The science of viticulture: Climate and site selection

Quality grapes are a precursor of quality wine and the science of viticulture has developed and evolved with a single goal in mind: the delivery of high-quality wine grapes to the winery.  The quality of wine grapes produced in a specific harvest is not only a function of that year's harvest conditions.  Rather, it is the result of a combination of factors which, together, represent the full scope of viticultural science.  I will cover most of the inherent elements of viticultural science in a series of posts as a part of my investigation of the source of grape-derived odors.

There are three major areas of concern for the viticulturist as he/she sets about the task of delivering quality grapes to the winery door: (i) selecting the site which will best ensure goal attainment; (ii) setting up the vineyard with the appropriate elements such that cost-effective goal-attainment is promoted; and (iii) implementing a cost-effective, repeatable vineyard management regime which is reflective of the operating conditions.  Within these major considerations there are a number of sub-elements where the rubber really meets the road and I will focus our coverage of the topic on these areas beginning with today's writeup on climatic considerations in site selection.

The site selected for a new vineyard will determine the amount and quality of fruit produced, the resources required to manage the vineyard, and, ultimately, the profitability of the vineyard.  Selecting a site for a new vineyard is generally a compromise between a number of factors.  For example, most of the exceptional vineyard sites in the world have been under vine for many a year, leaving less-than-perfect options available for the aspiring vineyard owner.  Second, most prospective vineyard owners are drawn to sites that are readily accessible to them and this limiting facor comes with a given climate.  And so on.  Site selection is thus the process of making an optimal choice within the bounds provided bythe needs of the wine grapes, the available site options, and associated limiting factors. 

Source: Compiled from arcserver2.iagt.org

The key site-selection factors for consideration are climate and site physical characteristics.  Climate, according to Dr. Tony Wolff (Lecturer and Viticulturist, Virginia Tech) and John D. Boyer, is the average course of weather in a region over an extended period as measured by temperature, precipitation, and wind speed, among other variables (Vineyard Site Selection, Virginia Cooperative Extension).  Weather is itself defined as the state of the atmosphere at a specific point in time using the same variables as referenced in the climate definition above.  The climate of a grape-growing region will determine, to a large extent -- and all things being equal -- both the grape varieties that can be grown and the styles of wine that can be produced.  For example, Syrah appears to flourish in warm climates while Riesling does best in cold.  That is not to say that these varieties cannot be grown outside of these environments; that is to say, however, that varietal typicity is compromised when these varieties are grown outside of their "zones."

As it relates to the wine regions of the world, the ideal climates for vitis vinifera are Mediterranean and marine west-coast climates which are both characterized by mild, wet winters and warm, dry summers.  The mild winters promote long-term survivability of the vines (and increased quality of the juice as the vines age) and the wetness provides a reservoir of water that the vine roots can tap into during the grape maturation cycle.  The warm, dry summers provide the heat and light that are the engines of vegetative and crop growth while keeping at bay the threat of rot and flavor dilution that would accompany summer/fall rains.

Source:www.buywineonline.co.uk

In viticulture, three separate aspects of climate are normally considered: macro-climate, meso-climate, and micro-climate.  Macro-climate refers to climatic effects over large (hundreds to thousands of miles) geographic areas and are either continental or the aforementioned maritime.  Continental climates are modified by large land masses and are characterized by hot summers and cold winters.  Maritime climates, on the other hand, are modified by proximate large bodies of water which heat up and cool down at a slower rate than does the adjoining land mass.  This scientific fact results in the warming of winter winds as they blow over a warmer body of water and the warming of landside vineyards as the winds make landfall.  This warming could act to extend the growing season and minimize the potential vine impact of winter low-temperature events. On the other side of the coin, warm spring air blowing in over the still-cold water will be cooled down and will retard the development of landside vineyards, minimizing their potential for damage from spring frosts.

Meso-climate covers a much smaller area than does macro-climate and is generally the scale at which site decisions are made.  It is at this level that that the physical aspects of the surroundings -- elevation, slope, aspect -- can temper broader macro-climatic effects.  The climatic effects of these physical elements will be covered when they are discussed individually.

Micro-climate are the conditions that exist in the vineyard from the soil upward into the vine canopy and, as such, is more relevant when the land is under vine than in the site-selection phase.

One of the key grape needs is adequate sunlight and heat to allow both the fruit and the vegetative aspects of the plant to mature.  The progression of the grape through its various stages of maturity is influenced by the ambient temperature with research indicating that growth of the grapevine begins when temperature exceeds 10℃.  A measure -- growing degree days (GDD) -- has been developed to measure the accumulation of heat (as measured by temperature) in excess of 10℃ over a growing season.  Extensive research has yielded the following GDD parameters which can be used as input in the site-selection dialogue.

Source: Compiled from oregonviticulture.net

These then are the broader climatic considerations for the viticulturist in selecting a site for a new vineyard for the production of quality wine grapes.  The physical characteristics that should be evaluated will be covered in the next post on viticultural science.


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