葡萄酒社

World of Wine—Seasonal growth cycle

DR CASSANDRA COLLINS:
 

Grape vine development plays a very important role in wine making.
The condition and treatment of the vine during its seasonal growing cycle can have a big impact on grape development and subsequent wine quality.
The major growth stages during the grapevine's seasonal growth cycle are shoot and inflorescence development, flowering, berry development, ripening, and harvest.
These major stages are comprised of many developmental stages starting with the winter bud stage, when the bud is still in a state of dormancy, and finishing with the end of leaf fall.
When these stages occur is dependent on the type of climate, so warm or cool, and the characteristics of the grape variety that is being grown.
When the temperature rises above a critical value, which depends on the variety, buds begin to burst.
This stage is known as bud burst, and occurs earlier in hotter regions than in cool regions and is variety dependent.
Typically, only the primary bud in the dominant bud becomes active in the spring.
The secondary and tertiary buds remain inactive unless the primary bud dies or is severely damaged.
Once initiated, shoot growth rapidly reaches its maximum as the climate continues to warm.
It is during this time that the development and enlargement of leaves, tendrils, and inflorescences commences.
As growth continues, the shoot differentiates new leaves and tendrils.
Simultaneously new buds arise in the leaf axils, some of which will form the shoots in the following season.
Those that form early may give rise to what we called lateral shoots.
The rate of shoot growth is greatest just before or soon after flowering.
After flowering, shoot growth decreases as competition for carbohydrates by the developing inflorescence increases.
Shoot development is affected by things like water and nutrient supply, the variety, climate, and vineyard management practises.
Flowers develop as the spring progresses, and during the flowering process self-pollination typically occurs.
If followed by fertilisation, berry development will commence.
At the same time flowering is occurring, inflorescence induction begins in the primary buds and the leaf axils.
For this reason climatic and management factors experienced by the vine during this phase
has significant effects on both the current season and subsequent seasons' reproductive performance, in turn having a big impact on final yield.
Berry development begins through rapid cell division about one week after fertilisation.
It subsequently slows, and may stop within three weeks.
Cell enlargement occurs throughout the growth stages of berry development, but is most noticeable after cell division ceases.
When the berry begins to soften and change in colour this signifies the initiation of the ripening phase, and is referred to as veraison.
At veraison, white grape varieties become translucent and change from shades of yellow-green to yellow
and often golden in colour.
Black grape varieties change from green to various shades of red to purple.
When berry development has reached veraison, primary shoot growth has usually ceased.
The shoots begin to change from green to brown and are then they referred to as canes.
Berry ripening is associated with tissue softening, a decrease in acidity, the accumulation
of sugars, the synthesis of anthocyanins in red grapes, along with the accumulation of aroma compounds.
During berry ripening, seeds change colour from green-yellow to various shades of brown.
Berry ripening can last anywhere between five to eight weeks, depending on the climatic conditions during the period of development.
For viticulturists and winemakers, knowing when to harvest the fruit depends on the variety being grown and the style of wine being produced.
To help assist with harvest decisions we use chemical measures such as pH and sugar level, which we assess during berry ripening.
If harvest is delayed fruit can become overripe, resulting in undesirable fruit characteristics
for a particular wine style.
After harvest, the vine continues the process of photosynthesis, creating carbohydrate reserves to store in the vine's roots and trunk.
It continues doing this until an appropriate level of reserves has been stored.
At that point, the chlorophyll in the leaves begin to break down and the leaves change from green to yellow.
The leaves begin to fall as the vine starts to enter its winter dormancy period.
The following spring the cycle begins again.
You may be wondering what is happening to the root system during development.
The pattern of root growth varies with site, variety, and cultural practise.
At some vineyards, two flushes of growth occur, one early in berry development and the other
after leaf fall.
At other vineyards it may only occur after leaf fall.
To describe the phenological development of the grape vine, we use a system referred to as the Modified E-L system, which identifies major and intermediate grape vine growth
stages.
As part of this course we've developed an interactive E-L stage slider for you to learn more and be able to visualise these developmental stages.
 
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