If there is an axiom of wine lore that is sacrosanct, it’s the belief that lower yields translate into better wine. But do they?

Let’s start with some grape growing basics. Like any living organism, the grapevine needs energy sources to drive its biological functions. The vine’s leaves are what transform sunlight into carbohydrates, the grapevine’s food. This is the “source” of the vine’s energy system.

That energy is then used by the grapevine. A place where the energy is used is called a “sink”. There are two main sinks: vegetative growth (leaves and the canes that they are attached to) and the fruit.

At the beginning of each growing season, the vine’s buds start growing (”budburst”). Each of those buds produces a cane with a limited number of fruit clusters (two is normal). That cane, however, has no corresponding built-in limit on the number of leaves. While each cane can produce only a few fruit clusters, no matter what, it can go on and on producing more and more leaves as long as the energy is available. The only thing that keeps the canes from growing longer and longer is the fruit, by competing for the vine’s resources.

As a grape grower, what you want to see is a vine that devotes the early part of the season to producing leaves, and then switches over mid-season from leaf growing to fruit ripening.

A grapevine with too little fruit is “undercropped.” Since the fruit sink is small, the vine keeps feeding the vegetative sink (i.e., growing more leaves). The result is not just lower yields, but poorer fruit quality as well. Since the fruit can’t compete successfully with the actively growing canes, it doesn’t get the nourishment it needs. To add insult to injury, the heavy vegetation shades the fruit (not a good thing) and creates a closed-in canopy that both promotes unwanted infections and hinders the penetration of the sprays that combat those infections.

The opposite of “undercropping” is “overcropping,” where too much fruit is left on the vine. The excess fruit appropriates the vine’s resources at the expense of vegetative growth. Without enough leaves, there’s not enough nourishment to produce high quality fruit. An overcropped vineyard may produce lots of mediocre fruit.

So what the grape grower wants is a vine that’s “in balance,” with the right amount of leaves in relation to the fruit. While a number of ways of determining when a vine is in balance have been developed, one of the simplest is one of the best-canes should grow to be about four feet long. Since there is no way of directly regulating the amount of vegetative growth, we achieve this balance indirectly by regulating the amount of fruit on the vine (i.e., more fruit, fewer leaves and shorter canes). The main way of doing this is by leaving the right number of buds on the vine at pruning time.

What is the right number of buds? It depends on many factors. The vineyard’s climate and the fertility of its soil are critical. The choice of grape variety, as well as the rootstock (the underground part of the vine that the grape variety is grafted onto), will also affect how much fruit the vine can support. No mathematical formula can tell you the right number of buds to leave-only the grape vine can do that. At pruning time, you take a look at the vine and see how it did last season. If it was too vigorous, you increase the number of buds, and vice versa.

If you have low producing varietal planted in a relatively cool location on poor shallow soil, the vines can only produce a small crop. A vigorous variety planted in deep rich soil in a warm location can produce a much larger one. Both vines have, in theory, the ability, to produce high quality fruit.

So let’s take two vineyards, each of which produced 4 tons per acre last season. The first had short stubby canes; the second very long ones. The first vineyard should be “pruned back”, that is, left with fewer buds, which will reduce its yield, but result in better fruit. To the do the same with the second vineyard (applying the formula that lower yields automatically translate into better quality) would be a horrible mistake. That vineyard should be less severely pruned (i.e., leave more buds and therefore more fruit), which will increase both quantity and quality. Both vineyards should be allowed to produce whatever amount of fruit will result in balanced vines. If that turns out to be 2 tons/acre in one, and 8 tons/acre in the other, then so be it.

In the end, the goal is not to mindlessly reduce yields, but to find that yield (high or low) that allows the vine to come into balance, at which point the quality of its grapes will be the best that they can be.