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dimanche, 23 février 2014

VITICULTURE

GREEN HARVESTING: A CONTROVERSIAL TECHNIQUE


Claude Gilois

Green harvesting involves reducing the quantity of grapes on a vine just before the grapes change colour (veraison). Yields are reduced and the juice in the remaining grapes will be more concentrated and will result in better wine being made; at least that's how the theory goes.  If it is done too early the vines will compensate by producing bigger grapes hence cancelling the effects of the green harvest.

 

This technique is far from being uncontroversial; many see nothing but a fad that does not contribute to better wines being made. They argue that if vines are properly taken care of they will regulate themselves. Most critics see green harvesting as either insufficient pruning that results in larger yields, or the use of inappropriate rootstocks that are too vigorous, or simply bad handling of fertilisers in the vineyard.   It is true that it is tempting to prune long, leaving more buds just in case the flowering is difficult and to rectify the situation later by green harvesting if the flowering has been normal and the load on the vine too prolific. 

It is highly controversial that 15% green harvesting will reduce the juice being produced by the grape by 15%.  Many winegrowers, particularly in Burgundy, are very sceptical about it and they are prepared to accept that some vintages will be more or less generous depending on the weather conditions. 

The problem with green harvesting is somewhat more complicated in regions where climatic conditions are more variable (Bordeaux and Burgundy for example) where the amount of grapes to be dropped at green harvest is decided on a weather pattern that is very uncertain as climatic conditions can vary enormously in August and September.   It is, therefore, a very empirical technique based on the winegrowers’ feelings of weather conditions still to come, but they know that yields need to be low if great wines are to be produced. In warmer climates, where the weather pattern is more consistent then it is not such a problem as weather predictions are on the whole more consistent. 

It is Petrus who was the first to use this technique in 1973, Margaux followed in 1986. Quite a few domains only green harvest on young vines, as they tend to be more vigorous hence more prolific, but some notorious winegrowers do not share this point of view. Manfred Krankl from the domain Sine Qua Non in California argues that it is possible to control the vigour of young vines, by reducing inputs to young vines from the start which will allow them to control themselves. Green harvesting argues Bruno Prat from Cos d’Estournel is a bit like pushing the accelerator and the brake pedal at the same time. 

The critics of green harvesting see the technique as of form of an insurance policy.  They argue that if you want 50 hl/h it is easier to prune for a yield of 75 hectolitres per hectare. If the flowering is good you can green harvest to obtain the 50 hl/h that was your original target. If the flowering is poor then there is no need to green harvest as you will not be far off your target. 

But is really that simple?   Paul Draper from Ridge does not agree: “The conditions on Monte Bello where Ridge vineyards are located are very difficult once every three years, “We have poor sets and the yields can drop drastically. It unbalances vines and they do not produce such good grapes”, he adds “It may be that yields of 25 hl/h are fine in France, but in California where the weather pattern is more constant and the weather conditions warmer, low yields are not necessarily best as the vines can bear a more important proportion of fruit than in cooler countries”. Finally. he adds “I do not see this as an interventionist technique, it is more like coaxing the vines to give you the best possible results”. 

As usual with vines and wines it is not straightforward, it is all about compromise.  Too much or too little yield will create an unbalance in the vineyard.  It is true that low yields probably unbalance vines more in warmer than in cooler countries. It is the balance between the foliage and the number of grapes that is most important; this balance will create more or less yields depending on the location of the vineyards and the climatic conditions.

 

 

 

 

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