September 2011
Photo-finish!
In a year plagued by weird weather world-wide, it may have been easy to overlook the idiosyncrasies of Oregon’s climate this spring and summer. But for Oregon winegrowers, the piper is about to be paid. Normally by the end of September, the grapes will have turned color and be well on their way to full flavored ripeness. Not so this time around. In fact, the growing season started out late, delayed by a particularly cool and rainy spring, and has not really caught up. We are a good 3-4 weeks behind the normal sequence and timing of things. So what?
The process of photosynthesis is a chemical reaction in which water and carbon dioxide combine to form sugars in plants, particularly in their fruit, using energy from the sun. There are several factors that affect photosynthesis, the most important of which are light, temperature and water stress. With the wet spring, and intermittent rains through out the summer, nobody is getting stressed about water, least of all the vines. And winegrowers help the plants out by managing the canopy to assure that the majority of the leaves are exposed to the sun. This is accomplished through shoot positioning, and helped by hedging and leaf removal, so that the leaves are operating at peak efficiency for development of the crop. They get enough light even when it is overcast.
The uncontrollable problem is temperature. Photosynthesis is highest at temperatures between 59 and 86 degrees Fahrenheit. It tapers off dramatically for temperatures above and below those limits. If it gets too hot, the vines begin to respire, which is essentially photosynthesis in reverse, although in addition to sugars, other compounds such as fats, starches and acids may be broken down. If the weather is too cool, which is what we’ve got in Oregon, the whole ripening process takes a lot longer.
This might not be so bad, and the term “hang time” is used by winemakers to denote a period of time beyond when the sugars have reached acceptable levels and during which grapes develop more complex flavors. But the fruit can’t hang around too long without incurring substantial risk of becoming affected by botrytis, aka bunch rot. Rainfall and/or damp weather can bring on the fungal disease, particularly if the skin of the grapes is broken. This can be caused by birds eating the berries, insect damage, mechanical abrasion or even a berry that bursts when the vine takes up water after a rainfall. And once in the vineyard, botrytis is spread quickly from berry to cluster and cluster to cluster, especially if the wet weather continues. Winemakers counter by making sure the fruiting zone permits drying air flow, through the pulling of leaves from this area of the canopy. There are also some sprays that can help inhibit the rot, but the fungi have proven adept at eventually adapting to chemical treatments that are repeated for several years. The real panacea is warm sunshine, and enough to allow the grapes to complete their ripening. This year, there will be a real race to get that finished before the rains set in. Bishop Creek Vineyard, September 30, 2011: The picture shows the fruit zone and clusters with berries which have still not completely turned color.
August 2011 Weighting for Godot
The dog days of summer, like every other weather event this year, are a little late in coming, but they have nevertheless finally arrived in the North Willamette Valley in Oregon. While the ancient Greeks and Romans coined the term dog days to refer a hotter, more sultry period of the summer coinciding with the rise of the dog star Sirius, one modern interpretation infers a period of stagnation or inactivity. This is partly true with respect to the vineyard manager and his crew, who have completed for the moment many of the time consuming tasks of hedging, leaf pulling, shoot positioning and spraying their vines. And now that the initial phase of berry development, which follows fruit set, has occurred, the grape plants themselves do not appear to be undergoing any dramatic transformation. They have already grown from tiny flowers into berries and clusters, and accumulated important acids, minerals and phenolic molecules that contribute greatly to final grape quality. But this apparent calm belies the subtle changes occurring as the berries grow to touch each other, form a tighter cluster and, more importantly reach what is called lag phase.
Approximately 55 days after bloom, depending on the degree days of heat accumulated over the period, generally 1,000-1,300, energy inside the berry is diverted to the development of the seeds. During this phase, which can last 7-40 days depending on grape variety and the temperature, the embryo in the seed matures and the seed hardens. More significantly, the berry has attained roughly half of the final weight it will have at harvest. This means that the winegrower, by taking a methodical and rigorous sampling of cluster weights during this time, can use the information collected to predict the ultimate size of his or her crop. (For those with mathematical inclinations, the formula is average cluster weight, times the average number of clusters per plant times the number of plants TIMES two.) This information is used to decide how much of the crop should, or should not, be thinned to produce the optimal balance between quantity and quality.
Scientific purists will point out that lag phase is really an artificial designation between the two real stages of grape berry development, i.e. the time when the grape switches from berry development to berry ripening. At the end of lag phase, this is also signaled by veraison, a French term which literally translated means the onset of ripening, although it is used to describe the change of color of the berries.
It is dangerous to use the term “normal” when describing weather patterns any more, so rather than saying normally, let’s say that more often than not veraison has occurred by late August each year in the Willamette Valley. But it too seems delayed this year, and so the vineyard manager and winemaker and all concerned with the crop are left to contemplate and weight, er, wait.
July 2011
A Grape By Any Other Name.
After a seemingly interminable spring rainy season, a bit of warmer and sunnier weather in the later part of June and the beginning of July finally coaxed the grape plants in the North Willamette Valley into action. By the 4th of July, many vineyards reported the beginning of the second stage of grape development, i.e. “bloom”. This is the flowering of the grape plant that can occur anywhere between 6 and 13 weeks after bud break. With bud break this year not happening until the middle to end of April, bloom was most welcome when it came and signaled that the plants have caught up a little in their annual life cycle, having started 5-6 weeks later than normal. With bloom in early July, most vineyards seem to be only 3-4 weeks behind now.
Bloom is an extremely important time in the vineyard because if all goes well it raises optimism for a productive year. On the hand, if rainy, cold or windy weather interrupt the self-pollination of the grape flowers, it could make for a poor set, meaning smaller clusters or smaller berries or both and thus less production.
The pollination process in grape plants occurs when the individual grape flowers open by shedding their cap, called the calyptra. As the cap falls away, sometimes called shatter, the stamens are exposed and pollen is released. A grape plant is hermaphroditic and so the pollen usually falls on the plants own pistils, the female part of the plant, and germinates by penetrating the style and ovary of the pistil. If it is rainy or windy, the pollen may be blown or washed away before it completes its job. Cold weather is also problematic because the ovaries literally close up, making germination more difficult.
Although the green flowers of the grape are not very noteworthy as flowers go, the plant does release a pungent odor from the base of the pistil during bloom which is supposed to be an aphrodisiac. And although it may not rival the sweetness of Shakespeare’s rose, to a winegrower that aroma of fruit flowering is pretty exciting.
May 2011
Waiting for Godot, er, GDD.
The extended period of rainy weather this spring has been lost on no one who has bothered to poke their head outside. The effect of this on local grape vines has been to significantly delay, by 3-4 weeks, the normal occurrence of bud break, that point in time when the new green shoots of a grapevine finally emerge (burst or break) from the buds on the cane. With this late start, what’s the effect going to be on the eventual wine grape crop?
This depends on a number of factors that will develop between now and harvest, the most important of which is the accumulation of something called degree days or growing degree days (GDD). It is widely assumed that grape plants are not actively growing unless temperatures reach at least 50 degrees Fahrenheit. A number of horticulturalists have posited variations of the theory that wine grapes must accumulate a certain amount of heat in order to ripen. They measure the accumulated heat by taking the daily mean temperature (the maximum for the day plus the minimum divided by 2) and subtracting 50. This gives one the number of growing degrees the plant has accumulated each day, which when multiplied by the number of days, yields the result, the GDD. Wine grape plants need somewhere around 1,500-1,700 GDD to ripen. So the main factor this year will be whether we can accumulate enough degree days before the weather turns cold again in the fall.
But like almost everything related to grape growing, it is just not that simple. Other research has shown that grape plants stop growing when temperatures get too high. They respire, which is more or less the opposite of photosynthesis. This inhibits the normal ripening process. As a result, if we have a number of days where temperatures are extremely high, above 90 or so, then that heat is not really making up for the slow start in the spring. Sunlight is another factor. There are a number of areas which are warm enough to produce quality wine grapes, for example east coastal Australia, but which do not because of cloud cover. Thus although there are an adequate number of degree days during the growing season, the photosynthesis occurring in the plant is affected and that results in lesser quality fruit. Naturally, rainfall also plays its part as common sense suggests that no plant does well unless it receives the right amount of moisture.
So, with all those factors still unknown for this growing season, it becomes less of an existential practice and more speculative to forecast the eventual merits of the vintage. But what one is left with is a better appreciation of why the growing of grapes is so complex and, as a result, so intriguing in its variety.
