The term “yield” is used in viticulture to establish the number of kilos of grapes that are generally obtained per hectare of vineyard. This will be fundamentally conditioned by the number of vines planted and the number of clusters stipulated by each plant. Thus, there are vineyards that have 1,500 vines per hectare, in the same way, that there are vineyards with 10,000 vines per hectare.
We can also find vineyards that deliver 6 kilos of grapes per vine, contrasted with others that deliver 500 grams or less for each one (at least two vines are necessary to produce a bottle of wine). Of course, it is the winegrower who makes the decisions that will define the vineyard’s performance, conditioned by a series of factors, some permanent, and other variables, throughout the year and over the years, such as:
- The higher the humidity and the fertility of the soil, the more convenient it will be to plant more vines per hectare, thus generating competition for water and nutrients, being exactly the opposite in dry and poor soils. This competition that is promoted between the vines helps to control the vegetative expression of the plants (it must be remembered that the vine is a climbing plant that constantly seeks to expand its branches).
- Climatic conditions (hours of sunshine, rainfall, frost, etc.).
- Diseases and pests on vines.
- The characteristics of the grape variety.
- The age of the vineyard.
- Cultural practices (driving system, fertilizers, etc.).
- Limitations of the regulations (for example, an appellation of origin).
- The type and amount of irrigation (if allowed).
Now, with the vineyard already established and the number of vines in it determined, the pruning work on the plant is the fundamental weapon that the winegrower has to regulate the “load” or quantity of clusters, controlling thus the overall performance. In this sense, shoot pruning is carried out to improve lighting, bunch pruning so that the plant distributes its resources among fewer bunches (higher concentration), and leaf removal to optimize light capture and photosynthesis. Of course, all the above is done to the proper extent and based on analysis.
During pruning, to evaluate the balance between vigor and production, the so-called “Ravaz Index” is used, which is the result of dividing the kilograms of grapes collected by the kilograms of shoots removed during pruning. The optimal value resulting from this calculation should be between 5 and 9, thus limiting the number of clusters to the photosynthetic possibilities of the plant, preventing it from being excessive or insufficient, which could affect both the fruit and the vine.
An excessive yield can alter the maturity, cause diluted wines of lower quality and premature aging of the vine, and an insufficient one can generate extra vigor in the buds, as well as a very alcoholic wine or with tastes of “compote.” Both situations harm the quality of the grape and the regularity of the harvests. But anyway, we reiterate, not all grape varieties behave the same, with some that deliver an abundance of fruit without problems and others in which this undermines quality.
It is also important to pay attention to the leaf area, that is, to the surface of the leaves, since the relationship of said leaf area with respect to the number of clusters and their weight must be taken into account, considering that photosynthesis strongly determines the level of sugar in the berries, among many other factors, always highlighting that not all varieties of strains are handled the same, nor do they need the same requirements, this being even more complex, depending on the environment in which they are found.
But in general rules, should we say that a higher yield undermines the quality of the fruit and vice versa? I don’t know if that question has a blunt answer. Quite possibly, the answer is “yes,” but in viticulture, rarely one plus one is two. It depends on many factors. Furthermore, a vineyard with low yields due to having few vines is not the same as having many vines with few bunches. A priori, the second is preferred. What can be said without problems is that a plantation must be balanced to have high chances of achieving good quality, knowing all the factors listed above.
It will depend on how the vineyard has been cared for and worked, not in one year, but in the succession of many harvests, and on how the requirements of the terroir have been managed since its creation and throughout its life. This balance in the vineyard, generally tending to moderate to low yields, will promote maturity and the correct concentration of the fruit in color, aromas, sugars, pH, acids, polyphenols, and all the qualitatively important elements to achieve a successful wine.