2. The Vine Growth Cycle

Question 1

During what months are vines dormant in the Northern and Southern Hemispheres?

Answer 1

November–March in the Northern Hemisphere
May–September in the Southern Hemisphere

Question 2

During what months is budburst in the Northern and Southern Hemispheres?

Answer 2

March-April in the Northern Hemisphere
September-October in the Southern Hemisphere

Question 3

During what months is shoot and leaf growth in the Northern and Southern Hemispheres?

Answer 3

March-June in the Northern Hemisphere
September-December in the Southern Hemisphere

Question 4

During what months is flowering and fruitset in the Northern and Southern Hemispheres?

Answer 4

May–June in the Northern Hemisphere
November–December in the Southern Hemisphere

Question 5

During what months is grape development in the Northern and Southern Hemispheres?

Answer 5

June-September in the Northern Hemisphere
December-March in the Southern Hemisphere

Question 6

During what months is harvest in the Northern and Southern Hemispheres?

Answer 6

August-October in the Northern Hemisphere
February-April in the Southern Hemisphere

Question 7

At what temperatures do the vines go dormant?

Answer 7

Average air temperatures below 10°C

Question 8

How does the vine sustain itself through dormancy (and the lack of photosynthesis)?

Answer 8

By using stores of carbohydrates, mostly starch, accumulated during the previous growing season in the roots, trunk and branches.

Question 9

Vines can be severely damaged at temperatures below ____ and killed at temperatures below ____.

Answer 9

Vines can be severely damaged or killed by temperatures below −20°C (–4°F). Temperatures below −25°C (−13°F) will kill most V. vinifera.

Question 10

What are the four factors that influence the timing of budburst?

Answer 10

1. Air temperature
2. Soil temperature
3. Grape variety
4. Human factors

Question 11

What average air temperatures are required for budburst?

Answer 11

Average air temperature approximately 10°C

Question 12

How are continental climates advantageous for successful budburst?

Answer 12

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 13

How do soil temperatures influence the timing of budburst?

Answer 13

Dry, free-draining soils, such as sandy soils, tend to warm up more quickly than water-storing soils, such as clay-rich soils, and therefore can be advantageous in cool climates where an early start to the growing season improves the chance of ripening.

Question 14

Give four examples of early budding grape varieties.

Answer 14

Chardonnay, Pinot Noir, Merlot and Grenache

Question 15

Give three examples of late budding grape varieties.

Answer 15

Sauvignon Blanc, Cabernet Sauvignon and Syrah

Question 16

What is an important benefit of late budding grape varieties?

Answer 16

Less prone to spring frost

Question 17

What is a human factor that can delay budburst?

Answer 17

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 18

What does the term ‘vigour’ refer to?

Answer 18

Vegetative vine growth, which includes the growth of the shoots, leaves and lateral shoots, and has implications on the yield and ripening of the grapes.

Question 19

What factors influence a vine’s vigour?

Answer 19

1. The natural resources available to the vine (particularly temperature, water and nutrients),
2. The planting material (grape variety, clone and rootstock)
3. The presence of any disease (e.g. viruses can lower vigour)

Question 20

What can cause a lack of carbohydrates in the vine?

Answer 20

Excessive leaf removal, water stress, mildew infections or excessively high yields in the previous growing season.

Question 21

Why is it important that vines do not suffer water stress through shoot and leaf growth?

Answer 21

Water stress during shoot and leaf growth can limit photosynthesis and shoot growth.
Nutrient uptake through the roots is also impaired in very dry soils.

Question 22

How can stunted shoot growth lead to poor quality and yields?

Answer 22

Stunted shoot growth can lead to 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 23

Name the vine flower part.

Answer 23

Stamen

Question 24

Name the vine flower part.

Answer 24

Anther

Question 25

Name the vine flower part.

Answer 25

Filament

Question 26

Name the vine flower part.

Answer 26

Stigma

Question 27

What factors can limit bud fruitfulness in the next growing season?

Answer 27

Shading of compound buds, temperatures that are too low (under 25°C), water stress and nutrient deficiency can all limit bud fruitfulness (the number of inflorescences that will develop from a bud) in the next growing season.

Question 28

Outline the flowering and pollination process.

Answer 28

1. The pollen-laden stamens (consisting of an anther and filament) are exposed.
2. The pollen grains are shed and land on the moistened stigma surface (pollination).
3. Here, they germinate, with each pollen grain producing a pollen tube.
4. These pollen tubes penetrate the stigma and then the ovule (the female reproductive cells) in the ovary.
5. The pollen tube delivers the sperm cells that fertilise the eggs in the ovule. This leads to the formation of a grape berry.

Question 29

How does the grape berry form after flowering?

Answer 29

After the eggs within the flowers ovule are fertilised by pollen, seeds are formed (up to four per grape).
The wall of the ovary enlarges to form the skin and pulp of the grape.

Question 30

What temperatures are favourable for successful flowering?

Answer 30

Minimum average air temperature of 17°C.

With such temperatures, an individual inflorescence can start and finish flowering within a few days.

Question 31

How do low temperatures affect the flowering process?

Answer 31

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

Question 32

What percentage of flowers become grapes?

Answer 32

Typically, 30 per cent of flowers will become grapes, but this can range from zero to 60 per cent.

Question 33

What temperatures are ideal for pollin germination?

Answer 33

26-32°C

Question 34

How do low temperatures and poor conditions affect fruitset?

Answer 34

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.

Question 35

How do hot, windy and dry conditions affect fruitset?

Answer 35

Water stress can have a negative effect on pollen germination

Question 36

What are the two most common forms of irregular fruitset?

Answer 36

1. Coulure
2. Millerandage

Question 37

What is coulure?

Answer 37

A condition of the grape bunch in which fruit set has failed for a high proportion of flowers.

Question 38

How does coulure occur?

Answer 38

Occurs when ovule fertilisation is unsuccessful and therefore no grape develops.

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

Question 39

What causes coulure?

Answer 39

Coulure is caused by an imbalance in carbohydrate levels.

This can result from:
* low rates of photosynthesis (due to poor conditions, water stress)
* Vigorous shoot growth diverting carbohydrates
from the inflorescence.

Question 40

What is millerandage?

Answer 40

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 41

How does millerandage affect quality and yields?

Answer 41

A high proportion of small, seedless grapes can 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 42

What conditions cause millerandage?

Answer 42

Millerandage can result from cold, wet, windy weather at fruit set.

Question 43

Give two examples of grape varieties particularly susceptible to millerandage.

Answer 43

Chardonnay and Merlot

Question 44

What are the four stages of grape development?

Answer 44

1. Early grape growth
2. Véraison
3. Ripening
4. Over-ripening

Question 45

What is happening inside the grape during early grape growth?

Answer 45

• Grapes grow in size
• Tartaric and malic acids accummulate
• Some aroma compounds and aroma precursors develop (such as methoxypyrazines)
• Tannins accumulate (promoted by sunshine) and are very bitter at this time.
• Sugar levels remain low
• Water flow into the grape is high

Question 46

What is the xylem?

Answer 46

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

Question 47

How do excess water and nitrogen affect early grape growth?

Answer 47

Water and nitrogen 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 cooler and the grapes need to be harvested.

Question 48

How does mild water stress influence early grape growth?

Answer 48

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 49

What is the lag phase in berry development?

Answer 49

Grape growth slows down after early development before véraison.

Question 50

What happens to the grape during véraison?

Answer 50

• The grape cell walls become more stretchy and supple.
• Green-coloured chlorophyll in skin cells is broken down and grapes of black varieties start to become red in colour due to the synthesis of anthocyanins.

Question 51

Outline what happens to the grape during the ripening stage.

Answer 51

• The cells in the grape expand rapidly
• Sugar and water accumulate
• Acid levels fall
• Tannins, colour and a number of aroma precursors and aroma compounds develop.

Question 52

How is sugar produced in the vine?

Answer 52

Sugar is produced in the vines’ leaves by photosynthesis.

Question 53

In what conditions does photosynthesis occur at a maximum rate?

Answer 53

18-33°C
Sunlight levels that are above one third of full sunshine.

Question 54

How do cool, cloudy conditions during ripening hinder sugar development in grapes?

Answer 54

Photosynthesis cannot function at its maximum rate

Question 55

How do hot, dry, windy conditions during ripening hinder sugar development in grapes?

Answer 55

These conditions can lead to extreme water stress which can cause photosynthesis to slow or stop

Question 56

How is sugar transported to the grape during the ripening stage?

Answer 56

Water flow via the xylem slows down and a sugar solution (a mixture of mainly sugar and water) is transported to the grape by the phloem (a type
of transport tissue that transfers sugars from the leaves to other parts of the vine).

Question 57

How do acids develop in the grape during the ripening stage?

Answer 57

• 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.
• The concentration of malic acid usually falls even further than that of tartaric acid.

Question 58

Why do malic acid levels fall quickly during the ripening stage?

Answer 58

Malic acid can be metabolised in respiration during the ripening stage (before this point, sugar is metabolised in respiration).

Question 59

Why do grapes produced in cooler climates have higher acidity?

Answer 59

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

Question 60

At what temperatures do grapes experience a rapid loss of acidity during the ripening stage?

Answer 60

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 61

What temperatures are considered too cool for the final month of ripening?

Answer 61

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

Question 62

Why can regions with a high diurnal range produce wines with higher natural acidity?

Answer 62

Cool night time temperatures also mean that less malic acid is lost during respiration. This is why warm areas with a high diurnal range, such as Central Otago and the wine regions in Washington State, USA, can produce wines with higher acidity than those with warmer night time temperatures.

Question 63

Do methoxypyrazine levels rise or fall during the ripening stage?

Answer 63

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

Question 64

What factors influence the synthesis of aroma compounds and precursers in the ripening stage?

Answer 64

Grape variety
Natural resources (heat and light, etc).

Question 65

Do tannin levels rise or fall during the ripening stage?

Answer 65

Levels of tannins are high at véraison and decrease slightly throughout ripening.

Question 66

What is tannin polymerisation?

Answer 66

A process in which relatively small molecules combine chemically to produce a very large chainlike or network molecule.
Polymerisation of the tannins causes them to be less bitter.

Question 67

How does sunshine influence tannins during grape development?

Answer 67

Sunshine on the grapes promotes tannin accumulation pre-véraison and greater polymerisation post-véraison.

Question 68

What are anthocyanins?

Answer 68

Members of a complex group of natural phenolics responsible for the colour of black and red grapes.

Question 69

In what conditions do anthocyanins most rapidly increase?

Answer 69

Plentiful sunlight and temperatures between approximately 15°C and 25°C

Question 70

What factors influence the length of the ripening stage?

Answer 70

• Grape variety
• Climactic conditions
• Management of the vine and the vineyard
• Time of harvest

Question 71

What occurs in the grape during the over-ripening stage?

Answer 71

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. Extra-ripe aromas can also develop in this stage.

Question 72

What happens to the vine after harvest and leaf fall?

Answer 72

• Green shoots lignify
• Leaves fall
• Carbohydrate reserves are laid down in the roots, trunk and branches
• The vine enters it’s dormant period

Question 73

What four parameters are considered when determining grapes as ‘ripe’?

Answer 73

• The level of sugar
• The level of acidity
• Aroma profile
• Tannin ripeness