What Is This Weather Doing to the Pinot Noir?

Pinot Noir lovers often ask Willamette Valley Winemakers, "What is this weather doing to the wine?" usually in response to weather events at the extremes of the normal range.

This post breaks down the growing season into three periods; budbreak to bloom, bloom to veraison, and veraison to harvest, discussing how weather events during these periods might impact your favorite Chardonnay or Pinot Noir.

Budbreak to Bloom

Though considerable work is done in the vineyard during the vine's dormant period, the growing season begins at Budbreak when the urgency and volume of vineyard activities increase.

The vine does not yet have grapes during this period, only their embryonic precursors. Because of this, weather incidents during this period have little direct impact on the wines of the vintage. However, as we will discuss below, extreme weather events at this time can have indirect effects on the season's wines.

Hot weather during this period will have little direct effect on the wines. Depending on the producer and Style of wine, the harvest commences between 90 and 110 days after bloom. Warm weather after budbreak will accelerate the onset of bloom and set the timeline for the harvest window.

More dire and troublesome during this period are cold and wet weather conditions. After budbreak, the vine becomes highly susceptible to frost events. Frost can wreak havoc on yields. In addition, the destruction of the primary buds can lead to the development of secondary buds. In a vineyard where both primary and secondary buds are maturing, there can be a greater than usual diversity in the grape's physiological development, making assessing ripeness and pick dates difficult.

Hail is another devastating weather event that sometimes happens during this period. The falling ice can damage leaves, clusters, and the woody parts of the vine. This damage can reduce yields and the capacity of the vine to ripen its crop.

Cool and wet weather can also reduce the success of bloom resulting in fewer berries per cluster and lower yields in general.  Yields outside of an optimal range, either low or high, can impact wine quality depending on the weather events during later developmental periods, disrupting the critical balance between sugar accumulation, acid respiration, phenolic extractability, and flavor development.

“Though vineyard managers, viticulturists, and vineyard workers have already been hard at work for weeks, bloom marks the beginning of the growing season for winemakers”

Bloom to Veraison

Though vineyard managers, viticulturists, and vineyard workers have already been hard at work for weeks, bloom marks the beginning of the growing season for winemakers. It is generally accepted that it takes 500-degree days to induce flowering in Pinot Noir.

"Growing Degree Days (GDD) are used to estimate the growth and development of plants and insects during the growing season. The basic concept is that development will only occur if the temperature exceeds some minimum development threshold, or base temperature. For winegrapes, that threshold is generally considered 10°C (50°F), below which the vine's metabolic activity is reduced dramatically.

Hot temperatures during the early part of this period will have little influence on the sugar and acid profiles of the harvested fruit. However, as veraison approaches, warmer temperatures may increase the carbohydrate in the vine, which may quicken the loading of sugar in the grape berry after veraison, but not dramatically so.

During hot temperatures exceeding 40°C (104°F), the vines "shutdown" and become much less photosynthetically active. This shutting down can, counterintuitively, slow the physiological process of ripening. The developing grape berries are also susceptible to sunburn at this time, and high temperatures can damage the skin of the berries. Such damage can impart off flavors, result in course tannins and reduce yields due to either aborted berries or the removal of affected clusters. Sunburn results in considerably more work for winemakers.

During this period, the vine's canopies become dense and filled in as leaves develop and lateral shoots emerge. Such density reduces airflow and light penetration. Humidity during this period can result in ideal conditions for fungal growth, affecting both the leaves and berries. The negative consequences of this increase in "disease pressure" can appear now or later in the next period.

Cool and wet weather at the beginning of this period can increase the likelihood of botrytis infection at harvest.

This phase of grape development is when the berry synthesizes tannins. This production is in response to the grape skin's exposure to sunlight. Though studies largely attribute this synthesis as a response to light independent of temperature, it is clear that weather that favors bright sunlight can influence the structure of a vintage's wines.

Weather extremes from bloom to veraison can influence the character of a vintage's wines. However, the most impact will be related to disease pressure and structural, i.e., tannin development. The degree to which weather impacts harvested fruit's sugar and acid profiles increases dramatically after veraison.

Veraison to Harvest

Veraison marks a change in the vine's physiology in preparation for maturing the vine's reproductive organ, the grape. The grape begins to change color as pigments, also known as anthocyanins, start accumulating in the grape’s skins. The berries begin to soften. The skins become more pliant. Sugar begins to accumulate in the berry rapidly, and acids decrease. These changes increase the fruit's susceptibility to environmental conditions.

The adage "the wine is made in September" reflects how the weather in this period shapes a vintage's quality and character. However, this assertion is misleading. In the past, harvest, unless hastened in response to rain, was primarily an October affair.  September isn't magically the month that shapes the wine but has historically been the last three to six weeks of the grape reproductive cycle when it is most susceptible to being shaped by weather conditions.

Climate change, specifically through warmer winters and springs, is resulting in earlier bloom periods than was typical of the past. Early bloom leads to early veraison (though not perfectly so), which shifts the grapes increased susceptibility to earlier in the season. Harvest windows in September and even August are more likely to be warm and hot. Thus weather in the previous developmental periods can influence the vintage indirectly.

Hot temperatures and clear days during this period increase the sugar loaded into the berry. Dehydration which the now soft and plaint berry is more susceptible to, can further exacerbate the rise in sugar. If excessive, the dehydration can result in "dimpling" or "raisining" of the grape, which can result in flavors described as "dried", "pruney", or "stewed"." Winemakers, especially those in the Willamette Valley, deeply appreciate the magic of moderate weather in the last few weeks of ripening.

Temperatures also influence acid levels. However, what matters most isn't daytime temperatures but those at night. Winemakers working with Chardonnay and Pinot Noir dread cloud cover at night as it generally means warmer temperatures. These warmer evenings result in respiration and, thus, lowering Malic Acid levels, increasing the pH.

Summary

The next time you see a weather report for your favorite wine region, the Willamette Valley, and wonder how it will affect the vintage's Chardonnay or Pinot Noir, remember these general rules:

·      High temperatures before bloom accelerate flowering and have little impact on the vintage's wines but set the stage for the harvest window about 100 days later.

·      High Temperatures between Bloom and Veraison might slightly affect berry sugar and acid profiles at harvest. They may also contribute to increased levels of tannin though the degree of sunlight striking the berry is the most critical factor.

·      Temperatures between veraison and harvest profoundly impact the vintage wines, with the final three to four weeks of the season "shaping" the vintage.