WSET Diploma, Week Four – Wine Production: Natural Factors and Human Influences (2)

In Week Three of the WSET Diploma we covered how climate can impact on the suitability of an area for growing certain grapes varieties and how the same grape can produce a very different style if grown in a different climate.
Climate will therefore be an important factor to be considered when choosing a vineyard plot and deciding what grapes to grow which is what we looked at here in Week Four.
Environmental factors such as soil type, slope and aspect will all need to be considered too. Steep hills can provide great conditions for vines in terms of exposure to the sun, air movement and soil type. Soil on slopes tends to be poorer, better drained and more coarsely-textured. Some of the best vineyard plots are on an isolated hill, which means there are no big currents of colder air flowing down from neighbouring hills – think Burgundy’s Aloxe-Corton or Champagne’s Montagne de Reims.

However,  steep hills will increase the risk of soil erosion and increase costs as the vineyard may require a more complex trellising system and harvesting by hand.
Location is key, not only in terms of how easy the site is to access for man and machinery, but how close and accessible it is to the market and local water supplies.
Location can dictate the market potential of a wine, whether a wine produced from the area can attract a premium, which will also impact on the ultimate cost of the land and its affordability.
The location of a vineyard may also determine what regulations will need to be followed. Wine produced in Châteauneuf-du-Pape AOC, for example, will need to have a minimum alcoholic strength of 12.5% (the highest in France), rosé wine production is not permitted, nor machine-harvesting, and yields will be officially restricted to 35hl/ha. Châteauneuf-du-Pape’s chief grape is Grenache but a total of 13 grape varieties can be used, although Château de Beaucastel is one of the few producers to use all 13 permitted grapes. 

Neighbouring vineyards will also be of interest. If a winemaker is looking to adopt organic or biodynamic methods, they’ll want to know whether or not their neighbour is pumping out tons of pesticides.
The political stability if a country is also worth thinking about, the South American wine industry at one time was severely impeded by many years of political and financial instability which restricted investment into wineries.
Many of these same factors will be considered when deciding what grape variety to choose. You’ll also need to think about local styles and indigenous varieties, whether you are looking to be true to the region where the vineyard is located and rediscover local varieties or if you are looking for a more international style.
There are way more factors to consider when selecting a grape variety including hours of sunlight, budget, available skills/expertise, fashion/consumer demand, level of risk 0f early, the need for early/late ripening varieties (this can be important if you are at risk of spring frost or autumn rains), drainage, iron content, drought, vigour, desired yield, winery equipment, style of wine, ready to drink and ageing potential to name but a few.
Viticulture it seems is full of decisions. One of the first for many European winemakers, after selecting the vineyard plot and grape variety is to decide which rootstock to use.
Rootstocks were introduced following the devastation caused by phylloxera in the late 19^th Century. This little louse was accidently introduced from American cuttings in the UK nurseries, spreading like wildfire through Europe and the rest of the world, and effectively wiped out two-thirds of Europe’s vineyards.

While European vines were killed by phylloxera, American vines were resistant and could survive. Only problem was that the American vines often had a distinct foxy flavour to them and couldn’t compete with the quality of European vines, which come from the vine family Vitis Vinifera.
But in 1872, Laliman discovered that European vines could be grafted onto the roots of roots American vines. The result was the best of both worlds, vines which retained their European characteristics and quality but had resistance to phylloxera.
Use of American rootstocks is now widespread, although certain parts of Chile, Champagne and Australia which have maintained their quarantine from phylloxera and the vines there are still planted on their original root systems.
Vitis Rupestris and Vitis Riparia are two American vines which have high resistance to phylloxera. Rupestris is very vigorous and so is suitable for planting in poor soils and can cope with dry conditions. It has, however, a very low tolerance of lime and so vines planted on Rupestris rootstocks are at risk of chlorosis (a vine disorder which turns the leaves of a vine yellow as demonstrated on the right in the picture below, this is due to a lack of chlorophyll and is caused by iron deficiency, which is common in limestone rich soils) when planted on a limestone heavy soil.

Vitis Riparia, on the other hand, is a low vigour vine and is suitable for use in damp conditions and in high density vineyards to help control yield. It encourages early ripening and so is often used in cooler climates. Like Rupestris, Riparia has a low tolerance to lime and so is often combined with another American variety Vitis Berlanderei to create a rootstock which has a high resistance to chlorosis AND phylloxera. Berlanderei is rarely used on its own as it doesn’t root very well and it is difficult to plant. A rootstock made by combining Vitis Riparia x Vitis Berlandieri will have the good rooting ability and resistance to phylloxera of Riparia but with the added value of high resistance to chlorosis.
If you were to mix Berlanderi with Rupestris, you’d get a rootstock with high vigour, good resistance to drought and phylloxera but with a better lime tolerance so it would have a good resistance to chlorosis as well.
The choice of rootstock is almost as important as the choice of grape variety and what rootstock a vine grower choses would depend on the conditions they are confronted with.
If nematodes (microscopic worms that can spread viruses) are a potential problem, one might select a root stock called Schwarzman (Ripera x Rupestris), which is resistant to nematodes and phylloxera, although has low tolerance to lime so could only be used where chlorosis is not an issue.
Vitis Vinifera has a good natural resistance to lime and was combined with Rupestris to create a rootstock called AXR1 which was thought to have some of the lime tolerance of Vinifera but with the tolerance of phylloxera and produces high quality fruit with good yields (high vigour). AXR1 was widely used in California in the 1980s but sadly its resistance to phylloxera proved to be inadequate as California was later hit by a phylloxera outbreak and many vineyards died and had to be dug up and replanted on different rootstocks.
AXR1 used to be widely used in California in the 1980s and was thought to be resistant to phylloxera but this proved not to be the case as California has been badly hit by a phylloxera outbreak and many vineyards have died and need to be dug up.