Thank you Michael Markarian, Darla Hoffmann, and Dustin Chabert for your contributions last week to the discussion on the Appassimento Process!
This week: The Vine Growth Cycle
What is the general required temperature average for vines during the growing season? How does temperature affect the vine and its growth cycle, particularly as temperatures reach extreme levels?
In general, average temperatures around the mid-latitude regions of the continent during the growing season are between 55 and 70 degrees F. Temperatures are critical during this time as typically bud break occurs from March to April, Flowering from April to May, and Fruit set from May to June. Good weather is imperative for ripening, fruit quality, and ultimate sugar and acid levels. Extreme temperatures can mean positive or negative results from region to region. Sunshine and rain will impact sugar and acid levels but depending on the location of each individual vineyard, and what happens in each vineyard during that approximately 170-190 days from bud break to harvest, the end result can be very different. Frosts, early or late, can cause irreversible damage in some vineyards. There are 2 different types of frost. A radiation freeze is when cold air is close to the ground, there are clear skies, and the vines lose radiant heat. An advection freeze is characterized by a moving cold front and cloud cover. There is no air formation and no radiant heat loss. A combination of radiation and advection freeze is obviously most damaging. Some vineyards use wind machines to circulate air from damaging winds, some actually water the vines using sprinklers as a form of protection since the freezing process produces a bit of heat. Using a vine trellising system that keeps the fruit higher from the soils can help control frost. Heaters can be costly but are sometimes used. Heatwaves can be a concern during the growth cycle as well. If the grape skins burn this can be detrimental to ripening. Major chemical reactions are occurring during the growth period which can be halted or altered due to bad weather conditions. Humidity and a lot of rain just before harvest is a problem as the possibility of unwanted Botrytis is a concern. Growers might pay attention to different climate classification systems, such as the Winkler scale, and the Koppen climate classification system to help plan on what varietals will grow best in which regions, and to prepare for certain conditions but these are just averages can never be considered a sure thing. Mother Nature is clearly not always consistent.