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A Good Root: Grape Vine Rootstocks and Their Effect on Wine Quality
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There is a saying that has become a bit of a cliché that 'wine quality is created in the vineyard'. Now, from a person who has always seen things from a winemaking perspective, I am at great pains to admit that the claim is absolutely true! Except for the usual unexplained mysticism surrounding the concept of 'terroir', very little has been written about the real role that viticulture plays in wine quality. It's a huge topic, but where better to start off than with the vine itself.
It is a little known fact that the vast majority of vines planted world-wide use the roots of another vine to extract the water and nutrients they need from the soil. When you drive around your favourite wine-growing region, the bits you see above ground, whether they be Shiraz, Semillon or Chardonnay, belong to the European vine species, Vitis vinifera. However below ground, you may be surprised to find out that in many cases, the roots of these vines belong to another species of vine altogether.
The roots of V. vinifera are particularly prone to two devastating soil borne pests; the dreaded grape louse, Phylloxera and the lesser-known but far more widespread microscopic worm like group of parasites called Nematodes. The Europeans found this out with devastating effect in 1863 when Phylloxera, a bug that is native of the United States, was inadvertently introduced. It resulted in the death of countless millions of vines in France alone. Phylloxera is the the 'black plague' of vines. It is an insect that has both a soil borne and winged form, and as such, all attempts to eradicate it using chemical or other sterilisation methods were ineffective. But a solution was found. Many of the wild vine species native to the US such as Vitis berlandieri, V. riparia and V. champini had built up a natural resistance to Phylloxera. These obscure relations to the European grapevine are in fact weedy, sprawling plants that inhabit creek beds or baking hot plains. They all produce disgustingly tart and bitter fruit. Grapes I suppose, but you would have to be somewhat Nethanderthal to think so. However, by grafting the wine grape V. vinifera onto the roots of these species (or their crosses), it was found that the resulting vine rootling could withstand the ravages of phylloxera.
The root part of this grafted plant is called a rootstock. Over the next century, breeders made many complicated crosses of these obscure American species. The best crosses were propagated in their millions and were given the now mystical names like '1103 Paulsen', '5A Teleki', '101-14 Millardet' and '110 Richter'. Later it was found that as well as affording various levels of protection against phylloxera, vines grafted onto various rootstocks grew better in saline, acidic, clay, limestone or drought ravaged soils, and most produced significantly higher grape yields compared with vines grown on their own roots. Paydirt!
But what are the effects of using rootstocks on wine quality? I was fortunate enough to have been involved in a number of rootstock comparison trials undertaken by the Roseworthy based Grape and Wine Research in the 1990's. The same variety was grown on different rootstocks at the same vineyard site. Each wine, representing the effect of each rootstock was made in exactly the same way, and as scientific method requires, they were made in triplicate. When placed side by side, the differences were remarkably consistent and obvious. When young, the rootstock wines typically had slightly less colour depth and had distinctly more lift to their aroma than did the own rooted wines. The own rooted wines typically had a little more flavour depth and were brighter red in hue than most of the rootstock wines. Paradoxically, their aroma was distinctly closed. Despite the comparison it must be said that most of the rootstock wines had more than commercially appropriate levels of flavour, tannin and colour. At age four, the value of growing vines on their own roots was revealed. The ungrafted wines were much darker in colour, and were much redder (in that they had less of the brick hues) than the rootstock wines. Once again, they had more flavour, but this time the aromas had now overtaken the rootstock wines in intensity. In short, the ungrafted wines had significantly better aging potential. Perhaps this is why the Bordeauxlaise long for the pre-phylloxera days of a century and a half ago. However, given the reality that most wines are consumed immediately after being purchased, and that the use of rootstocks typically results in twice the number of kilos per vine, one can readily appreciate the commercial aspects of using rootstocks.
Unfortunately, Australia's most widely used rootstock has consistently shown to be a poor performer in the quality stakes. The rootstock 'Ramsey' (Vitis champini) has been popular for many decades as it produces very high yields and is well suited to the relatively coarse, infertile and saline soils of the inland irrigated regions of Australia. However, unless very carefully managed, it can impart a lot of vigour to the vine, resulting in dense canopies that shade the fruit during their ripening. This results in wines of low colour, unripe characters, lower alcohol levels and most importantly higher pH's which result in rapidly ageing wines. All of the Ramsey wines in the Roseworthy trials were tired at age four, regardless of which region they were sourced. Frankly, most were completely 'stuffed' despite being cellared well. Keep in mind that viticulturists have developed ways of curtailing Ramsey's vigour, through the use of deficit irrigation and pruning methods that result in large numbers of devigorated shoots which effectively open up the canopy to light. Seems like a lot of mucking around to me though.
So next time you visit your favourite winery, forget about asking about what oak they are using. Why not ask about if there vines are on rootstock and if so, which? It's a good question as the rootstock on which the fruit was spawned would have at least as much an impact on the wine that you are drinking.
Gawel, R., Ewart, A. J. W. and Cirami, R. (2000) Effect of rootstock on the composition, aroma and flavour intensity of wines from the scion Cabernet Sauvignon grown at Langhorne Creek, South Australia. Australian and New Zealand Wine Industry Journal, 15, 67-73.
Ewart, A. J. W., Gawel, R., Thistlewood, S. P. and McCarthy, M. G. (1993) Effect of rootstock on the composition and quality of wines from the scion Chardonnay. Australian and New Zealand Wine Industry Journal, 8, 270-274.