WSET Diploma, Week Three – Wine Production: Natural Factors and Human Influences (1)

Apologies – I’ve got  little behind with documenting my WSET Diploma wine studies but document I will, better late than never!
The next two viticulture classes were taken by Anna Martens, an Australian who has spent time as a flying winemaker in South America and Italy and is currently working on a project called Vino di Anna on the volcanic soils of Mount Etna.
First we looked at the vine in nature, where it is a creeping, climbing plant that is part of a polyculture, i.e. it co-exists alongside many other plants and animals. When a vine is cultivated for wine production, the vine is pruned which can weaken the vine as prune cuts may leave it susceptible to fungal infections and diseases. A vineyard, which is planted solely with vines, creates a mono-culture and a situation which is more susceptible to plants and diseases due to lack of biodiversity.
We recapped on the environmental conditions needed to grow and produce grapes – sunlight for photosynthesis (circa 1500 hours of sunlight on average), water (500-700 mm), CO2 and warmth (the vine is dormant at temperatures under 10°C).
And then the regional climate classifications, which divides wine making regions into cool, moderate, warm and hot based on the temperature during the growing season which is April-October in the Northern Hemisphere (October to April in the Southern Hemisphere) 
Cool climates have a mean average temperature of less than 16°C during the growing season and include the likes of Southern England, Champagne and the Mosel Valley, Germany. Because of the cooler climates early ripening varieties such as Riesling are often favoured.
Moderate climates are designated as having a mean temperature of between 16.5° and 18.5°C and includes famous wine making regions like Burgundy, Tuscany, Northern Rhône and Rioja, grape varieties like Cabernet Sauvignon, Merlot, Syrah and Sangiovese do well here.
The temperate range for a warm climate is 18.5° and 21°C, which you’ll find in South Africa’s Stellenbosch or Sardinia – late ripening varieties such as Grenache, Mouvedre and Cinsault will enjoy these warmer climes.
Hot is anything above 21°C and includes Central Valley California, which is thought too hot for fine wine production. Grapes produces in such hot conditions may well be destined for life as table grapes not wine grapes.
The relative level of temperature is not the only marker for regional climate classification, the degree of continentality is also considered, that is the difference between the warmest and the coolest month. A maritime climate will enjoy warm sunny summers, mild winters with most of the rain occurring during the Autumn, like in Galicia.
Mediterraean climates have the same warm sunny summers and mild winters but most of the rain will happen after the growing season in winter (e.g. Chile).
Continental climates see a big difference between the hottest month and the coldest month so have warm or hot summers and cold winters and most of the rain falling during winter. The Loire, Champagne and Rioja are good examples of this.
Tropical climates have no distinct seasons, aside from possibly a rainy season. With no winter, the vine therefore doesn’t know when to rest and so there may be two harvests a year. Examples: India, Brazil and Mexico.
Why does all this matter?? Well, a wine from a cool climate can have a very different flavour profile to a wine made from the same grape variety grown in a moderate or warm climate. Certain grapes are most suited to cool or moderate climates, Riesling, Pinot Noir being two examples, while others such at Chardonnay are at home in a range of different climates but produce a very different style of wine in a warm climate than in a cool climate.
As an example we were given two wine to try, both were said to be from the same grape variety but one was grown in a cool climate and the other in a warm climate.
Once again, we were tasting these wines blind, the first was a deep purple colour with aromas of ripe dark, verging on baked fruit – blackberry and plenty of oak and spice,  On the palate it was full-bodied, gave a little warmth on the back of the throat suggesting high levels of alcohol and had bags of ripe black fruit and chewy tannins.
The second wine was medium plus in colour(the dark side of medium), again with concentrated fruit, blackberry and a little vanilla. On the palate, it had less body and alcohol than the first and quite drying tannins.
The first wine was a warm climate, Barossa Valley Shiraz at 14.5% and the second a cooler climate Hawkes Bay Syrah from New Zealand.
The deep colour of both of the wines pointed to a thick-skinned variety and the relative ripeness and alcohol levels helped to identify which was the warmer climate wine.
Various classification systems have been created to help determine what varieties are most suited to which area.
One of these is the Heat Summation system created by Amerine and Winker (1944) who found that the quality of the wines produced in California reflected the heat summation of the sites on which they were produced.
To calculate, you take the mean average temperature for each month, minus by 10 (as below 10°C the vine is dormant) and times by the number of days in the month. The monthly sums are totalled for each of the seven months of the growing season.
Now this table is just one of those you need to memorise for the exam. Category I is below 1370 degree days and will be most suitable for a light-bodied white wine, over 2200 and a grape is destined for a bulk wine or table grape.

The EU has its own regional climate classification and zones have a big impact legally on what a winemaker can do to their must prior to fermentation, whether they can add alcohol/acidity or deacidify.
This was quite an intense class and we also covered canopy management, soil  types and characteristics, annual growth cycle of the vine and pest and diseases. For the last one pest and diseases you don’t need to know the life-cycle of phylloxera just what damage each pest/disease does to the vine and how to combat it.
Being the wine geek that I am I’ve signed up for a practical intensive one day course at Plumpton agricultural college in early March, where I’ll get a chance to prune vines and play in the vineyard. So I’ll try to revisit the topics I’ve not looked at fully here in a later post