Ch. 2: The Vine Growth Cycle Flashcards
Flowering
In the vine’s growing cycle, flowering takes place in May-June in the Northern Hemisphere, and November-December in the Southern Hemisphere and is dependent on warm temperatures (>63degrees). The flowers on the inflourescences open and self-pollinate, leading to the formation of seeds and grape berries. Warm temperatures, especially rapidly warming temperatures, are key to successful flowering. Low temperatures can lengthen the flowering time from a few days to weeks or even months, resulting in uneven flowering, fruitset, and ripening. This can reduce quality and grape yield.
Fruitset
The formation of the grape berry, seeds, skin, and pulp after fertilization has occurred. Typically, 30% of flowers become grapes, but this can range from 0 to 60%. Warm temperatures are required for fruitset, with the ideal ranging between 79-90 degrees F. Cold, rainy, and windy conditions can cause irregular fruit set, a key cause of poor yields in cool climates. Hot, dry conditions leading to water stress can also negatively effect fruit set, also causing reduced yields.
Two common forms of irregular fruit set are Coulure and Millerandage
Dormancy
Dormancy occurs in the winter, when temperatures drop below 50 degrees, causing the vine to lose its leaves. Without leaves, it cannot Photosynthesise. The vine survives by storing carbohydrates from the previous season in the roots, trunk and branches.
Grape quality is much higher in vines that go dormant for part of the year. While the vine needs cold temperatures to go dormant, temperatures below -4 degrees F can damage and kill the vine. Meanwhile, if temperatures are too mild, this can cause early bud burst which can lead to uneven ripening and bud damage if freezing weather returns.
Budburst
Budburst occurs in when the sustained, mean temperature rises to 50 degrees, usually in early Spring. Budburst is most successful when the temperatures rise quickly, as in Continental climates. This encourages the buds to burst at the same time which leads to the grapes ripening at the same time. If temperatures are cool in the Spring, this can lead to delayed budburst and uneven ripening, decreasing grape yield and quality.
If temperatures rise in the winter, this can encourage early budburst and increase the risk of damage if freezing weather returns.
Shoot & leaf growth
Begins in March and continues through July, shoot and leaf growth create the green parts of the vine, or the canopy. The canopy includes lateral shoots, tendrils, leaves, and buds, and sometimes, inflorescences.
During this time, the vine needs warm temperatures (>63), sunlight, nutrients, and stored carbohydrates. If carbohydrate levels are too low due to issues such as water stress or fungal infections, shoot growth can be negatively affected. Water stress during this time can also reduce Photosynthesis. Inadequate shoot growth can lead to small weak shoots, a reduction of leaves, inflorescences that do not flower properly, and grapes that do not ripen evenly. This can reduce quality and yields.
Vigour/Vigor
Vigour is a term used to describe the canopy, or vegetative growth on the vine. This includes the leaves, shoots, lateral shoots, and inflorescences.
A vine with high vigor is one with large leaves and long shoots. The vigour depends on many factors, including environmental resources (temperature, sunlight, water), planting material (grape variety, clone, and rootstock), grape varietal, and the presence of disease.
Canopy management techniques are used to control vigour in order to produce the style and quality of the grapes desired.
Bud fruitfulness
Bud fruitfulness refers to the number of inflorescences that will develop from a bud. Increased fruitfulness leads to increased yields.
Buds form in the current season during flowering and fruitset for the upcoming season. During this time, the vine needs warmth (avg. temperatures above 63), sunlight, water and nutrients. All of these factors will affect bud fruitfulness. If any of these factors is inadequate, i.e., water stress, cold/cloudy temperatures, or lack of nutrients, bud fruitfulness, and hence yields, will decrease.
Pollination
Pollination occurs during flowering in May and June when inflorescences open up to form flowers, and the stamen releases pollen into the stigma of the flowers. Grapevines are self-pollinating, and do not require wind or animals to spread the pollen.
Once pollinated, the pollen germinates to develop the grape berry.
Coulure
Coulure is a condition that can happen during flowering and fruit set when there is an imbalance of carbohydrates. This can happen in the Spring if the weather is cold and cloudy, or there is water stress, both of which reduce Photosynthesis. It can also be caused by overly fertile soils and too much vigour, which can divert sugars away from the the grape berries.
Coulure leads to poor fruit set in which a low number of flowers form grape berries, which can reduce yields dramatically.
Millerandage
Millerandage is a condition that can happen during flowering and fruit set in late Spring and early summer in which the grapes do not form seeds. This can happen if the temperatures are too cold and cloudy at this time because pollen germination, and therefore, fruitset, requires warm temperatures, ideally between 70 to 90 F.
Seedless grapes are smaller, and so will produce less volume. Some of the seedless grapes will not ripen at all, reducing grape quality and yield.
Early grape growth
Early grape growth occurs right after fruit set and is the first stage of the ripening process. The grapes at this point are green in color and grow in size. Acids (Tartaric and Malic) and tannins accumulate, and aroma compounds and precursors develop. Water levels are high at this time, and sugars are low.
During this time, slight water stress can encourage ripening by diverting sugars to the grapes and away from shoot and canopy growth. Too much vigour can shads the grapes and lengthen this process, delaying ripening and risking that the grapes won’t ripen fully before harvest.
Aroma precursors
Aroma precursors are compounds that form during ripening which do not appear until the grapes are fermented and/or bottle aged.
Methoxypyrazines
Aroma compounds that cause vegetal aromas and flavors, such as bell peppers, in wine. They accumulate during early ripening, and decrease during ripening. Wine made from grapes that have not fully ripened, or that are picked early in the season, can exhibit these aromas and flavors.
Véraison
Veraison occurs right before the ripening phase, when the grape skins become more supple and change color from green to red or yellow. This is caused by an increase in color compounds called anthocyanides.
Ripening
The ripening phase is the most important vine process in determining final grape quality. During this phase, shoot growth slows, and grape cells expand rapidly. During this time, sugar increases, acids decrease, and tannins ripen and become less astringent. Aroma compounds and precursors continue to develop.
During this time, the vine needs mild water stress to slow canopy growth and direct sugars and nutrients toward the grapes. In addition, sunlight and warmth are needed for sugar accumulation and acid reduction. If the temperature is too hot, sugars can accumulate too quickly, before tannins and aromas fully develop. If it is cool or cloudy, there is a risk that not enough sugar will accumulate, the tannins and aroma components won’t fully ripen, and the grapes will be too acidic.
