Assess the role of sunlight in determining grape quality. (2023, Q6)

Question 1

How does sunlight affect sugar levels in grapes?

Answer 1

Sunlight drives photosynthesis, increasing sugar production in leaves and translocation to berries. More sunlight = more sugar accumulation = higher potential alcohol.

Question 2

How does shading (lack of sunlight) affect potassium levels in grapes?

Answer 2

Shaded grapes tend to have higher potassium concentrations. This is often linked to delayed ripening and altered berry metabolism, which allows more K⁺ to accumulate.

Question 3

What is the impact of high potassium on wine acidity and pH?

Answer 3

High potassium can raise juice pH by neutralizing acids (mainly tartaric), even if total acidity remains high. This leads to:
• Lower acidity perception
• Higher pH, which can compromise color stability and microbial safety

Question 4

Why is managing sunlight important for potassium control in the vineyard?

Answer 4

Excessive shading (e.g., dense canopies) can lead to high K⁺ levels and unstable musts with high pH. Canopy management practices like leaf removal improve light penetration and help maintain better acid-pH balance.

Question 5

Why can high potassium in shaded grapes lead to high pH despite high acidity?

Answer 5

Potassium neutralizes acids, forming salts that reduce free hydrogen ions, increasing pH even when total acidity remains high.

Question 6

Which phenolic compounds are influenced by sunlight?

Answer 6

Anthocyanins (color), tannins (structure), and flavonols (co-pigmentation and UV protection).

Question 7

What effect does shading have on phenolic development?

Answer 7

Shaded grapes have lower anthocyanin and tannin content, as shown in studies on Shiraz and Bordeaux varieties.

Question 8

What is the risk of too much sunlight on phenolics?

Answer 8

Excessive sun can overheat berries (>35°C), degrading anthocyanins, causing color loss and “cooked” flavors. Excess flavonols may also add bitterness.

Question 10

What timing of sunlight is ideal for norisoprenoid development?

Answer 10

Moderate exposure around veraison. Late exposure or excessive heat may degrade aroma precursors.

Question 11

What is the difference between free and bound monoterpenes?

Answer 11

Free monoterpenes are immediately aromatic; bound ones are glycosidically linked and released during fermentation or aging.

Question 12

How does sunlight affect monoterpenes in aromatic varieties?

Answer 12

Moderate sun (e.g. 50% defoliation) enhances monoterpene levels. Excess sun can cause volatilization or degradation of aroma compounds.

Question 13

Why is east-side leaf removal preferred in many regions?

Answer 13

East-facing fruit receives gentle morning sun, enhancing aroma development while avoiding heat damage from afternoon (west) sun.

Question 14

How does sunlight affect thiol concentration in grapes?

Answer 14

Moderate sunlight increases thiol precursors, often through thickening of skins. Early leaf removal improves thiol potential in Sauvignon Blanc and Petit Manseng.

Question 15

What risk does excessive sun pose for thiols?

Answer 15

It may cause sunburn and reduce freshness or shift flavor balance toward overripe/tropical, away from desired citrus/gooseberry notes.

Question 16

How does sunlight affect methoxypyrazine levels?

Answer 16

Sunlight degrades methoxypyrazines (e.g. IBMP), reducing green/herbaceous flavors in grapes like Cabernet and Sauvignon Blanc.

Question 17

When and how is leaf removal used to reduce pyrazines?

Answer 17

East-side defoliation at veraison is common in cool climates (e.g. Bordeaux) to encourage degradation of IBMP while avoiding heat stress.

Question 18

What are the sensory risks of excessive sunlight

Answer 18

Sunburned berries may develop bitter, oxidative, or “cooked” flavors, reducing grape quality and fermentation potential.

Question 19

How does sunlight reduce fungal disease in vineyards?

Answer 19

UV rays lower humidity, improve airflow, and directly inhibit spore growth (e.g. Botrytis, powdery mildew). Open canopies reduce disease incidence.

Question 20

Which regions use sunlight to manage rot risk or promote noble rot?

Answer 20

Bordeaux and Tokaj use leaf removal and canopy openness to prevent grey rot or to time Botrytis development under controlled conditions.

Question 21

How does sunlight influence ripening consistency?

Answer 21

Even light exposure helps synchronize veraison and maturation across clusters, allowing uniform harvest timing and better grape quality.

Question 22

How does light exposure affect next year’s yield?

Answer 22

Buds in shaded positions may not develop inflorescences, reducing fruitfulness. Light exposure also promotes cane lignification and winter hardiness.

Question 23

How does sunlight help maintain vine balance?

Answer 23

It prevents excessive vegetative growth by ensuring interior leaves remain photosynthetically active, supporting fruit development over foliage.

Question 24

Where are most aroma precursors located in the grape berry?

Answer 24

Mostly in the skins, though some are also in the pulp. This is why skin contact and careful vineyard management are important for aroma potential.

Question 25

How does sunlight influence aroma compounds in general?

Answer 25

Sunlight promotes the synthesis of aroma precursors (like thiols, terpenes, norisoprenoids), and accelerates the degradation of undesirable compounds (like methoxypyrazines). Moderate exposure increases aroma complexity; excessive sun may degrade sensitive compounds.

Question 26

What are norisoprenoids and why are they important?

Answer 26

Norisoprenoids are aroma compounds derived from the breakdown of carotenoids in grape skins. They contribute floral, fruity, or aged aromas like petrol (TDN) in Riesling, or tea/rose in Syrah.

Question 27

How does sunlight affect norisoprenoid levels in grapes?

Answer 27

Sunlight (especially UV) helps break down carotenoids into norisoprenoid precursors. Moderate exposure around veraison increases their concentration, improving aging potential.

Question 28

What are monoterpenes and what do they smell like?

Answer 28

Monoterpenes are aromatic compounds giving floral and citrus aromas, like rose, orange blossom, or bergamot. Found in Muscat, Gewürztraminer, Riesling, and to a lesser extent, Sauvignon Blanc.

Question 29

What’s the difference between free and bound monoterpenes?

Answer 29

Free monoterpenes are immediately aromatic. Bound monoterpenes are attached to sugar molecules (glycosides) and become aromatic only after fermentation or aging releases them.

Question 30

How does sunlight affect monoterpene levels?

Answer 30

Moderate sunlight increases both free and bound monoterpenes. However, excessive sun can volatilize or degrade free monoterpenes, reducing aromatic intensity.

Question 31

Which viticultural practice enhances monoterpenes without damaging them?

Answer 31

Early-season leaf removal on the east side of the canopy allows gentle morning sun to reach clusters, enhancing monoterpenes while avoiding heat damage from afternoon sun.

Question 32

What are varietal thiols and what aromas do they contribute?

Answer 32

Thiols are sulfur-containing aroma compounds responsible for tropical and citrus notes like grapefruit, passionfruit, and gooseberry. They’re especially important in Sauvignon Blanc.

Question 33

Are thiols present in grapes as aromas?

Answer 33

No — they exist in non-aromatic precursor forms (conjugated to amino acids or sugars) and are released by yeast during fermentation.

Question 34

How does sunlight affect thiol precursors in grapes?

Answer 34

Sunlight increases thiol precursor accumulation by: • Promoting berry skin thickening • Possibly shifting amino acid metabolism • Slightly stressing the vine to boost sulfur-based pathways

Question 35

What canopy management technique boosts thiol expression?

Answer 35

Early leaf removal around flowering or fruit set improves thiol precursors, especially on the east side of the canopy. This is common in Marlborough Sauvignon Blanc production.

Question 36

What do methoxypyrazines smell like, and in which grapes are they found?

Answer 36

They smell like green bell pepper, cut grass, or asparagus, common in Sauvignon Blanc, Cabernet Sauvignon, Merlot, and Carménère.

Question 37

When are methoxypyrazines formed and how do they degrade?

Answer 37

They’re formed early in berry development (pre-veraison) and begin to degrade after veraison, especially with light and heat exposure.

Question 38

How does vineyard management reduce methoxypyrazines?

Answer 38

Leaf removal around veraison (especially on the east side) increases sun exposure and accelerates methoxypyrazine breakdown.

Question 39

Why are some methoxypyrazines desirable?

Answer 39

In small amounts, they contribute freshness or a varietal signature (e.g., subtle grassy notes in Sauvignon Blanc). Excess, however, is considered a flaw in most styles.

Question 40

How does excessive sun affect aroma?

Answer 40

Too much sunlight or heat can: • Volatilize or degrade delicate aroma compounds (especially monoterpenes and thiols) • Sunburn grape skins, leading to oxidative aromas, bitterness, and reduced fermentability

Question 41

What is 3MH and what aroma does it contribute?

Answer 41

3MH (3-mercaptohexanol) is a volatile thiol that gives grapefruit, passionfruit, and guava aromas, especially in Sauvignon Blanc and Petit Manseng.

Question 42

What is 4MMP and what aroma does it contribute?

Answer 42

4MMP (4-mercapto-4-methylpentan-2-one) is a thiol associated with boxwood, cat’s pee, or blackcurrant bud aromas. It’s very potent and found in Sauvignon Blanc and sometimes Syrah.

Question 43

How does sunlight affect the concentration of 3MH and 4MMP in grapes?

Answer 43

Moderate sunlight increases the precursors of both 3MH and 4MMP. This is achieved through berry skin thickening and possibly enhanced sulfur-containing amino acid metabolism. Early leaf removal has been shown to raise precursor levels.

Question 44

Where are thiol precursors located in the grape?

Answer 44

Primarily in the skin. This is why exposure to light (which thickens the skin) and machine harvesting (which breaks the skin) can both increase final thiol concentration in wine.

Question 45

Why are 3MH and 4MMP considered important for wine quality?

Answer 45

They are extremely aromatic at low concentrations and define the tropical/citrus style of wines like Marlborough Sauvignon Blanc. Without them, the wine can seem flat or neutral.

Question 46

What is IBMP, and what aroma does it give?

Answer 46

IBMP (isobutyl methoxypyrazine) gives green bell pepper, asparagus, or cut grass aromas, mainly in Bordeaux varieties like Cabernet Sauvignon, Merlot, and Sauvignon Blanc.

Question 47

How does sunlight reduce IBMP levels in grapes?

Answer 47

IBMP is synthesized early and degrades post-veraison. Sunlight accelerates this degradation, especially when clusters are exposed via leaf removal. UC Davis trials showed significantly lower IBMP in exposed vs. shaded fruit.

Question 48

Why is IBMP considered a flaw in many wine styles?

Answer 48

In high concentrations, it dominates the aroma with unpleasant “green” notes. However, small amounts can be desirable in cool-climate Sauvignon Blanc or for stylistic freshness.

Question 49

Which climate and viticultural strategies help manage IBMP?

Answer 49

• Cool climates: Careful leaf removal around veraison (esp. east side) to expose clusters • Hot climates: Sometimes retain some foliage to avoid losing all varietal identity

Question 50

What is the compound responsible for meaty/savoury aromas in Syrah?

Answer 50

The compound is 4-methylthio-2-butanone (4-MTB), also known as “meaty” thiol. It can give bacon, smoked meat, or umami notes.

Question 51

How might sunlight influence meaty/savoury aromas in Syrah?

Answer 51

Although research is still developing, moderate sunlight exposure seems to enhance the reductive sulfur pathways that generate meaty notes (possibly linked to amino acid precursors like methionine). Open canopies can increase precursor concentration, especially in cooler climates like the northern Rhône.

Question 52

Are meaty notes in Syrah considered positive?

Answer 52

Yes — when balanced, they are seen as a signature of high-quality Syrah, especially in traditional northern Rhône wines (e.g., Côte-Rôtie). Excess can be off-putting, though.

Question 53

What is linalool, and what aroma does it give in wine?

Answer 53

Linalool is a monoterpene that contributes orange blossom, citrus, and floral aromas. It is one of the most important aroma compounds in aromatic varieties like Muscat, Gewürztraminer, and Riesling.

Question 54

What is geraniol, and what aroma does it give in wine?

Answer 54

Geraniol is another monoterpene responsible for rose and geranium notes. It adds floral intensity and is found in Muscat, Gewürztraminer, and to a lesser extent in other aromatic varieties.

Question 55

Are linalool and geraniol present as free aromas in grapes?

Answer 55

They exist in two forms: • Free form (volatile and aromatic) • Bound form (glycosidically linked, non-aromatic until released during fermentation or aging)

Question 56

How does sunlight affect linalool and geraniol concentrations in grapes?

Answer 56

• Moderate sunlight exposure (e.g. early east-side leaf removal) increases both free and bound monoterpenes. • Excessive exposure or heat can volatilize or degrade them, reducing floral intensity.

Question 57

In which grape varieties are linalool and geraniol especially important?

Answer 57

• Muscat Blanc à Petits Grains • Gewürztraminer • Riesling • Found in small amounts in Sauvignon Blanc and Albariño

Question 58

What viticultural practice optimizes linalool and geraniol expression?

Answer 58

Early leaf removal (around fruit set or early veraison), especially on the east side of the canopy, to expose clusters to gentle morning sun while avoiding degradation from afternoon heat.

Question 59

What is the impact of high potassium on wine acidity and pH?

Answer 59

High potassium can raise juice pH by neutralizing acids (mainly tartaric), even if total acidity remains high. This leads to: • Lower acidity perception • Higher pH, which can compromise color stability and microbial safety

Question 60

How does sunlight exposure influence potassium and pH in grapes?

Answer 60

Grapes exposed to moderate sunlight tend to have: • Lower potassium • More favorable pH levels This is due to faster, more balanced ripening and improved acid retention.

Question 61

Why is managing sunlight important for potassium control in the vineyard?

Answer 61

Excessive shading (e.g., dense canopies) can lead to high K⁺ levels and unstable musts with high pH. Canopy management practices like leaf removal improve light penetration and help maintain better acid-pH balance.

Question 62

Why is sunlight considered crucial in viticulture?

Answer 62

It drives photosynthesis, influences sugar accumulation, acidity, phenolic development, aroma, and grape health—all key to wine quality.

Question 63

Why is sunlight management important in sparkling wine production?

Answer 63

Sparkling wines require lower sugar levels; sunlight must be controlled to avoid excess sugar and high alcohol. Harvest usually targets ~10% potential alcohol.

Question 64

How does sunlight influence acidity in grapes?

Answer 64

Sunlight promotes malic acid early in the season but accelerates its breakdown during ripening. Too much sun reduces acidity; too little sun retains high acidity.

Question 65

How is sunlight linked to phenolic and color development?

Answer 65

UV light stimulates tannin, anthocyanin, and flavonol production. Moderate sunlight improves structure and color; excessive sunlight degrades phenolics.

Question 66

What happens when red grapes receive too much sun?

Answer 66

Excessive sun can bleach pigments, reduce anthocyanin synthesis, and lead to bitter, lower-color wines with cooked flavors.

Question 67

How does sunlight affect green aromas in grapes?

Answer 67

It reduces methoxypyrazines (green compounds). Exposure after fruit set helps break them down, improving ripeness and flavor.

Question 68

Why do Marlborough growers remove leaves early around Sauvignon Blanc?

Answer 68

To expose clusters to sunlight, reduce methoxypyrazines, and enhance tropical thiol aromas.

Question 69

What are key vineyard techniques to manage sunlight exposure?

Answer 69

Leaf removal, canopy thinning, shoot thinning, hedging, adjusting row orientation, and choosing the right training system.

Question 70

Leaf removal, canopy thinning, shoot thinning, hedging, adjusting row orientation, and choosing the right training system.

Answer 70

It promotes color and aroma development while protecting grapes from excessive heat, sunburn, and phenolic degradation.

Question 71

How is leaf removal adapted to different climates?

Answer 71

In cool climates, both sides may be exposed; in hot climates, only the morning-sun side is defoliated to avoid overheating.

Question 72

What training systems are used to modulate sun exposure?

Answer 72

VSP in cooler regions for light control; bush vines in hot climates provide natural shading and better air movement.

Question 73

How does crop yield interact with sunlight effects?

Answer 73

Higher yields slow sugar accumulation per berry in sunny years, helping maintain balance in grape composition.

Question 74

How can excessive or insufficient sunlight affect grape quality?

Answer 74

• Excessive sunlight: Acid loss, sunburn, phenolic degradation, bitterness. • Insufficient sunlight: Poor ripening, high acidity, lower phenolics, increased disease risk.

Question 75

What is the structure of the essay: “Assess the role of sunlight in determining grape quality. (2023, Q6)”

Answer 75

• 1. Structure (sugar, acidity, phenolics) • 2. Flavor profile (aromas, sunburn effects) • 3. Vine health (disease resistance, long-term productivity)

Question 76

How does sunlight exposure affect acidity levels in grapes?

Answer 76

• High sunlight = Faster malic acid degradation, leading to lower acidity & higher pH. • Low sunlight = Slower acid loss, higher freshness (e.g., Mosel Riesling retains acidity).

Question 77

What are the risks of high pH in grapes? (2 key consequences)

Answer 77

• 1. Lower microbial stability → Increased risk of spoilage. • 2. Weaker fruit structure → Less aging potential.

Question 78

What is TDN, and how is it influenced by sunlight?

Answer 78

• TDN (1,1,6-trimethyl-1,2-dihydronaphthalene) gives a petrol aroma in Riesling. • High sunlight increases TDN via carotenoid breakdown (e.g., Australian Riesling develops TDN early).

Question 79

Why do Mosel Rieslings have lower TDN compared to Australian Rieslings?

Answer 79

Lower sunlight in Mosel → Less carotenoid breakdown → Minimal TDN in youth.

Question 80

How can excessive sunlight negatively impact flavor compounds? (3 key effects)

Answer 80

• 1. Increased bitterness (flavonol overproduction). • 2. Loss of primary fruit aromas → Dull taste. • 3. Desiccation → Over-concentrated sugars but lower overall quality.

Question 81

How does sunlight influence noble rot formation in botrytized wines?

Answer 81

• Morning mist encourages Botrytis cinerea, but afternoon sunlight dries grapes. • Essential for Sauternes, Tokaj – prevents grey rot (detrimental).

Question 82

How does sunlight affect vine carbohydrate storage and productivity?

Answer 82

• Adequate sunlight supports carbohydrate storage → Higher bud fertility, future yields. • Excessive shading weakens reserves → Lower productivity & inconsistent vintages.

Question 83

Summarize the role of sunlight in grape quality. (3 key areas)

Answer 83

• 1. Structure → Sugar accumulation, acidity, phenolic balance. • 2. Flavor profile → Aromatic compounds, risk of sunburn effects. • 3. Vine health → Disease resistance, long-term productivity.

Question 84

What are the risks of excessive sunlight on grape quality? (4 major points)

Answer 84

• 1. Acid loss → Higher pH, lower freshness. • 2. Phenolic degradation → Weaker color, unbalanced tannins. • 3. Sunburn damage → Bitter flavors, desiccation. • 4. Loss of primary fruit aromas → Lower aromatic expression.

Question 85

How do light-selective shade nets help regulate grape ripening?

Answer 85

Shade nets slow sugar accumulation while preserving acidity, offering a solution for vineyards in warming climates

Question 86

What are the three main viticultural strategies for managing sunlight exposure?

Answer 86

• Canopy management (leaf thinning, shoot positioning). • Shade nets (regulating heat and sun intensity). • Row orientation (optimizing light distribution)

Question 87

What role do shade nets play in climate adaptation?

Answer 87

Light-selective shade nets help preserve acidity, reduce sunburn damage, and mitigate excessive ripening, making them useful for vineyards facing rising temperatures

Question 88

Why is row orientation important in sunlight management?

Answer 88

In warm climates, north-south row orientation distributes sunlight evenly, preventing overexposure on one side of the vine

Question 89

What are the three main ways sunlight affects grape quality?

Answer 89

Sugar accumulation, influencing alcohol and acidity balance. • Phenolic composition, affecting color and tannins. • Aromatic development, impacting freshness and varietal character.

Question 90

Why is sunlight management becoming increasingly important in viticulture?

Answer 90

As climate change increases the risk of excessive sun exposure, vineyard managers must adapt using shading techniques, canopy control, and strategic row orientation to maintain grape quality

Question 91

How are norisoprenoids like TDN formed, and what role does sunlight play?

Answer 91

They are formed from carotenoid breakdown under UV/light exposure. Mid-season sun increases their precursors, contributing to aged aromas like petrol in Riesling.