------------------------------------------------+ |
  +-------------------------------------------------------------+

1. Macroclimate: The overarching regional climate of an entire wine region spanning tens to hundreds of kilometers (e.g., the Mediterranean climate of the Napa Valley floor or the maritime climate of Bordeaux). Measured by regional weather stations.
2. Mesoclimate: The localized climate of a specific vineyard site, hillside, or sub-appellation, typically covering a few hundred meters to several kilometers. Heavily modulated by elevation, slope gradient, aspect (compass orientation toward the sun), proximity to localized water bodies, and cold air drainage corridors.
3. Microclimate: The specific atmospheric environment within and immediately surrounding the vine canopy and individual grape bunches (measured across millimeters to centimeters). Influenced directly by vine spacing, canopy management (leaf pulling, shoot positioning), and trellising.

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Major Macroclimatic Classifications

4. Topographic & Environmental Terroir Drivers

Diurnal Temperature Variation (Diurnal Shift)

• Definition: The difference between the maximum daytime temperature and minimum nighttime temperature within a single 24-hour cycle.
• Physiological Mechanism:
  • Daytime Warmth (25°–30°C / 77°–86°F): Drives peak photosynthesis, synthesizing carbohydrates and sucrose transported to berries.
  • Nighttime Cold (10°–15°C / 50°–59°F): The vine dramatically slows cellular respiration. Because cellular respiration consumes organic acids (specifically malic acid), cold nights preserve crisp, bright natural acidity and prevent rapid degradation of volatile aromatic terpenes and esters.
• Wine Impact: Regions with dramatic diurnal swings (e.g., Ribera del Duero, Mendoza, Washington State, Santa Rita Hills) produce wines with high alcohol and intense phenolic pigmentation paired with vibrant, mouthwatering acidity.

Elevation & Altitude

• Lapse Rate: Ambient air temperature decreases by approximately 0.65°C for every 100 meters (or ~3.5°F per 1,000 feet) of elevation gain.
• Ultraviolet Solar Radiation: At high altitudes (e.g., Salta, Argentina at 1,700–3,000m; or Mount Veeder, Napa at 500–700m), atmosphere is thinner, resulting in elevated ultraviolet radiation (UV-B). In response, grapevines synthesize thicker berry skins loaded with higher concentrations of protective anthocyanins and polyphenolic tannins, creating intensely structured, deeply pigmented wines.

Aspect, Slope & Cold Air Drainage

• Aspect (Solar Interception):
  • In the Northern Hemisphere, south- and southeast-facing slopes receive the most concentrated solar radiation, warming earlier in the morning and maximizing daily photosynthetic activity (crucial in cool regions like the Rheingau, Mosel, and Côte d'Or).
  • In the Southern Hemisphere, north- and northeast-facing slopes provide equivalent thermal advantages (e.g., Central Otago, Stellenbosch).
• Slope Gradient & Cold Air Drainage:
  • Cold air is denser and heavier than warm air. On hillside vineyards, cold air naturally drains downslope into the valley floor (an effect called cold-air pooling / frost pockets).
  • The mid-slope (coteau) represents the viticultural sweet spot: it stays warmer than the frost-prone valley floor at night (thermal inversion zone), features thinner, less fertile soils that naturally restrict vine vigor, and provides superior water drainage.

Moderating Water Bodies & Ocean Currents

• Specific Heat Capacity of Water: Large bodies of water (oceans, deep lakes, wide rivers) absorb heat slowly during summer and release it gradually during winter, tempering temperature extremes in adjacent vineyards.
• Famous Temperature-Moderating Currents:
  • California Current (Cold): Originates in the Gulf of Alaska and flows south along the California coast. Meets warm inland air to generate maritime fog banks that pull through coastal gaps (e.g., Petaluma Gap, Templeton Gap, Golden Gate), cooling Carneros, Russian River Valley, and Santa Barbara.
  • Humboldt Current (Cold): Flows north along the coast of Chile, bringing cool marine breezes into the Casablanca, San Antonio, and Leyda Valleys.
  • Benguela Current (Cold): Cools the coastal appellations of the Western Cape of South Africa (Walker Bay, Constantia).
  • Gulf Stream (Warm): Sweeps warm tropical waters past Western Europe, keeping Bordeaux and the British Isles far warmer than their equivalent latitudes in North America.

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5. Heat Summation & Thermal Indices

Viticulturists use mathematical indices to evaluate whether a region provides sufficient thermal energy to ripen specific grape varieties.

The Winkler Index (Growing Degree Days - GDD)

Developed by A.J. Winkler and Maynard Amerine at UC Davis, the Winkler Scale measures heat accumulation during the 7-month growing season (April 1 to October 31 in Northern Hemisphere; October 1 to April 30 in Southern Hemisphere).

$\text{GDD} = \sum_{t=\text{Apr 1}}^{\text{Oct 31}} \max\left(0, \,\bar{T}_{\text{daily}} - 10^\circ\text{C}\right)$

(Where $\bar{T}_{\text{daily}}$ is the average of daily maximum and minimum temperatures in °C. In Fahrenheit, base 50°F is used).