Tuesday, 22 May 2012 19:02

Viticulture

 Viticulture Basics: Viticultural practices in the vineyards have direct influence on the type and style of wine that can be produced from any area.Grape vines are basically weeds.  They’ll grow anywhere with a bit of sunlight and little water, let alone any pruning. 

They're resilient, persistent and can survive in most places without a lot of care or attention - much the same as any other weed. However, before the viticulturalists reach for their bug spray to silence me, remember there's a lot more to viticulture than you need to understand for the purpose of choosing or enjoying a great wine. What we'll discuss here is just the basics. Table grapes can grow in most places quite successfully. However, not everywhere is suitable for growing wine grapes.

Wine grapes require a balanced combination of colour, acidity and sugar, so they don't make the best wines when exposed to temperature extremes. Too much cold = too much acid, and too much heat = too much sugar. Table grapes on the other hand are not so discerning - the more heat, the more sugar for them. There are specific regions in the northern and southern hemispheres where the weather and climate are favourable for growing wine grapes. The bands on the map below show generally where these optimum wine grape growing regions are on the globe. 

In the northern hemisphere, the best regions lie between latitude 30º and latitude 50º [around Tunisia to Germany]. In the southern hemisphere, between latitude 23º to 45º [half-way down Australia to New Zealand]. Within these quite defined climate bands there are optimum levels of sunlight, temperature, rainfall and humidity required to develop desirable sugar and acid levels in wine grapes to make particular styles of wine.

When wine grapes check in, they come with a hefty rider:

  • Avg temp coldest month must be greater than -1ºC

  • Avg temp warmest month must be greater than 17ºC

  • Lowest temp in any 20 year period must not drop below -20ºC more than once

  • More than 180 frost-free days:
  • Minimum 1200 hours sunshine during the growing season

  • Rainfall greater than 450mm annually [750mm in hotter regions] … although irrigation can make up shortfalls

... and this is just for starters. There are many more technical specifications determined by the type of grape grown. As the sun travels along the line of the equator, there is too much light and heat in the areas between the optimum climate bands to grow fine wine grapes. Best leave those areas for sugar cane and rum distilleries.

The sun's equatorial path also has a bearing on vineyard sites situated on hillsides. To make the most of available sunlight in the optimum regions the correct aspect has to be considered: southern hillsides in the northern hemisphere, and northern hillsides in the southern hemisphere - particularly in cooler areas.

Different grapes, and the different wine styles or types that can be made from them, need specific climatic elements to succeed. Old Worldviticulturalists go even further, referring to the terroir of a wine region when they characterise its suitability for particular grape varietals. There is no doubt that individual locations for vineyards have a great bearing on the grape varietal most suited to growing conditions available, and on the style of wines that can be made from the grapes.

Different macroclimates have varying rainfall and sunlight hours.  As mentioned above, heat = sugar. Thus grapes which receive lots of sunny days in which to ripen will have higher sugar levels, and grapes which receive too much water will bloat and have less flavour. The lay of the land also has an effect on grape choice. In Colmar [Alsace region, France/Germany border] Riesling grapes ripen well. However a mere 40 km to the west in Freiburg in the Baden region of Germany, they won't ripen! Why is this so? Colmar is [slightly] warmer and has less rainfall due to its being in the rainshadow of the Vosges Mountains.

There are many location-specific climatic influences that affect wine style.

For example, take Shiraz grapes grown in higher temperature regions ... The enzymes which produce anthocyanins [responsible for colour] in the skin of the grapes work less effectively over 26 degrees celsius. Thus hot climate Shiraz has much less colour. Sugar levels on the other hand will be higher [as long as it doesn't get too hot for transpiration]. The resulting wine style will likely be medium to full-bodied, with low to medium colour intensity.

Let's consider Australia, where higher sugar levels attained in the Rutherglen region of north-east Victoria enable heavy bodied fortifieds [Port, Muscat, etc] to excel from red grapes. On the other hand, Tasmania's chilly seasons encourage higher levels of acidity in white grapes required for fine, dry sparklings, but lack enough warm days to ripen Shiraz with adequate sugar levels or skin colour to make medium-full bodied wine.

But there’s more … subtle differences between mesoclimates within a region will have varying effects on the varietals, and the style of wines which can be made from the ripe grapes.  This is one reason that all wines don't taste the same.

So, if wine grapes are grown outside the optimum climate bands, does this mean they’ll make undrinkable wine?  Short answer – not necessarily. 

Long answer – certain mesoclimates can create area pockets outside of the optimum climate band regions which have suitable temperatures and number of sunlight hours for the grapes to flourish. Then there's canopy management which also facilitates successful winemaking from grapes improving the microclimate of the vine canopy. This is where the viticulturalist really earns his money - by maximising the available climatic conditions to encourage berry flavour development and ripening.

To do this, the vines are grown to shapes that allow sunlight to easily reach the leaves and fruit. Trellising serves initially as a support for young vines to shape, and later as support for the mature vines. Exactly what form this trellis takes is determined by the expected vigour of the vine. It's common to see European vineyards using single poles to train vines. Sometimes they use nothing at all and train the vines as bushes. Modern viticulture, prominent in the New World wine regions, on the other hand, uses quite elaborate structures to train vines.

Apart from canopy management reasons, New World wineries also tend to use more mechanical pruning and harvesting - which most trellising readily enables. A more important factor for mechanical operations though is the spacing between the vines - which can be anything from 2.5m to 4m apart. This wide spacing allows maximum sunlight to reach the grapes as the rows don't overshadow each other.

Old World vineyards are much older, often on steep slopes and have been pruned by hand for centuries. In many cases, their rows are much closer together - as little as 1m apart.  Source: Cellar Door to Door, as of 2011.

More in this category: « Terroir

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