There’s a lot that goes into making a great wine. Sunshine and rain, producer practices, and the interplay of grape variety with terroir all play a huge role in the bottle that eventually makes it to your table.
A lesser-known factor in the equation is yield, the amount of fruit harvested per area of vineyard. While it might not seem important at first blush, it plays quite a role in the final product, and virtually all of France’s AOC wines regulate maximum yields to maintain the quality standards of the appellation.
But what is the relationship between yield and quality?
In this article, we’ll go through some of the finer points of the question to give you a better understanding of why, when it comes to yield at least, less is often more.
In precise terms, yield is a measure of the amount of produce generated by a given surface area of vineyard land. In France (and most of Europe), the standard measure is hectoliters per hectare. In the US, it's ton per acre.
Because the first considers the volume of wine produced and the second the weight of grapes harvested, which can vary greatly based on vinification methods, there’s no exact conversion between these measures. But roughly speaking, 1 ton per acre comes out to roughly 15 hectoliters per hectare.
The relationship between yield and wine quality
Grapes ripen by drawing sugars and other nutrients from the leaves on the vine, which in turn draw on water, carbon dioxide, and sunlight to generate this vital energy. Since the amount of sunlight the vine can absorb is directly proportional to the surface area of its leaves, there's a hard limit to how much nutrition, pigment, and flavor compounds the plant can generate.
Since the fruit are all drawing from the same limited pool of sugar and nutrients, there’s a balance to strike between fruit and leaf surface area; between quantity and quality. The greater the fruit load, the fewer nutrients, pigments, and flavor compounds there are to go around.
In practical terms, too high a fruit load will result in greener, more acidic, diluted flavors and aromas. Conversely, cutting back the yield means sweeter, darker, riper, and more concentrated flavors.
This relationship isn’t exactly one-to-one. Cutting the fruit in half won’t double the sugars, but it can increase them up to 20%, a significant difference in the final wine. But while richer flavors are often a good thing, fewer fruit does not always translate to better wine. Fruit that is too ripe can lack character and acidity, and high sugar also means more alcohol.
For areas that don’t get much sun, this extra juice can be really helpful, but flavors that are too intense will overpower subtler notes, throwing the entire wine off balance.
If maximum yield is the aim, farmers push their vines to produce as much as 20 tons or more per acre, but this results in green, flat, watery wine. Indeed, voluntary reduction of yield reduces the number of bottles that a vineyard can generate, so low cost/low quality “bulk” wines tend to be produced from vines that are seldom subject to this reduction.
If maximum quality is the goal, the optimal amount for producing good wine is considered to be around 3–5 tons per acre (roughly 2250 to 3750 bottles) although this varies with grape and region.
Factors that influence yield
In general, there are three broad factors that play a role in a grapevine’s yield.
Some grapes are more prolific than others. Chardonnay is known as a very robust grape and will rapidly proliferate if given free rein. Pinot Noir, on the other hand, is notoriously finicky and lower-yielding.
Different grape varieties can also be more or less ‘yield sensitive’, which means their flavors taper off more quickly at higher yields. Pinot Noir is a common example, but red wines in general are a little more yield-sensitive than whites.
Age of the vine
Grapevines produce fruit for about a hundred years, but fewer and fewer as the vine ages. As a natural result, older vines tend to make grapes that are a little more concentrated in flavor. In France, many producers will identify the wines made with older vines (“vielle vignes”) because these are seen as an indicator of quality. While (surprisingly) there's no strict definition of when a vine can be considered old, it’s generally applied to those upwards of 40 or 50 years old.
Like most plants, grapevines need the right mix of sun and rain to adequately ripen. A particularly cloudy summer means less sunlight and consequently, fewer ripe grapes. A heavy rain around harvest time will result in grapes swelling with water weight, increasing yield. Pests, mold, frost just after bud break or at harvest, hail, extreme heat, and all sorts of other conditions can also damage grapes, reducing yield at harvest.
In addition to these more “natural” factors, producers often intervene to play a more active role in yield management. Winter pruning increases spring bud growth, prompting higher yields, while removing green fruit from the vine before it ripens (a practice known as ‘green harvesting’) is a common way of decreasing the fruit-to-leaf ratio and increasing concentration in the remaining fruit. Naturally, winemakers can also adjust the leaf side of the equation by adjusting the size of the canopy in vintages they believe to be overly sunny or rainy.
Since grapevines can only produce a limited amount of sugar and nutrients, increasing the yield beyond a certain limit generally has a negative impact on the resulting wine. Different grapes have a different range of tolerance, but the limiting factor of leaf surface area means that yields simply can’t be pushed beyond a certain point if the intention is to produce good wine.
Now, on its own, yield is not a determining factor in the quality of wine - but it is an important one. Lower yields don’t always mean a better wine, but in general it’s safe to say that too much fruit makes the wine suffer.
Knowing when to make the cut; when restricting yields is the right call is a large part of a viticulturalist’s savoir-faire, the knowledge of their craft. Good yield and canopy management is one of those marginal benefits that accumulate over the course of the winemaking process, and can make the difference between a wine that’s just good, and one that’s simply sublime.