After the grapevines awake from their winter dormancy, the plants go through five major phases during their growing season. The quality and quantity of the fruit at harvest are greatly affected by the weather events and daily temperatures that occur during these important growing stages.

During this first stage, the grapevine plants begin to show signs of life after a long winter slumber. Driven by rising air and soil temperatures, tiny, fuzzy buds begin to emerge from the woody plant stalks. The plants won’t begin to awaken until daytime temperatures rise above 50˚F/10˚C for a sustained period of time. However, if nighttime temperatures dip below freezing (32˚F/0˚C) during this process, the fragile new leaves can be damaged. A major frost event can even kill the new growth– which is a truly heartbreaking way to end a vintage just as it was beginning.

To read more about bud break, follow this link to our Viticulture 101: Bud break in the vineyard article.

Before the grapevines can produce grapes, they must first grow flowers. These blossoms are really just tiny grapes in the making. While bloom is the initial sequence in this cycle, it is closely followed by flower and fruit set. During any given vintage, less than half of the grapevine blooms will actually grow up to become grapes. Weather events such as heavy rain, wind or a late frost can damage the delicate flowers and dramatically affect the final number of grape berries within each cluster. Fewer berries mean less fruit and smaller yields, resulting in less wine that particular vintage. Sometimes flowers blossom at slightly different times, creating a situation where berries grow at different rates on a single grape cluster, some larger and others smaller. Referred to by grape growers and winemakers as hens and chicks, this isn’t always such a bad outcome and can contribute to better cluster ripening and reduce the possibility of mold since air can flow between the berries.

Click here to read our Viticulture 101: Grape bloom, flowering and fruit set in the vineyard post.

During the ripening phase, grapes love nothing more than plenty of sunshine and warm weather. Cooler temperatures and rain can increase disease pressure and heighten concerns about mildew. Conversely, really hot daytime temperatures can speed up the ripening process. Did you know that grapes can get sunburned?

Too hot or too cool… neither of these situations are ideal for wine grape growers. Fortunately, they can utilize vineyard techniques such as leaf-pulling or leaving a fuller canopy to help mitigate the effects of some undesirable conditions. While the grapes are ripening, slow and steady (weather) wins the race.

Pronounced ver-AY-zhun, véraison is a French word that describes the period when grapes color change (red varietals) and begin their final ripening. This is the final growing phase before harvest. It’s important to note that véraison marks the end of acid accumulation in the wine grapes– as if a switch is flipped in each grapevine. Before véraison, the grapes build up acid levels and once véraison is over, the grapes concentrate on storing sugar, using their acid reserves for energy to get them through the rest of the summer until harvest. It’s similar to how a bear builds and stores fat for a long winter hibernation. Véraison is the last stage before harvest and occurs roughly 40-50 days before the grapes are fully ripe and ready to harvest.

Check out our Viticulture 101: Véraison in the vineyard post to learn more about the subject.

Grape growers and winemakers evaluate many factors when making their picking decisions. They’ve only got one chance to do this each year! The most important harvest decision is based on the French term known as brix. It refers to the grape sugar levels– which will eventually convert to alcohol during the winemaking process. To measure brix levels while out in the vineyard, winemakers crush a single grape, then add the juice to a device called a refractometer. When held up to the light, a small gauge that measures the sugar level is visible through the eyepiece. Knowing the grapes’ sugar content is vital. If you pick grapes with higher brix levels, your wine will have a higher percentage of alcohol. While higher alcohol wines might get people drunk faster, they don’t pair as well with food.

Weather events such as rain or an expected frost can force a grape grower’s hand, requiring them to pick the grapes sooner or later than desired. A prime example of how disruptive rain can be was during the 2013 Oregon harvest, when the remnants of a typhoon soaked many parts of the state. It set precipitation records over much of Western Oregon, including in the Willamette Valley town of McMinnville, where over 7.5 inches/19.05 centimeters fell over the last weekend in September!

Click here to read more about how this deluge affected the 2013 harvest.

Wildfire smoke is another concern that is becoming more common as our climate changes. Smoke clings to and can permeate wine grape skins, but no one knows exactly what exposure level is enough to cause smoke taint. The other problem is that smoke aroma and flavor don’t become apparent until after fermentation. Most Oregon winemakers experienced this dilemma during the 2020 harvest. With testing labs backlogged for weeks, winemakers across the state had to make tough choices about whether or not to pick fruit, all without complete information from the lab about just how much smoke the grapes might have absorbed.

Follow this link to read more about smoke taint.

Labor shortages can also complicate the harvest process. Pickers might not be available on the exact day a grape grower wants their fruit snipped from the vines. The COVID-19 pandemic is certainly not something anyone had to consider in the past either. Social distancing is easy when the pickers are working in the narrow rows but becomes more challenging when they hustle past one another with their buckets of fruit.

Depending on the timing of harvest, hungry birds and bears must be considered as well. Spring of 2010 in Oregon’s Willamette Valley was cold and wet, causing the grapevines to slumber longer than usual. This delay resulted in ravenous bears and birds in search of food as the grape harvest neared. While there are ways to deter starving animals, nothing is foolproof. That year, referred to as “the year of the birds,” many vineyards in the Willamette Valley lost some– if not most– of their grapes to the animals.