Cards of Wine

The Life Cycle of a Grape

The grapevine (Vitis vinifera) is the most widely cultivated and economically important fruit crop in the world.

Wild grapevine seeds naturally germinate in humid and shady riverbank forests.

Domesticated grapevines are called cultivar (cultivated varieties). They are propagated from cuttings, not grown from seeds and selected via hybrids and clones. A couple of years after planting, they start to produce fruit, every year and for many decades. The lifespan can be over 100 years.

Winter Dormancy

December - February (Northern Hemisphere), July - September (Southern Hemisphere).

The drop in temperatures triggers the dormancy stage. Nutrients (carbohydrates) are stored (cordon, trunk, roots) and the vine loses water (dehydration) to not freeze and avoid winter frost damages.

Dormancy is the stage with no growth activity: from autumn (leaf fall) to spring (bud burst). The vine rests.

Winter pruning

Pruning is a selective removal of fruiting branches and buds (70-90 %) to assure energy and nutrients to fully ripen grapes.

Thye big secret is that fruit is produced only on shoots from one year old branches so the goal is to maximize their amount. Too much vegetation could result in lack of nutrients, excessive shading, high crop load, uneven ripening or encourage diseases.

Bud Break (Budding - Budburst)

March -April (Northern Hemisphere), September - October (Southern Hemisphere)

Bud break begins when daily temperatures reach 10 °C (50 °F).

As temperature and light intensity increase in early spring, stored starch is converted into sugar, and sap begins to move in the vine (bleed). Buds swell and burst generating new shoots.

Budding is the first sign of life. The vine is weaking up and needs to produce leaves to generate carbohydrates via photosynthesis to fuel the new growth. The vegetative activity accelerates and branches grow 5-15 cm a day.

Buds are delicate and vulnerable to frost and hailstorm.

Cluster inflorescences appears opposite 3rd and 4th leaves on a shoot.

Flowering

April-May (Northern Hemisphere), October - November (Southern Hemisphere).

The flowering period can last one or two days in a warm, dry climate, or one month in a cool, wet climate.

Flowering depends on the warmer temperature and stronger sunlight: a daily temperature of 15-20 °C (59–68 °F) activates the process.

Grapevine flowers bloom in a cluster 6 to 9 weeks after bud break.

Domesticated Vitis Vinifera varietals are hermaphroditic: the blossoms self-pollinate, without help from bees, because flowers are bisexual (have both sexes). Pollen from a male flower (stamen) fertilizes the female flower (ovary), and a seed (embryo) develops. The entire ovary grows to become the grape berry itself with seeds contained within.

Flowers are delicate and vulnerable to harsh wind, cold and heavy rain.

Fruit Set

May - June (Northern Hemisphere), November - December (Southern Hemisphere).

As temperature rises, the growth accelerates, shoots expand and the vine starts to produce new nutrients (photosynthesis).

Through cell division and expansion, berries grow. They are green and hard, high in acid and low in sugar.

Canopy Management

Canopy refers to leaves, shoots and fruit.

Canopy management means to design the architecture of a grapevine and guide its energy into the ultimate result: perfectly mature fruit.

It involves pruning, shoot positioning, thinning, foliage removal, trellissing (fastening branches to iron wire to maintain an upright direction), etc.

Canopy management optimizes the yield, improves fruit quality, reduces risk of disease, improves sunlight exposure, reduces shading, etc.

Through Canopy Management the energy is used less on producing leaves and more on ripening fruit (optimization).

Crop Thinning (Green Harvest)

Crop thinning means to cut bunches to limit yields so the nutrients go only to the remaining bunches. This assures higher quality wine through removing part of the vegetative growth, it supports the fruit vigor and selects the best quality grapes.

In cool climates it helps the fruit to ripen (clear shade).

Veraison (Berry Ripening)

July - August (Northern Hemisphere), January - February (Southern Hemisphere).

Veraison is the stage where the grapes begin to change color (30-70 days after fruit set). This is a signal of fruit maturation (ripening), berries begin to soften, acid level falls and sugar level rises.

The balance between sugars and acids is the most critical aspect to determine the quality of the wine. The longer the grape is on the vine, the higher the sugar and the lower the acidity will be.

All grapes start out green. Then they turn yellow (white grapes) or pink, red, purple and black (red grapes).

Veraison is uneven (different degrees of ripeness) and the berries exposed to more sun and light get a head start.

Harvest

August - October (Northern Hemisphere), February - April (Southern Hemisphere).

The enologist chooses when to harvest (45 days after mid-Veraison, 120 days after flowering). The main factors are: phenolic maturity (skin thickness, berry texture, seed and stem color: green to brown), optimal sugar, pH and acidity levels, optimal ripeness, wine style, weather forecasts, man power, etc. Generally it takes from one week to a month of hard labor. Once you start, you can't stop.

White grapes mature sooner, so they are the first harvested, unless you want to make a late-harvest, noble rot sweet wine style.

Black grapes need more time to achieve the ideal color, and sugar-acid balance.

The date of harvest is rarely the same: pick too early and the tannins result green and bitter, or pick too late and sugar levels go too high killing the acidity (flabby wine). Sparkling wines need high acidity therefore the harvest is early.

The enemy at this stage is the fungal infection Botrytis that causes grapes to rot under rain-induced humidity.

Hand-picked grapes have better quality because grapes are delicate and break easily during machine harvesting (since 1960s). A broken grape skin results in premature start of fermentation.

Crushing vs Pressing

Grape clusters are first sorted (Triage) for quality (unripe, diseased, damaged grapes, leaves, bugs), then destemmed, crushed, and pressed.

Crushing (Foulage) means to break open the skins by gentle pressure so the pulp (juice) gets access to yeast, tannins and broken skins. These solids provide body, color and flavor to the juice. Crushing is used to make red or rosé wines. Modern destemmer/crushing machines are calibrated to not to crush the seeds which are full of bitter tannins.

Crushing is different from Pressing (Pressurage) where the grapes, clusters and pomace are pressed to extract the juice (no skin or tannin contact). Pressing is used to make white wine (no skin contact). Pressing in red wine production happens after the alcoholic fermentation.

Fermentation

Alcoholic Fermentation is sugar + yeast transformed into alcohol + CO2.

The brewing and baking yeast Saccharomyces cerevisiae, ferments grape juice (must) into wine.

The main difference between white and red wines is that white grapes are first pressed and so fermented. Red grapes are first fermented, so placed in vats to macerate and finally pressed.

After alcoholic fermentation you can choose to start a secondary fermentation called Malolactic where Malic Acid is converted into Lactic Acid by Oenococcs Oeni bacteria.

Aging (Élevage)

Sulphiting (to add sulphur) protects the wine by preventing microbial growth. Sulphur is added before the long rest (several months) called maturing or aging (Élevage). Since sulfites form naturally during fermentation, nearly all wines contain low levels of them even when not added up or sprayed in the fields.

Aging in steel or oak barrels? How long? How much to manipulate it? Wine can be stored in oak barrels between 8-24 months. This period depends on the vintage and style of wine. Exchange of aromas from the oak barrels and oxigen (micro-oxigenation) takes place. The portion of spirit lost to evaporation is called Angel's Share and barrels must be topped off regularly.

Bottling