For a long time, everyone involved in the world of wine has been familiar with, or has at least heard of, concepts such as low-yield or controlled-yield vineyards, old vines, or dry-farmed vineyards as keys to making quality wines.
In this article we take a closer look at the physiology of the vine from a theoretical point of view and bring that theory down to the actual conditions in the vineyard, in order to assess, or rather demystify, some of these popular concepts, which have often been used for marketing purposes to increase the commercial value of wines produced in certain parts of the world.
Let’s look at the concepts commonly used today as tools for marketing wine.
Low yields as a driver of quality
To someone unfamiliar with vineyard management, low yields per hectare can be a very convincing sign of quality when buying a wine. The idea is usually, and mistakenly, associated with vines that produce little fruit and can therefore concentrate all the aromas, color, tannins and so on, that is, all the desirable compounds that characterize a quality wine. In certain circumstances this may be true, but as we will see below, there are times when it is not.
Vineyard yields are usually measured either as a mass of grapes per unit of area, such as tons per hectare or tons per acre, or as a volume of wine per unit of area, such as hectoliters per hectare or hectoliters per acre.
This single yield figure says absolutely nothing about the quality of the grapes produced in that vineyard in terms of the concentration of their components. A very simple, real-world example illustrates this.
Suppose a vineyard in a given area produced 8 tons per hectare in a given year, but 50% or more of the vines were diseased or dead. That means the yield was achieved by the healthy vines alone. If the vineyard had been 100% productive, the real yield would have been 16 tons per hectare, a figure that few places in the world would consider low.
Other parameters are far more meaningful for measuring yield, such as yield per vine, planting density and the health of the vineyard.
In addition, what counts as a low yield in quantitative terms varies considerably by wine region (climate, terroir, resources) and by local growing practices. For example, a pergola-trained vineyard in central Chile managed for low yields may well reach 12 tons per hectare, which in Baja California, Mexico, or in any other region with low viticultural potential, might be considered a very acceptable yield, and, depending on the style of wine, even a questionable one for quality wines.
Potential yield
The potential yield of a grapevine, that is, the maximum number of clusters it can produce (though not necessarily bring to full ripeness), is set at pruning, or more precisely by the number of buds left on the vine when it is pruned. Each of these buds has the chance to grow a shoot that will bear clusters, so the more buds are left on a vine, the greater its potential yield.
Besides clusters, shoots also produce leaves, which are responsible for synthesizing sugars, acids, aromas and polyphenols in general. Pruning therefore also determines the vine’s leaf area and, with it, its future ability to synthesize these compounds.
Conclusions
From the above, we can see that it is not enough simply to state the quantity of grapes produced per unit of vineyard area, since this single number does not necessarily reflect the quality of the grapes produced.
From a technical point of view, it is more useful to express yield as the quantity of grapes produced by the vines that are actually productive within a vineyard.
The quality of a wine is largely determined by the amount of desirable compounds it contains, some of which come from the vineyard while others develop during processing in the winery. Producing grapes rich in desirable compounds, whether aromas, aroma precursors or phenolic compounds, through viticultural practices is only one step toward making memorable wines.
Managing yields to concentrate these compounds is essential, and it is just as essential to keep the vineyard balanced and healthy as a productive whole, so that all the vines in it, which share similar natural resources, are performing at acceptable levels of productivity.