California grapes: quantity versus quality

Grape production is a balancing act between quantity and quality — producing a greater quantity is usually assumed to result in a reduction in quality. Therefore, attempts by grape growers to increase grape quality are usually associated with trying to decrease quantity. The relationship works both ways.

It is therefore of interest to look at the big picture of this supposed relationship. This quality/quantity relationship is usually investigated only at the micro level — for example, individual growers might decide to increase their grape quality by thinning their crop. But what happens at the macro level, across all growers? This question seems rarely to have been asked.

One simple way to start looking at this topic is to compare the production area of particular grape types with the amount of fruit they produce. We might anticipate that the highest quality varieties produce less fruit than do lower quality varieties. This is a simplistic approach, of course, because there are many factors that affect fruit production, most notably the weather; but if we restrict ourselves to a particular viticultural area, then it might be a useful place to start.

So, I decided to look at the California grape data provided by the United States Department of Agriculture (USDA). The latest report is from April 2017, which shows the acreage of productive vines (in each US state), for both red varieties and white varieties. I then compared these data to the data for the 2016 California grape crush provided by the American Association of Wine Economists (AAWE), for the top reds and top whites.

The data are shown in the two graphs, one for each type of grape. Within each graph, each point represents a single grape variety in California, showing its bearing acreage horizontally and its grape crush vertically. The lines on the graphs are best-fit linear regressions, illustrating the "average" production expected from each variety based on its acreage. In both cases the lines fit the data quite well, explaining c. 85% of the variation in the data.

The first graph shows the data for the red varieties, where Cabernet sauvignon is by far the most widely planted grape variety, as well as the one most highly esteemed by winemakers. I therefore calculated the regression line, as shown, without including this variety, so that the line is fitted only to the other varieties — this then tells us what production to "expect" from Cabernet, based on the observed data for the other varieties. We can see that, as anticipated for the top variety, Cabernet sauvignon produces a much smaller crop than do the other varieties.

Interestingly, both Zinfandel and Rubired (labeled on the graph) produce a larger grape quantity than we might expect from their acreage, whereas all of the other varieties are close to their expectation. This is notable because Zinfandel is the second most widely planted red grape, and it is usually considered to also be a premium variety. Other common premium varieties, such as Pinot Noir, Merlot and Syrah, produce crops at about their expected level in California.

A similar pattern is seen when we look at the white grape varieties, as shown in the second graph. Indeed, the regression lines in both graphs have almost the same slope (and intercept), indicating that red and white production both have the same relationship to area.

Chardonnay is both the most widely planted white grape variety and the one most highly esteemed by winemakers. It is obvious from the graph that Chardonnay produces less quantity than is expected based on the other white varieties, as anticipated.

Interestingly, three of the next four most widely planted white varieties (labeled on the graph) produce a larger grape quantity than we might expect from their acreage, whereas all of the other varieties are close to their expectation. This matches the pattern observed for the red varieties, where only the top variety has a reduced crop.

Finally, the California Department of Food and Agriculture's California Grape Crush Report Preliminary 2017 allows us to look at the broad-scale economics of wine-grape production. The graph below shows the inflation-adjusted price per ton of wine grapes (vertically) versus the grape crush tonnage (horizontally). Each point represents the crop for one year from 1989 to 2016, inclusive.

As can be seen, for the white-wine grapes their price is unrelated to the crop size — prices do not go up or down when the crop is large. On the other hand, for the red-wine grapes the price has a tendency (ie. with a few exceptions) to rise when the crop is large (correlation = 33%). In both cases, price is not related to scarcity, which is the important point. This implies that voluntarily restricting crop size does not affect the overall economics — the reduction in crop is likely to be compensated by increased price.

Conclusion

So, Cabernet sauvignon and Chardonnay are the most widely planted and most esteemed red and white grape varieties, respectively, in California, and they both produce smaller crops than might be expected based on the production levels of other varieties. Furthermore, the situation differs for some of the other widely planted varieties, which produce larger crops than might be expected. This seems to match what is anticipated from the suggested relationship between quantity and quality — quantity is less when quality is at its very highest. For California grapes, less is more.