As Hong Kong's financial year 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 its role in the wine sector is far more contentious. There are a variety of methods to calculate a vineyard's yield. It can be calculated based on grape weight (by tonnes per hectare) or by volume (litres of juice per hectare). Most of Europe bases its yield calculations on juice per hectare, typically stating the numbers in hectolitres (100 litres), 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 applied when crushing grapes will affect the volume of juice derived. Thickness of the skin, grape variety and size of berries also affect the juice quantity. Crop yields can range from 3 tonnes 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 if a vine invests its substantial resources in fewer grape clusters, the flavour, concentration and character are all bound to be higher quality. This theory is so embedded in the European psyche that yield limits are legally enshrined in most of the European Union's wine-growing regions. Burgundy's grand cru Clos-de-Beze, for example, must not produce more than 35 hectolitres per hectare. 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 a vineyard with low yields will not always produce high-quality wine. There are many factors affecting yield, including techniques used to control crop size such as pre-season pruning, shoot thinning and green-harvesting, which means removing excess grape clusters a few weeks before harvest. Some producers even 'reverse boast' when they discard excessive amounts of fruit onto the vineyard floor. Many contemporary viticulturalists argue the number of clusters per vine isn't as relevant as the number of leaves per cluster or the 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 pots, each with a spoonful of tea. In one, pour enough water to make two cups. In the other, pour enough water for six cups. The tea from the first pot will be dark and flavourful whereas the tea in the other pot will be pale and weak. Excessive foliage, however, is no solution. Leaves that shade one another offer no enrichment to the grapes, perhaps even diverting nutrients from the fruit. Dr Richard Smart, a respected viticulturalist, was one of the first to assert that the key to quality lies in the correct leaf-to-cluster balance. Smart advocates vine-training systems that give leaves maximum exposure to sunlight and healthy air circulation. This has led to widespread use of the Viagra-like vertical shoot positioning (VSP), whereby shoots are directed towards the sky and held into place by wires. Other methods include trimming, hedging or manually removing leaves - which all sound similar to the work of the financial sector.