Ch. 2: Vine Growth Cycle

Question 1

What is the key aim of viticulture?

Answer 1

Produce the largest possible crop of grapes that are suitable ripeness and quality for the style of wine being produced

Question 2

What is a vine like in the wild? What does a vine need to grow?

Answer 2

Natural habitat woodland locations with high competition from other plants=vine can survive on limited natural resources IF:
-Vine has sufficient temperature, sunlight and nitrogen, limiting factor is photosynthesis
-Warmth also necessary for respiration (energy is released from food substances, sugar in this case)

Question 3

What is the vine’s main aim if left unchecked?

Answer 3

grapes are meant to attract birds and other animals (palatable for birds but not for producing wine)

so grape grower needs to mold and manipulate the vine by managing the vineyard (any shortfalls or excesses in the resources that the vine needs to grow/thrive)

Question 4

When does dormancy take place?

Answer 4

Nov-March in Northern Hemisphere,

May-September in Southern Hemisphere

Question 5

What happens during dormancy?

Answer 5

Starts with leaf fall in autumn, ends with budburst in Spring

Vine cannot photosynthesize without leaves, sustains itself using carbohydrates stored in roots, trunk and branches

Winter pruning

Question 6

What does the vine need for dormancy?

Answer 6

Vine needs: temperatures below 10℃/50℉

Question 7

What are adverse conditions during dormancy?

Answer 7

Adverse conditions: extremely cold (severe damage/death below -20℃/-4℉) or extremely mild temperatures

Question 8

When does budburst take place?

Answer 8

March-April Northern Hemisphere,

September to October Southern Hemisphere

Question 9

Describe budburst

Answer 9

Buds swell and open, green shoots emerge

Question 10

What does the vine need during budburst?

Answer 10

average air and soil temperatures above 10℃/50℉

Question 11

What are adverse conditions during budburst?

Answer 11

frost, cold soils

Question 12

Timing of budburst depends on…

Answer 12

AIR TEMPERATURE
Temps above 10℃/50℉
More contrast between seasonal temperatures (ex. Continental climates)advantageous for successful budburst
Rapidly increasing temperatures in spring=budburst relatively uniform=even ripeness
Less contrast between winter and spring temperatures (ex. Maritime climates)=budburst less synchronized
Any cold frosts after budburst can harm newly burst buds

SOIL TEMPERATURE
Higher temperatures around the roots encourages earlier budburst
Dry, free draining soils (ex. sandy) warm up more quickly
Advantageous in cool climates, early start to growing season improves chance of full ripening
Water-storing soils (ex. Clay rich) warm up more slowly

GRAPE VARIETY
Merlot opens at temperatures slightly lower than 10℃/50℉
Ugni Blanc buds open at slightly higher temperatures than 10℃/50℉
Early budding (require relatively low temps): Chardonnay, Pinot Noir, Merlot, grenache
Late budding: needs higher temperatures for budburst: Sauvignon Blanc, Cabernet Sauvignon, Syrah
Less at risk of spring frosts
Early budding does not always mean early ripening (Grenache buds early, ripens late)

HUMAN FACTORS
Winter pruning late in dormant period can postpone budburst–often used in areas where spring frost is a known problem

Question 13

When does shoot and leaf growth take place?

Answer 13

March-July Northern Hemisphere,

September to January Southern Hemisphere

Question 14

Describe shoot and leaf growth

Answer 14

Fastest growth generally occurs between budburst and flowering

Vigor used often to describe vegetative vine growth (shoots, leaves, lateral shoots)

Vigor depends on natural resources available (temperature, water, nutrients); planting material (grape variety, clone, rootstock); presence of disease

Many grape growing choices based on how to best manage vine’s vigor to provide desired yield and quality

Initial shoot growth supported by carbohydrate stores
-Low carbohydrate levels can result from excessive leaf removal, water stress, mildew infections, excessively high yields) in previous growing season
-Most of vine’s energy directed at shoot growth until flowering
-Water stress at this time=limited photosynthesis and shoot growth; nutrient uptake impaired in very dry soils
-Stunted shoot growth=small, weak shoots; reduction in leaf number/smaller leaves; inflorescences do not flower properly/grape bunches do not ripen fully

Question 15

Initial shoot growth is supported by…

Answer 15

Carbohydrate stores
-Low carbohydrate levels can result from excessive leaf removal, water stress, mildew infections, excessively high yields) in previous growing season
-Most of vine’s energy directed at shoot growth until flowering
-Water stress at this time=limited photosynthesis and shoot growth; nutrient uptake impaired in very dry soils
-Stunted shoot growth=small, weak shoots; reduction in leaf number/smaller leaves; inflorescences do not flower properly/grape bunches do not ripen fully

Question 16

What does the vine need for shoot and leaf growth?

Answer 16

stored carbohydrates and warmth, sunlight, nutrients and water

Question 17

What are adverse conditions during shoot and leaf growth?

Answer 17

low carbohydrate levels from conditions in previous growing season and water stress

Question 18

When does flowering and fruit set take place?

Answer 18

May-June Northern Hemisphere
November-December Southern Hemisphere

Question 19

What does the vine need for flowering and fruit set?

Answer 19

Warm temperatures (minimum 17℃/63℉)

Sunlight, warmth, water and nutrients for bud fruitfulness in next growing season

Question 20

What are adverse conditions for flowering and fruit set?

Answer 20

Rainy, cloudly, windy, cold temperatures

Question 21

What happens during flowering and fruit set?

Answer 21

New buds develop at base of the leaf stalks (petiole) on new growing shoots

Prompt Buds produced within growing season, produce lateral shoots

Compound Buds: dormant until following spring, provide shoots for next year
shading , temperatures under 25℃/77℉, water stress, nutrient deficiency=can limit bud fruitfulness in the next growing season
-Riesling can form potentially fruitful buds at low temperatures (good in cool climates)

Question 22

What is flowering? What happens during flowering?

Answer 22

Flowering: opening of the individual flowers within an inflorescence
-Pollen-laden stamens (anther and filament) exposed
-Pollen grains shed, land on moistened stigma surface (pollination)
-Germinate, each pollen grain produces pollen tube
Pollen tubes penetrate stigma and then ovule in the ovary
-Pollen tube delivers sperm cells that fertilize eggs in ovule
-Fertilized ovules form seeds (up to four per grape)
-Ovary wall enlarges, forms skin and pulp of grape

Cultivated vine varieties normally self pollinating (pollen from stamens of one flower transferred to stigma of same flower or different flower in same plant

Question 23

Conditions for successful flowering

Answer 23

Takes place within eight weeks of budburst, extremely temperature dependent

Warm conditions (minimum temperature of 17℃/63℉)=earlier flowering, favorable for successful flowering
-Individual inflorescence can start and finish flowering within a few days

Low temperatures can lengthen duration of flowering=weeks
-Negative effect on evenness of grape ripening

Question 24

What is fruit set? What happens during fruit set?

Answer 24

Ovary wall enlarges, forms skin and pulp of grape (?)

Question 25

Conditions for successful fruit set

Answer 25

Typically 30% of flowers become grapes (ranges from 0-60%)

Pollen germination needs warm temperatures (optimal at 26-32℃/79-90℉)

Pollen tube growth negatively affected by cold, rainy, windy conditions=irregular fruit set, key cause of poor yields in cool climates

Hot, dry, windy conditions leading to water stress negative effect=reduced yields

Question 26

Forms of irregular fruit set

Answer 26

Coulure

Millerandage

Question 27

Coulure

Answer 27

Fruit set has failed for high proportion of flowers

Ovule fertilization unsuccessful, no grape develops

Some coulure normal

Caused by imbalance of carbohydrate levels from low rates of photosynthesis (often from cold, cloudy conditions or hot, arid conditions)

High water stress causes vine to stop photosynthesis to retain water

Vigorous shoot growth can divert carbohydrates from inflorescence
-Very fertile soils, heavy fertilizers, vigorous rootstocks

Grenache, Cabernet Sauvignon, Merlot, and Malbec very susceptible to coulure

Question 28

Millerandage

Answer 28

High proportion of seedless grapes
Can ripen normally, but smaller than grapes with seeds=reduces the volume of wine that can be produced

Some seedless grapes stay small, green, and unripe=negative for wine quality

Can result from cold, wet, windy weather at fruit set
Chardonnay and Merlot more susceptible to Millerandage

Question 29

When does grape development take place?

Answer 29

June-September Northern Hemisphere

December-April Southern Hemisphere

Question 30

What does the vine need for grape development?

Answer 30

sunlight, warmth, mild water stress

Question 31

Adverse conditions for grape development

Answer 31

Too much water and nutrients

Excessive shading of grapes

Very cold or very hot conditions throughout day and night

Question 32

Stage 1 of grape development

Answer 32

=Early Grape Growth

Hard green grapes grow in size

Tartaric and malic acids accumulate

Some aroma compounds and aroma precursors develop (ex. methoxypyrazines)

Tannins accumulate, very bitter (sunshine promotes tannin accumulation)

Sugar levels low

Water flow into grape high (transported to the grape by the xylem-transport tissue that transports water and some nutrients from the roots to other parts)

Mild water stress can speed up this stage→smaller grapes→reduced juice yield but greater skin to pulp ratio→in red wines=better quality (higher color, tannin, aroma compounds)

Shoot growth continues but more slowly

Question 33

Stage 2 of grape development

Answer 33

=Veraison

Grape growth slows for a few days (lag phase)

Grape cell walls more stretchy and supple

Green colored chlorophyll in skin cells broken down

Black varieties start to turn red due to synthesis of compounds called anthocyanins
-synthesis=construction of complex chemical compounds from simpler ones

Question 34

Stage 3 of grape development

Answer 34

=Ripening

Most important in determining final grape quality

Shoot growth should slow down substantially

Cells in grape expand rapidly, sugar and water accumulate, acid levels fall; tannins, color, several aroma precursors and aroma compounds develop

Harvest typically occurs August to September Northern Hemisphere and February-

April Southern Hemisphere

Sugar accumulation rapid at start of ripening, slows toward end
-Sugar produced in vines leaves by photosynthesis→photosynthesis can occur at maximum rate at temperatures between 18-33℃/64-91℉ and sunlight levels above one third full sunshine
-Cold weather or constant cloud can hinder rate of photosynthesis and hence sugar accumulation
-Very hot, dry conditions can cause extreme water stress and slow or stop photosynthesis

Water flow via xylem slows down, sugar solution transported to the grape by the phloem (transport tissue)

Movement of sugary solution into grape correlated to rate of grape transpiration
-Grape transpiration and sugar accumulation faster in warm, dry conditions than cool, humid conditions
-Warm conditions can cause accumulation of sugar to be too rapid, reaches high levels before aromas/flavors and tannins have fully developed

Amount of tartaric acid generally doesn’t change but concentration falls during ripening due to dilution

Concentration of malic acid usually falls further than tartaric acid
-Malic acid can be metabolized in respiration during ripening stage

Respiration slower at cool temperatures=higher natural acidity
-Mean temperature above 21℃/70℉ in final month of ripening=rapid loss of acidity, rise in pH
-Mean temperatures below 15℃/59℉=reduce acid loss, acidity levels can be too high
-Cool nighttime temperatures=less malic acid lost during respiration
–Warm areas with high diurnal range (Central Otago, Washington State)=wines with higher acidity than regions with warmer night time temperatures

Methoxypyrazine levels fall
-Cool temperatures and limited sunshine (excessive shading, cloud cover) can hinder this decrease and resulting wine may be particularly herbaceous

Other aroma compounds/precursors increase: Terpenes (give floral and citrus aromas like grapey aromas in Muscat)

Influence of grape variety and natural resources (ex. Heat and light)
-Difficult to make direct link between ripening conditions and aroma compounds)
-Some aromas more associated with grape varieties grown in cool climates, think Chardonnay (green and citrus fruit in cool climates; stone fruit and tropical fruit in warmer sunnier climates)

In black grapes, tannin levels high at veraison, decrease slightly throughout ripening
-Tannins polymerise, become less bitter
-Sunshine promotes tannin accumulation pre veraison and greater polymerization post veraison

Anthocyanins increase during ripening stage, most rapidly with plentiful sunshine and temperatures between 15℃/59℉ and 25℃/77℉

Question 35

Length of ripening stage depends on…

Answer 35

Grape variety
-Chardonnay/Pinot Noir early ripening; Cabernet Sauvignon/Grenache late ripening
-Zinfandel prone to uneven ripening

Climatic Conditions
-Sugar ripening quickest in warm, dry conditions
-Very hot or dry conditions=vine shuts down

Vineyard Management
-High yields, excessive shading within canopy; shoots still actively growing=can slow down ripening

Time of Harvest
-Depends on human (wine style, logistics) and natural factors (weather, onset of disease)

Question 36

Stage 4

Answer 36

=Extra-Ripening

Grapes left on vine shrivel, water loss through grape transpiration causes sugars to concentrate
Extra-ripe aromas can develop
Shriveling most likely in hot, sunny climates; some varieties more susceptible than others (syrah)
Not always possible to leave grapes on vine–weather conditions, disease pressure

Question 37

Other changes in the vine

Answer 37

Late summer, green shoots lignify→canes

Autumn, leaves fall, carbohydrate reserves laid down in roots, trunk and branches, vine enters dormant period

Question 38

Defining ripeness

Answer 38

grower or producer wants to get grapes ripe for the style of wine being made

Tannin compounds extracted react with other compounds and expression may change; other compounds in the wine can change our perception of tannins
-A little residual sugar=tannins appear softer
-Bone dry wine with high acidity=tannins appear to have more astringency