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.
