Topic 4 - Growth cycles and fruit development

Question 1

The annual growth of grapevines involves several stages. Summarise these stages:

Answer 1

1. Budburst & early growth
2. Rapid growth & inflorescence initiation
3. Flowering
4. Fruit set
5. Berry development (ripening),
6. Fruit maturity & the post-harvest period
7. Dormancy

Question 2

How do warmer and cooler regions influence the annual growth of grapevines?

Answer 2

In warmer regions, spring will naturally start earlier and all subsequent growth events will also be earlier in a general sense.

Question 3

Varietal differences in annual growth patterns can be substantial. What are some of the earliest developing varieties? What is an example of a later ripening variety?

Answer 3

Some of the earliest developing varieties include Chardonnay and to a lesser extent Pinot Noir.

Cabernet Sauvignon is usually considered a later ripening variety, as an example.

Question 4

What is budburst?

Answer 4

• Budburst occurs when the previously dormant buds begin to grow to produce shoots.
• The buds first start swelling in a process called ‘budswell’. Shoot growth starts slow but speeds up later in spring and continues rapidly until around fruit set.
• Growth of the inflorescence primordia within the compound bud, which has developed during the previous season, initiates again during budswell and continues throughout the budburst process.

Question 5

When does budburst occur?

Answer 5

Budburst usually occurs when the daily temperatures in spring are at least around 10°C.

Question 6

What are factors that can influence the timing of budburst?

Answer 6

1. Atmospheric temperature
2. Variety
3. Soil temperature
4. Rootstock
5. Water stress
6. Timing of winter pruning

Question 7

What is inflorescence initiation?

Answer 7

The period when the inflorescence primordia begin to form is known as ‘inflorescence initiation.

Those primordia committed to becoming an inflorescence represent the fruiting potential or fruitfulness of the vine for the next season.

Question 8

What is an uncommitted primordium?

Answer 8

• As the new shoots grow in spring, compound buds start to develop in the new leaf axils.
• These buds, particularly the primary bud within the compound bud, will become shoots during the next season should they be retained with winter pruning.
• As these new buds grow an uncommitted primordium forms within the compound bud.
• The primordia are called ‘uncommitted’ during this stage because can develop either into an inflorescence or a tendril, depending on environmental and growing conditions.

Question 9

What are the factors that can influence whether or not an uncommitted primordium becomes an inflorescence or a tendril (thus fruitfulness)?

Answer 9

1. Sunlight exposure
2. Temperature
3. Carbohydrate reserves
4. Nitrogen availability

Question 10

How does sunlight influence whether or not an uncommitted primordium becomes an inflorescence or a tendril?

Answer 10

• Exposure of the new buds on young shoots to sunlight increases fruitfulness (stimulates the formation of an inflorescence primordium instead of a tendril primordium).
• In contrast, shading increases the likelihood of the buds forming tendrils.
• Dense canopies, therefore, often aligns with reduced bud fruitfulness the following season.

Question 11

How does temperature influence whether or not an uncommitted primordium becomes an inflorescence or a tendril?

Answer 11

Both too cold and too hot temperatures after budburst could inhibit inflorescence initiation.

However, cold temperatures have more of an impact on reducing fruitfulness.

Question 12

How do carbohydrate reserves influence whether or not an uncommitted primordium becomes an inflorescence or a tendril?

Answer 12

Low levels of stored carbohydrates, especially in grapevine roots, strongly affect the differentiation of inflorescences in young buds.

Low levels of these reserves will lead to more tendrils forming instead of inflorescences.

Higher than optimal fruit yield the previous season or weak vegetative growth (and thus an inferior leaf area) the previous season can cause a reduction in the storage of carbohydrate reserves

Question 13

How does Nitrogen availability influence whether or not an uncommitted primordium becomes an inflorescence or a tendril?

Answer 13

• N deficiency reduces inflorescence differentiation and will lead to more tendrils instead of inflorescences emerging the following season.
• Too much N causes dense canopies, reducing bud fruitfulness for the next season.

Question 14

When the new shoot develops, where will an inflorescence form? Where will a tendril grow?

Answer 14

• When the new shoot develops, an inflorescence forms opposite a leaf.
• Where an inflorescence does not develop, a tendril may grow.

Question 15

How many inflorescences will a fruitful shoot bear?

Answer 15

A fruitful shoot usually bears one to three inflorescences, largely dependent on the growing conditions of the previous season under which the compound bud that produced this new shoot, has developed.

Question 16

How many flowers does an inflorescence contain?

When does flowering normally take place and how long does it last?

Answer 16

An inflorescence contains several to many hundreds of individual flowers.

Flowering normally takes place within six to eight weeks after budburst and lasts for about one to three weeks.

Question 17

What happens when flowering initiates?

Answer 17

Flowering initiates when the flower cap loosens and the caps start falling off to release the stamens (the pollen-producing male reproductive organ)

Question 18

What also occurs during flowering?

Answer 18

Rapid shoot growth takes place during flowering, while root growth usually also peaks around this period.

Question 19

What three factors is the timing and success of flowering largely dependent on?

Answer 19

1. Temperature: you need warm temperatures for flowering to be successful. Timing can also be impacted by temperature.
2. Variety: carieties with earlier budburst, including Chardonnay and Pinot Noir, generally tend to flower earlier as well.
3. Carbohydrate reserves: utilised during flowering, If you a vine has low reserves flowering will be impacted and thus yield.

Question 20

What is fruit set and when does it occur?

Answer 20

Fruit set (or berry setting) signifies the beginning of berry formation.

Fruit set occurs late in spring when rapid shoot growth is still ongoing, shortly after the completion of flowering.

Once the fruit set has occurred, an inflorescence is now known as a bunch and a flower becomes a berry.

Question 21

What are the factors influencing the percentage of fruit set?

Answer 21

• Variety + rootstock – some varieties have a larger % of fruit set. Rootstock may have a minor influence on % of fruit-set.
• Water and nutrient availability (especially N, also B and Zn)
• Carbohydrate reserves and photosynthesis
• Shoot vigour (canopy density)
• Crop load
• Climate (especially temperature)

Question 22

Briefly describe the three stages of berry development.

Answer 22

Berry growth occurs in three stages in a double-sigmoid curve:

1) Rapid initial growth
2) A shorter period of slow growth, also called the lag-phase
3) Another period of rapid growth when ripening occurs

Question 23

Describe ‘Stage 1 - Rapid Growth Phase’ of berry development

Answer 23

– Usually lasts 40 to 60 days
– Characterised by berry cell division and enlargement. Berries can double in size from the start to the end of this period.
– Rapid organic acid accumulation (tartaric and malic acids)
– Tannin accumulation in skins and seeds
– Sugar content of berries remains very low

Question 24

Describe ‘Stage 2 - Lag Phase’ of berry development

Answer 24

– Usually lasts between 14 and 30 days
– Slow berry growth,
– Remain firm but begin to lose chlorophyll, reach peak acid concentration and begin to accumulate sugars slowly
– Ends with veraison signalling the start of the berry ripening period (when berries start softening and with red berries, change colour)
– Shoot growth usually slows down, and should stop by the end of the phase
– Seeds complete most of their development in this stage

Question 25

Describe ‘Stage 3 - Ripening Phase’ of berry development

Answer 25

– Coincides with the beginning of fruit ripening (thus when veraison starts)
– Growth accelerates again, berries start to soften, the acidity decreases, and sugars rapidly accumulate.
– As the berries approach full maturity, berry size reaches a maximum, and sugar accumulation slows. Aroma and flavour complexity increase during the later stages of ripening. The berry doubles in size from the beginning of the lag phase until fruit maturity.
– As the fruit reaches full maturity, the pedicels (which attach an individual berry to the bunch) turn from green to brown.

Question 26

What is the decrease in acidity during ‘Stage 3 - Ripening Phase’ of berry development attributed to?

What sugars accumulate during berry ripening?

Answer 26

– The decrease in acidity during Stage 3 is mostly attributed to malic acid degradation.
– Glucose and fructose are the predominant sugars which accumulate during berry ripening.

Question 27

What is Veraison?

Answer 27

– Veraison is characterised by a reduction in berry skin chlorophyll and an accumulation of phenolic compounds that are responsible for the development of skin colours.
– Yellow to gold colours for white varieties are attributable to flavonols which accumulate in the skins from veraison, while red skins result from anthocyanin accumulation in the skins.

Question 28

What is the rate of sugar accumulation dependent on during the ripening phase of berry development?

Answer 28

The rate of sugar accumulation depends to some extent on the water supply to the vine.

Water stress accelerates the rate of sugar accumulation, while rain or irrigation slows it.

Question 29

Summarize berry composition at the end of stage 3 of berry development.

Answer 29

1. Water
2. Sugars (glucose and fructose)
3. Organic acids (malic and tartaric acids)
4. Phenolic compounds (flavonoids – anthocyanins and tannins; non-flavonoids – derivatives of phenolic acids)
5. N compounds (especially amino acids and proteins – yeast nutrient)
6. Aroma and flavour compounds
7. Minerals
8. Pectins

Question 30

What accounts for the majority of soluble solids in a ripe berry’s juice?

What % of the fresh berry’s weight may be made up of this soluble solid by the time of fruit maturity?

Answer 30

Sugars account for the majority of soluble solids in the berry juice, mostly glucose and fructose in roughly equal amounts.

Sugars increase in concentration during ripening and may reach 25% or more of the fresh berry weight by the time of fruit maturity.

Question 31

What may have a significant effect on the rate of sugar accumulation in berries?

How can this affect the wine made from berries?

Answer 31

• Weather conditions can have a significant effect on the rate of sugar accumulation in berries.
• Unseasonably cool temperatures could slow sugar accumulation, as well as result in higher berry acidity by the time the fruit is harvested.
• During fermentation, yeasts convert these sugars to alcohol and carbon dioxide. The amount of alcohol produced is related to the amount of sugar initially present in the juice before fermentation.

Question 32

What are the main organic acids found in ripe berries accounting for over 90% of the total acids?

What is the ratio between these two acids in the berry juice by the time the fruit is mature?

Answer 32

1. The main acids in berries are malic acid and tartaric acid. Citric acid and some other minor acids are also present.
2. The ratio between malic acid and tartaric acid is usually between 1:1 and 3:1 in berry juice by the time the fruit is mature.

Question 33

What influences the acid composition of berry juice?

Answer 33

Variety, climate and canopy management practices will influence the acid composition of berry juice.

The organic acids generally accumulate during early berry growth, but with the onset of ripening, as sugars accumulate, acid concentrations decrease.

Higher levels of acidity are found in cooler regions. Acidity levels at fruit maturity are negatively correlated with temperature during the ripening period.

Question 34

What are phenolic compounds?

What are two distinct groups of phenolics found in the grapevine berry?

Answer 34

• Compounds that play important roles in determining the colour of fruit and provide most of the characteristics of taste and aging properties in wine.
• Two distinct groups of phenolics found in the grapevine berry are flavonoids including anthocyanins and tannins, and non-flavonoids which are phenolic compounds that are mostly derivatives of phenolic acids such as gallic acid.

Question 35

What are anthocyanins?

Answer 35

Anthocyanins are the pigments responsible for the red colour in the skins of red varieties.

Question 36

What do tannins impact in wine? Where do good and bad tannins come from and how do they influence taste?

Answer 36

Tannins impact wine structure, quality and aging potential, and are associated with bitterness and astringency.

Grape skins, juice and pulp contain ‘good’ tannins whereas the seeds and stems contain ‘bad’ tannins that imparts an overly bitter taste.

Question 37

What are nitrogenous compounds? How are they important during fermentation?

Answer 37

• Grapevine berries contain various N-containing compounds, including amino acids, peptides and proteins.
• N is important as a yeast nutrient during fermentation, affecting the rate of fermentation and production of various secondary products. Insufficient N in the must can cause sluggish or stuck fermentations and the formation of a rotten egg-like odor in the ferment due to the accumulation of hydrogen sulphide.

Question 38

What are aroma and flavour compounds?

Answer 38

A range of aroma and flavour compounds increase in their complexities during the later stages of berry ripening.

Some varieties have specific aroma compounds giving them a distinct varietal character.

Question 39

What are the major aroma compounds?

Answer 39

• Monoterpenes (a floral aroma),
• Methoxypyrazines (green, herbaceous or vegetative aromas),
• Volatile thiols (fruit aromas)
• Rotundone (black pepper type notes).

Question 40

What are minerals often found in grapes? How does the mineral that’s usually most abundant affect wine?

Answer 40

Potassium, sodium, iron, phosphates, sulphate and chloride are minerals often found in grapes.

Potassium is, however, usually the most abundant of these and accumulates during berry ripening. Once accumulating in the berries, potassium leads to the formation of potassium bitartrate, which affects the pH and stability of wine.

Question 41

What are pectins?

Answer 41

Pectin substances are found in the cell walls of the berries.

During ripening, pectin is hydrolysed which allows the berry to soften as it matures.

Question 42

When are grapes considered mature?

Answer 42

– The grapes are considered mature or ripe when the sugar and remaining acids are well balanced.
– The grapes are usually harvested when they have achieved maturity, and maturity is determined by several factors, including the fruit sugar content, acidity, pH, colour and flavour.

Question 43

What other activity happens to grape vines at fruit maturity? What happens in vineyards at this time?

Answer 43

– A second flush of root growth also occurs around or just after the fruit ripening period.
– This stage and the previous stage just after fruit ripening are essential stages for fertilisation in vineyards as the flushes in root growth will coincide with an increased potential for nutrient uptake from the soil.

Question 44

Describe the dormancy phase.

Answer 44

• The dormancy phase occurs in the autumn and is characterised by no growth activity. Dormancy stretches until budburst in spring the following season.
• Dormancy can be categorised into three distinct stages:

1) Acclimation
2) Mid-dormancy
3) Deacclimation

Question 45

Describe acclimation.

Answer 45

– grapevines transition from being non-hardy to fully hardy in preparation to endure the cold winter period.
– begins after the fruit has reached maturity and shoot growth has stopped completely.
– period of cool weather is needed before the vine will go into acclimation, usually in autumn.
– Leaf fall occurs readily during this period.

Question 46

Describe ‘mid-dormancy’

Answer 46

– The period of greatest cold hardiness is when the winter cold is at its peak.
– When grapevines are in this phase, they can withstand temperatures as low as -20°C.

Question 47

Describe ‘deacclimation.’

Answer 47

– Grapevines transition from fully hardy to non-hardy condition and active growth, as a readjustment to warmer temperatures usually late in winter.
– Requires warming of air and soil temperatures
– Carbohydrate reserve remobilisation starts
– Sap flow

Question 48

What occurs in a vineyard during the deacclimation stage of dormancy?

Answer 48

– Pruning is usually conducted during the deacclimation period. The clear presence of moisture within the dormant canes is an indicator that sap flow has restarted, and cutting the canes to look for active sap flow, also called ‘bleeding’, is often useful to determine when grapevines are at an good stage for pruning purposes.

Question 49

What occurs in a vineyard during the deacclimation stage of dormancy?

Answer 49

– Pruning is usually conducted during the deacclimation period.
– The clear presence of moisture within the dormant canes is an indicator that sap flow has restarted, and cutting the canes to look for active sap flow, also called ‘bleeding’, is often useful to determine when grapevines are at an good stage for pruning purposes.

Question 50

The principal organic acids found in the grape berry are:

a) Sulphuric acid and malic acid.
b) Malic acid and acetic acid.
c) Tartaric acid and malic acid.
d) Tartaric acid and nitric acid.
e) Citric acid and tartaric acid.

Answer 50

c) Tartaric acid and malic acid.

Question 51

8. Which of the following is most accurate?

a) After veraison, increases in berry size are largely due to an uptake of water rather than cell division.
b) After veraison, increases in berry size are largely due to an uptake of carbohydrates (sugars).
c) After veraison, increases in berry size are largely due to formation of new cells as the berry grows.
d) After veraison, increases in berry size are due to both an uptake of water and also formation of new cells.
e) After veraison, decreases in berry size are largely due to degradation of organic acids.

Answer 51

b) After veraison, increases in berry size are largely due to an uptake of carbohydrates (sugars).

CHECK ANSWER

Question 52

The most predominant cation found in grape berries is;

a) Sodium
b) Magnesium
c) Potassium
d) Phosphate
e) Nitrogen

Answer 52

c) Potassium

Question 53

Which of the following statements is most correct?

a) As berries ripen the concentration of malic and tartaric acid decreases leading to a drop in pH of the grape juice
b) As berries ripen the concentration of only malic increases leading to a drop in pH of the grape juice
c) As berries ripen the concentration of malic and tartaric acid decreases leading to an increase in pH of the grape juice
d) As berries ripen the concentration of only tartaric acid increases leading to an increase in pH of the grape juice
e) The pH of the grape berry is buffered and so the minor changes in organic acid content do not affect the overall pH

Answer 53

c) As berries ripen the concentration of malic and tartaric acid decreases leading to an increase in pH of the grape juice

Question 54

In grape berries, the most common carbohydrates are?

a) Starch and pectins
b) Maltose and fructose
c) Glucose and fructose
d) Glucose and sucrose
e) Fructose and sucrose

Answer 54

c) Glucose and fructose

Question 55

Sugars and water are both needed to be taken up by the grape berry, but the uptake is different before compared to after veraison. What are the differences?

Answer 55

Before veraison:

• Sugar content of berries remains low

After veraison:

• Acidity decreases, and sugars are rapidly accumulated

Question 56

Complete the following statement:

Sugars are produced in the green leaves of the vine by a light-capturing process known as [BLANK]. The resulting sugars are transported in the [BLANK] of the vascular system into the developing berry where sucrose is converted to [BLANK] and glucose.

Answer 56

1. Photosynthesis
2. Phloem
3. Fructose

Question 57

Why is it that inflorescences can only occur on fixed nodes?

Question 58

The acid content of grape berries is known to vary with region and climate.

What are the acids and which of these changes if comparing a hot versus cool region?

Answer 58

The primary organic acids in berries are malic acid and tartaric acid.

Organic acids generally accumulate during early berry growth, but with the onset of ripening, as sugars accumulate, acid concentrations decrease.

Higher acidity levels are found in cooler regions because acidity levels at fruit maturity are negatively correlated with temperature during the ripening period.

Question 59

Using the space below, draw the typical curve of the changes in grape berry volume over time and indicate the main processes occurring at selected stages.

Answer 59

Berry growth occurs in three stages in a double-sigmoid curve:

1) rapid initial growth, characterised by cell division and enlargement, rapid organic acid accumulation, and tannin accumulation in skins and seeds
2) a shorter period of slow growth also called the lag-phase, characterised by slow berry growth, reaching peak acid concentration and beginning to accumulate sugars slowly, ends with veraison
3) another period of rapid growth when ripening occurs. characterised by berries softening, the acidity decreasing and sugars rapidly accumulating.

Question 60

Identify the main phenolics found in grape berries and describe what role they have.

Answer 60

• Phenolics are compounds that play important roles in determining the colour of fruit and provide most of the characteristics of taste and aging properties in wine.
• Two distinct groups of phenolics found in the grapevine berry are flavonoids including anthocyanins and tannins, and non-flavonoids which are phenolic compounds that are mostly derivatives of phenolic acids such as gallic acid.

Question 61

What grape component is most likely to contribute to the development of bitterness in finished wines?

Answer 61

Seed tannins

Question 62

Why are berry skins important in winemaking?

Answer 62

Colours and tannins are associated with berry skins

Question 63

Which of the following will not be expected to inhibit inflorescence initiation in the compound buds?

A. Nitrogen deficiency
B. Oversupply of nitrogen
C. Intense sunlight exposure
D. Cold temperatures after budburst

Answer 63

C. Intense sunlight exposure

Question 64

Which of the following stages would you consider most suitable in regards to the timing of the practice of leaf removal from the canopy of a grapevine?

A. During fruit set
B. During flowering
C. Just before harvest
D. During the post-harvest period

Answer 64

A. During fruit set

Question 65

Which of the following is not a known detriment to fruit set?

A. Intense sunlight exposure
B. Boron deficiency
C. Zinc deficiency
D. A reduced root carbohydrate concentration

Answer 65

A. Intense sunlight exposure

• Boron & Zinc play important roles in flowering and therefore fruitset
• Inflorescence use carbohydrate, so reduced root carbohydrate concentration will be detrimental

Question 66

Which of the following grape components is most likely to contribute to the development of bitterness in finished wines?

A. Seed tannins
B. Skin anthocyanins
C. Skin tannins
D. Phenolic acids

Answer 66

A. Seed tannins