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Gross Yield

By Debra Meiburg MW

As Hong Kong’s fiscal year end draws to a close, platoons of smartly-clad analysts will turn their attention to investment yields. The quest for high yield is unequivocal in financial circles, but the role of yield in the wine sector is far more contentious.

There are a variety of methods to calculate vineyards yields. Yields can be calculated based on grape weight (such as by tonnes per hectare) or by volume (such as litres of juice per hectare). Most of Europe bases its yield calculations on juice per hectare, typically stating the numbers in hectolitres (100 litres) per hectare, abbreviated as hl/ha. Non-European producers are more likely to measure by grape weight, arguing that juice volume can be manipulated during winemaking and so does not accurately reflect what was produced in the vineyard. For example, the amount of pressure used when crushing or pressing grapes will directly affect the volume of juice derived. Thickness of skins, grape variety and size of berries all affect the final juice quantity as well.

Grape vines are obliging plants and crop yields can range from 3 to 40 tonnes of fruit per hectare. It has long been the industry’s mantra that low crop-yields result in fine quality wines, the theory being that if a vine invests its substantial resources in fewer grape clusters, the flavour, concentration and character is bound to be higher quality. The link between low yield and high quality is so embedded in the European psyche, that yield limits are legally enshrined in most of EU’s wine growing regions. Burgundy’s grand cru Clos-de-Bèze, for example, must not produce more than 35 hectolitres per hectare (35 hl/ha).

It is true that most of the world’s finest wines are produced from vineyards with low crop yields, but the relationship between yield and quality is not necessarily cause-and-effect. In general, excessive yields result in low quality, but it doesn’t follow that a vineyard with low yields will always produce high quality wine. There are many factors affecting yield, but the most common techniques used to control crop size is pre-season pruning, shoot thinning and green-harvesting, which means removing excess grape clusters a few weeks before harvest. The low-yield mentality has become so pervasive that producers “reverse boast” that they discarded two tonnes of fruit onto the vineyard floor.

Many contemporary viticulturalists argue that the number of clusters per vine isn’t as relevant as the number of leaves per cluster, or leaf-to-cluster ratio. Healthy leaves generate the carbohydrates that provide the flavour compounds, ripe tannins and sweetness to the grapes. Vines with low leaf-to-fruit ratio (too many grape clusters) ripen more slowly and in many cases will not reach full maturity before harvest. Imagine two tea-pots, each with one spoonful of tea. In one, pour enough water to make two cups of tea. In the other, pour enough water for six cups. The tea from the two-cup pot will be dark and flavourful whereas the other pot supplies tea that is pale and weakly flavoured.

Excessive foliage, however, is no solution. Leaves that shade one-another offer no enrichment to the grapes, perhaps even diverting precious nutrients from the grapes. Dr. Richard Smart, arguably the world’s most respected viticulturalist, was one of the first to assert that the key to quality lies in the correct leaf-to-cluster balance. Dr. Smart advocates vine training systems that give leaves maximum exposure to sunlight and healthy air circulation, which has led to wide-spread use of the viagara-like vertical shoot positioning (VSP) where shoots are directed toward the sky and held into place by training wires. Other methods include trimming, hedging or manually removing leaves – all sounding similar to the work of the financial sector this week.

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