D1C02 The Vine Growth Cycle

Question 1

What is the aim of a grapegrower?

Answer 1

The grape grower’s aim is to produce the largest possible crop of grapes that are of suitable ripeness and quality for the style of wine being produced.

The grape grower therefore needs to manipulate the vine into producing grapes with adequate ripeness of sugar, acids, tannins and aromas/flavours for the wine style being produced.

Question 2

What factors are important for the vine to produce grapes suitable for making wine?

Answer 2

The amount of:

1. heat
2. sunlight
3. water and
4. nutrients
5. (and abundant CO₂)

and the timings of these key resources within the growth cycle, are important if the vine is to produce grapes suitable for making wine.

The grape grower will manage the vineyard to try to compensate for any shortfall or excess in the provision of these resources by the growing environment.

Question 3

What is respiration?

Answer 3

Respiration is the process in which energy is released from food substances, in this case, sugar.

Question 4

What are the 7 stages of the vine growth cycle?

Answer 4

1. Dormancy | Nov - Mar
2. Budburst | Mar - Apr
3. Shoot and Leaf Growth | Mar - July
4. Flowering and Fruit Set | May - June
5. Grape Development | June - Oct
6. Harvest | Aug - Oct
7. Leaf Fall and Dormancy | Nov - Dec

Question 5

What does the vine need during dormancy, and what are adverse conditions?

Answer 5

What the vine needs during this stage:
- Temperatures below 10°C

Adverse conditions:

• Extremely cold temperatures
• Unusually mild temperatures

Question 6

What average air temperatures are too cold for the vine to grow?

Answer 6

Average air temperatures below 10°C are too cold for the vine to grow and therefore in winter the vine is dormant.

Question 7

When does winter dormancy start and end?

Answer 7

With leaf fall in the autumn (November) and ends with budburst in the spring (March).

Question 8

How does the vine support its growth when it cannot photosynthesise, e.g. without leaves?

Answer 8

The vine supports its growth by using stores of carbohydrates, mostly starch, accumulated during the previous growing season in the roots, trunk and branches.

Question 9

What temperature can cause vines to die?

Answer 9

Vines can be severely damaged or killed by temperatures below −15°C.

Temperatures below −25°C will kill most V. vinifera.

Question 10

What vineyard management happens during dormancy?

Answer 10

Winter pruning is carried out

Question 11

Define bud burst

Answer 11

Budburst, also called budbreak, marks the end of winter dormancy. In this process, buds swell and open, and green shoots start to emerge. The timing of budburst depends on a number of factors.

Question 12

What are the vine needs during budburst, and what are adverse conditions?

Answer 12

What the vine needs during this stage:
- Average air and soil temperatures above 10°C

Adverse conditions:

• Frost
• Cold soils

Question 13

What does the timing of budburst depend on?

Answer 13

1. Air temperature (above 10C)
2. Soil temperature (higher = earlier budburst)
3. Grape variety (early budding vs. late budding)
4. Human factors (ex. winter pruning)

Question 14

What climates can be advantegeous for budburst, and why?

Answer 14

Regions that have marked differences in temperature between the various seasons, for example, continental climates.

In these places, the rapidly increasing temperatures in the spring mean that budburst can be relatively uniform and this has positive implications for the homogeneity of later stages in the growing season, potentially eventually leading to a crop of grapes with even ripeness.

Question 15

What climates can be disadvantegeous for budburst, and why?

Answer 15

In regions where there is often less contrast between winter and spring temperatures for example, maritime climates.

Budburst can be less synchronised. Furthermore, problems can occur when a few unusually mild winter days cause early budburst; any cold days and frosts that follow can potentially harm the newly burst buds, leading to lower yields.

Question 16

What soil types are advantageous for budburst in cool climates, and why?

Answer 16

Dry, free-draining soils, e.g. sandy soils

(instead of water-storing soils, e.g. clay-rich soils)

They tend to warm up more quickly than water-storing soils. Higher soil temperatures around the roots => earlier budburst. An early start to the growing season=> better ripening.

Question 17

Define early budding

Answer 17

Grape varieties that require relatively low temperatures at budburst are referred to as ‘early budding’.

Question 18

Give examples of EARLY budding grape varieties.

Answer 18

• Chardonnay
• Pinot Noir
• Merlot
• Grenache.

Question 19

Define late budding grape varieties.

Answer 19

Grape varieties that require higher temperatures are referred to as ‘late budding’.

Because the buds of late-budding varieties need higher temperatures to burst, they are less at risk of spring frosts.

Question 20

Give examples of LATE budding grape varieties.

Answer 20

• Sauvignon Blanc
• Cabernet Sauvignon
• Syrah.

Question 21

What viticultural practices can delay budburst?

Answer 21

Carrying out winter pruning late in the dormant period can postpone budburst, and this technique can be used in areas where spring frost is a known problem.

Question 22

What does the vine need during shoot and leaf growth, and what are adverse conditions?

Answer 22

What the vine needs during this stage:

1. Stored Carbohydrates
2. Warmth, sunlight, nutrients and water

Adverse conditions:

1. Low carbohydrate levels (caused by conditions in the previous growing season)
2. Water stress

Question 23

Define inflorescences.

Answer 23

A cluster of flowers on a stem.

Question 24

What determines the vigour of the vine?

Answer 24

The rate of shoot growth determines the vigour of the vine.

The fastest rate of growth generally occurs between budburst and flowering. The speed of shoot growth can vary between vines and even within different parts of the same vine.

Question 25

How is the initial shoot growth supported?

Answer 25

By carbohydrates stored in the roots, trunk and branches.

Question 26

What effects leaf growth negatively?

Answer 26

Low carbohydrate levels

e.g. from excessive leaf removal, water stress, mildew infections, high crop loads in the previous growing season.

Question 27

What do leaves need for successful growth?

Answer 27

As leaves develop and mature, they provide energy for further growth via photosynthesis, and therefore need adequate warmth and sunlight for this to take place.

Most of the vine’s energy is directed towards shoot growth until flowering starts.

Question 28

What nutrients are needed for vine growth?

Answer 28

Nitrogen (N), potassium (K), phosphorus (P).

Question 29

What can cause stunted (limited) shoot growth?

Answer 29

• water stress
• low nutrients uptake, e.g. very dry soils around the roots

Question 30

What are the effects of stunted (slowed) shoot growth?

Answer 30

Stunted shoot growth can lead to poor quality and lower yields, from:

• small, weak shoots,
• a reduction in leaf number or smaller leaves,
• inflorescences that do not flower properly and/or
• grape bunches that do not ripen fully

Question 31

Name the parts of the vine flower (in the order of fertilisation)?

Answer 31

1. Stamen — (Anther + Filament)
2. Pollen
3. Stigma
4. Pollen tube
5. Ovary
6. Ovule
7. Egg

Question 32

Name the part that attaches a leaf to the plant stem

Answer 32

Petiole

Question 33

Define bud fruitfulness.

Answer 33

The number of inflorescences that will develop from a bud.

Question 34

What can limit bud fruitfulness in the next growing season?

Answer 34

1. Shading of compound buds
2. Low temperatures (under 25°C)
3. Water stress
4. Nutrient deficiency

Given that each inflorescence will become a bunch of grapes, the conditions during this part of the growing season can have a large influence on the next year’s yield.

Question 35

Define flowering

Answer 35

The process of opening of the individual flowers within an inflorescence, from pollination, via germination to fertilization.

Question 36

Describe the initial stage of flowering.

Answer 36

The fused cap of petals known as the calyptra is shed and the pollen-laden stamens (consisting of an anther and filament) are exposed.

Question 37

Describe pollination.

Answer 37

The pollen grains are shed by the pollen-laden stamens and land on the moistened stigma surface.

Question 38

What is germination?

Answer 38

After pollination each pollen grain produces a pollen tube. These pollen tubes penetrate the stigma and then the ovule (the female reproductive cells) in the ovary.

Question 39

Describe fertilization

Answer 39

After pollination and germination, the pollen tube delivers the sperm cells, which fertilise the eggs in the ovule. This leads to the formation of a grape berry.

Question 40

How are seeds formed?

Answer 40

The fertilised ovules form seeds, with up to four per grape. The wall of the ovary enlarges to form the skin and pulp of the grape.

Question 41

What is fruit set?

Answer 41

The transition from flower to grape

Question 42

How are cultivated varieties of vines dissiminated?

Answer 42

Self-pollinating

Research has shown that cultivated varieties of vines are normally self-pollinating (the pollen from the stamens of one flower is transferred to the stigma of the same flower, or a different flower in the same plant). Insects and wind make little contribution to pollination in grapevines.

Question 43

What does the vine need during flowering and fruitset, and what are adverse conditions?

Answer 43

What the vine needs during this stage:

• Warm temperatures (minimum 17°C/63ºF)
• Sunlight, warmth, water and nutrients for bud fruitfulness in the next growing season

Adverse conditions:

• Rainy
• Cloudy
• Windy
• Cold temperatures

Question 44

Within what period does flowering typically take place after budburst?

Answer 44

Within eight weeks of budburst.

However, this timing is extremely temperature dependent, with warm conditions leading to earlier flowering.

Question 45

What conditions are favourable for successful flowering?

Answer 45

Warm conditions (minimum temperature of 17°C) are favourable for successful flowering. With such temperatures, an individual inflorescence can flower within a few days.

Question 46

What conditions are UNfavourable for successful flowering?

Answer 46

Low temperatures can lengthen the duration of flowering, with weeks passing between the earliest and latest flowering. This has a consequential negative effect on the evenness of ripening.

Question 47

How many flowers become grapes?

Answer 47

Not all flowers become grapes. Typically, 30 per cent of flowers will become grapes, but this can range from zero to 60 per cent.

Question 48

What is the optimal temperature for pollen germination and pollen tube growth ?

Answer 48

26–32°C

Question 49

What are negative factors affecting fruit set?

Answer 49

1. Pollen tube growth is negatively affected by cold, rainy and/or windy conditions and this can result in irregular fruit set and is a key cause of poor yields in cool climates.
2. Hot, dry, windy conditions leading to water stress in the vine can also have a negative effect, again leading to reduced yields.

Question 50

Define coulure.

Answer 50

A condition of the grape bunch in which fruit set has failed for a high proportion of flowers. This occurs when ovule fertilisation is unsuccessful, and therefore no grape develops.

Some coulure is normal; however, excessive coulure can reduce yield dramatically.

Question 51

What is coulure caused by?

Answer 51

Coulure is caused by an imbalance in carbohydrate levels.

• This can result from low rates of photosynthesis, which may be caused by cold, cloudy conditions or hot, arid conditions with high water stress (the vine stops photosynthesis to retain water).
• It can also result from vigorous shoot growth diverting carbohydrates from the inflorescence. Very fertile soils, heavy application of fertilisers and vigorous rootstocks can all cause strong shoot growth and therefore lead to coulure.
• Some grape varieties are also naturally more susceptible to coulure than others; Grenache, Cabernet Sauvignon, Merlot and Malbec are all very susceptible.

Question 52

Which grape varieties are susceptible to coulure?

Answer 52

Grenache, Cabernet Sauvignon, Merlot and Malbec.

Question 53

What is millerandage?

Answer 53

A condition of the grape bunch in which there is a high proportion of seedless grapes. The seedless grapes can still ripen normally, but are smaller than grapes with seeds.

Question 54

What are the effects of millerandage?

Answer 54

The smaller grapes from Millerandage may reduce the volume of wine that can be produced.

Some seedless grapes stay small, green and unripe, which can be negative for wine quality.

Question 55

What kind of weather promotes millerandage?

Answer 55

Millerandage can result from cold, wet, windy weather at pollination and fruit set, with some varieties, such as Chardonnay and Merlot, being more susceptible than others.

Question 56

Which grape varieties are susceptible to millerandage?

Answer 56

Chardonnay and Merlot.

Question 57

What 4 stages is grape development typically split into?

Answer 57

1. Grape berry formation
2. Véraison
3. Ripening
4. Extra-ripening

Question 58

What does the vine need during grape development, and what are adverse conditions

Answer 58

What the vine needs during this stage:

1. Sunlight
2. Warmth
3. Mild water stress

Adverse conditions:

1. Too much water and nutrients
2. Excessive shading of grapes
3. Very cold or very hot conditions throughout the day and night

Question 59

What happens during grape berry formation? (6)

Answer 59

1. Hard green grapes grow in size
2. Tartaric and malic acids accumulate
3. Tannins accumulate promoted by sunshine on the grapes and are very bitter at this time.
4. Some aroma compounds + precursors develop
5. Sugar levels are low throughout this stage
6. Water flow into the grape is high at this stage and it is mainly transported to the grape by the xylem

Question 60

Define aroma precursors

Answer 60

Compounds with no aroma that will become aroma compounds during the fermentation process.

Question 61

What are the characteristics of methoxypyrazines?

Answer 61

Methoxypyrazines contribute to herbaceous aromas/flavours in some wines, such as those made from Sauvignon Blanc, Cabernet Sauvignon and Cabernet Franc.

Question 62

Define the xylem.

Answer 62

Xylem is a type of transport tissue that transfers water and some nutrients from the roots to other parts of the vine.

Question 63

What can prolong the stage of grape berry formation?

Answer 63

Too much water and nitrogen can prolong this stage, as these factors encourage shoot growth in preference to grape ripening.

This causes a delay in the onset of the ripening stage and could mean that there is not sufficient time for ripening before the weather becomes cold and rainy and the grapes need to be harvested.

Question 64

What can speed-up the grape berry formation stage?

Answer 64

Mild water stress can speed up this stage and lead to the production of smaller grapes, reducing juice yield but leading to greater skin to pulp ratio, which in red wines can be associated with better quality (higher levels of colour, tannins and aroma compounds).

Grape growers may monitor and manage water levels at this time through irrigation to influence grape formation.

Question 65

What happens to shoot growth during the grape berry formation stage?

Answer 65

Shoot growth continues through this stage, but usually more slowly than earlier in the growing season.

Question 66

What and when is the lag phase?

Answer 66

When grape growth slows down for a few days before véraison.

Question 67

What happens during veraison? (3)

Answer 67

1. The grape cell walls become more stretchy and supple
2. green-coloured chlorophyll in skin cells is broken down; and
3. grapes of black varieties start to become red in colour due to the synthesis of compounds called anthocyanins.

Question 68

Define anthocyanins.

Answer 68

Anthocyanins are the most important natural colourants in wine grapes. Anthocyanins are a group of naturally occurring phenolic-compounds that are responsible for the red, purple and blue colours found in many fruits, vegetables and wine grapes. They belong to a parent group of molecules called flavonoids; they are odourless and virtually have no flavour, contributing to taste a moderately astringent sensation.

Question 69

What is the most important viticultural stage in determining final grape quality?

Answer 69

Ripening

Question 70

What happens during ripening?

Answer 70

1. Shoot growth should have slowed down substantially by this time.
2. The cells in the grape expand rapidly,
3. Sugar and water accumulate
4. Acid levels fall.
5. Tannins, colour and a number of aroma precursors and aroma compounds develop.

Question 71

What are the conditions for photosynthesis to happen at a maximum rate?

Answer 71

Temperatures between 18–33°C and at sunlight levels that are above one third of full sunshine.

Question 72

What slows down rate of photosynthesis?

Answer 72

In years with cold weather or constant cloud, rate of photosynthesis may hinder sugar levels in the grapes.

Question 73

What can cause photosynthesis to slow or stop, and what is the effect?

Answer 73

Very hot, dry conditions that can lead to extreme water stress can cause photosynthesis to slow or stop and hence hinder sugar accumulation in this way.

Question 74

Define the phloem.

Answer 74

Phloem is a type of transport tissue that transfers sugars from the leaves to other parts of the vine.

Question 75

What happens with the xylem water flow during ripening?

Answer 75

During this stage of ripening, water flow via the xylem slows down and a sugar solution is transported by the phloem into the grape.

Question 76

What is the sugar accumulation within the grape correlated to?

Answer 76

The movement of the sugary solution from the phloem into the grape, and hence the sugar accumulation within the grape is correlated to the rate of grape transpiration.

(Grapes do not have stomata and do not transpire as much as leaves, but a small amount of water can transpire through the grape skin).

Question 77

What is the effect of warm, dry conditions on sugar levels, and why?

Answer 77

Grape transpiration and therefore sugar accumulation is faster in warm, dry conditions than cool, humid conditions.

In warm conditions, this accumulation of sugar can be too rapid and reach high levels before aromas/flavours and tannins have developed fully.

Question 78

What happens with tartaric acid during ripening?

Answer 78

The total amount of tartaric acid in the grape generally does not change; however, its concentration falls during ripening due to dilution, as sugar and water accumulate in the grape.

Question 79

Does the total amount of tartaric acid in the grape change?

Answer 79

It falls even further than that of tartaric acid. Because malic acid can be used in respiration during the ripening stage (before this point, sugar is used in respiration).

Question 80

Why do wines from cooler climates tend to have higher natural acidity?

Answer 80

Respiration is slower at cool temperatures than warm ones and this is why wines from cooler climates tend to have higher natural acidity.

Question 81

Define respiration

Answer 81

The process in which energy is released from food substances (ex, sugar)

Question 82

What can lead to a rapid loss of acidity?

Answer 82

Mean temperatures above 21°C in the final month of ripening can lead to a rapid loss of acidity (and a rise in pH)

Question 83

What can reduce acid loss?

Answer 83

Mean temperatures below 15°C can reduce acid loss to a point that acidity levels in the must are too high.’

Uittreksel van: WSET London school. ‘D1 Wine Production’. Apple Books.

Question 84

Why can warm areas with a high diurnal range (e.g. Central Otago, Washington State) produce wines with higher acidity than those with warmer night time temperatures?

Answer 84

Cool night time temperatures mean that less malic acid is lost during respiration.

Question 85

What happens with methoxypyrazine levels during ripening?

Answer 85

During ripening, methoxypyrazine levels fall, but cool temperatures and limited sunlight (e.g. due to excessive shading of bunches) can hinder this decrease and the resulting wines may show particularly herbaceous aromas/flavours.

Question 86

What happens with aroma compounds during ripening?

Answer 86

(Other than methoxypyrazine) aroma compounds and aroma precursors increase during the ripening stage.

The influence of grape variety and natural resources such as heat and light (or indeed other climatic or viticultural factors) on the synthesis of different aroma compounds and aroma precursors is incredibly complex. The range of different aroma compounds and precursors that can be found in grapes is huge, and the synthesis, degradation or retention of each of these compounds may be influenced by heat and light in a different way.

Question 87

What aromas do terpenes give?

Answer 87

fForal and citrus aromas such as the grapey aromas found in Muscat.

Question 88

Although it is difficult to make a direct link between ripening conditions and aroma compounds in the grapes, what kind of aromas are produced in warmer, sunnier climates?

Answer 88

Broadly speaking, warmer, sunnier climates tend to produce grapes and wines with aromas that could be described as ‘riper’ than cooler, less sunny climates.

For example, Chardonnay shows aromas of green and citrus fruit in cool climates and stone fruit and tropical fruit in warm climates.

Question 89

What’s happens with tannin during ripening?

Answer 89

In black grapes, levels of tannins are high at véraison and decrease slightly throughout ripening. The tannins polymerise and this causes them to become less bitter. Sunshine on the grapes promotes tannin accumulation pre-véraison and greater polymerisation post-véraison. In white grapes, tannin levels are much lower.

Question 90

What happens with anthocyanins during ripening?

Answer 90

Anthocyanins increase during the ripening stage, and increase most rapidly with plentiful sunlight and temperatures between approximately 15°C (59°F) and 25°C (77°F).

Question 91

What factors will influence length of ripening stage? (4)

Answer 91

1. Grape variety
2. Climatic conditions
3. Management of the vine and vineyard
4. Time of harvest

• *Ad 1 Grape variety** – Some grape varieties naturally ripen earlier than others. Chardonnay and Pinot Noir are examples of early ripening grape varieties. Cabernet Sauvignon and Grenache are late ripening varieties.
• *ad. 2 Climatic conditions** – Sugar ripening is quickest in warm, dry conditions. However, very hot or dry conditions can cause the vine to shut down, which inhibits grape formation and ripening.
• *ad. 3 Management of the vine and vineyard** – Heavy crop loads, excessive shading within the vine canopy and shoots that are still actively growing can all slow down ripening.
• *ad 4. Time of harvest** – Harvest depends on human factors (desired wine style, logistics) or natural factors (weather such as rain, onset of disease).

Question 94

What happens in the extra-ripening stage?

Answer 94

1. Grapes start to shrivel.
2. No more sugar or water are imported to the grape by the phloem at this stage, but water loss in the grape through grape transpiration means that sugars are concentrated.
3. Extra-ripe aromas can also develop in this stage. This may be desirable in some styles of wine, but not in others.

Grape shrivelling is most likely in hot, sunny, dry climates. In addition, some grape varieties are more susceptible than others (e.g. Syrah is particularly susceptible). The capacity to leave grapes on the vine also depends on weather conditions and disease pressure.

Question 95

What are the key parameters that determine ripeness?

Answer 95

1. The level of sugar
2. The profile of the aromas/flavours in the grapes
3. Tannin ripeness (red wine)

Ad 1. The level of sugar in the grapes is one of the key parameters that determines ripeness. In dry wines, the amount of sugar in the grapes will be directly linked to the alcohol in the wine. In sweet wines, the amount of sugar in the grapes will influence both the sweetness of the final wine and the alcohol.

Ad 2. The profile of the aromas/flavours in the grapes is an important parameter in deciding whether grapes are ready to be harvested. This parameter in particular may be very individual to the grape grower or wine producer and the style of wine that is to be made. In very broad terms, as grapes ripen the aromas tend to change from under-ripe and often herbaceous, to fresh fruit and then to riper fruit, and even jammy or cooked.

Ad 3. Tannin ripeness is another essential parameter in red wine production. During grape formation, skin tannins accumulate but are bitter to taste. During ripening, tannins polymerise and become less bitter. The relationship between the tannin compounds in the grapes and the sensation of tannins in the finished wine is very complex and not well understood. During winemaking and maturation, the tannin compounds that are extracted from the grapes react with other compounds and as part of this their expression may change. Furthermore, even without these reactions, other compounds in the wine can change our perceptions of tannins, for example, a small amount of residual sugar can make tannins appear softer, whereas in bone dry wines with high acidity, tannins can often be perceived as having more astringency. In any case, wine producers are generally looking to avoid bitter unripe tannins, and this will therefore play a part in harvesting decisions.

Question 96

What is considered as optimal ripeness?

Answer 96

What is considered as optimal ripeness (the time at which the combination of the sugar, tannin and aroma ripeness is at its most favourable) will depend on wine style, grape variety, and the preferences of the winemaker, but, ultimately, the aim will be to produce a balanced wine.

If this is not possible naturally, adjustments in the winery can be made. It is easier to adjust sugar, alcohol or acid levels than to work with grapes that have unripe tannins and/or aromas; therefore, many grape growers will focus on attaining the desired level of tannin and aroma ripeness.

Question 97

Define canes.

Answer 97

The green shoots from the previous growing season that have lignified (have turned brown and woody).

Question 98

What happens to the vine in autumn?

Answer 98

leaves fall, carbohydrate reserves are laid down in the roots, trunk and branches and the vine enters its dormant period.