Monday, August 8, 2016

Fifty years of Bordeaux vintages

Vintage charts are intended to show us how the harvest quality has varied from vintage to vintage. They are often disparaged, because they simplify the complexities of each harvest (where there can be considerable spatial variation) down into a single number. They also make little sense if they are applied to a very large area, which they too often are in practice.

Nevertheless, they can be an interesting and informative guide to the general features of each vintage within a restricted area, even if they tell us nothing about each wine producer within that area, and how each producer dealt with the vagaries of harvest time.

This particularly applies to those vineyard regions where there is a long series of vintage assessments. In these cases, we can study the long-term patterns of vintage variation, without needing to concern ourselves with differences between individual producers, within or between vintages.

There are several regions where the written vintage records go back at least a century, and I will be covering these over the next few weeks. For example, there are several series for both Bordeaux and Piemonte, as well as a very long one for the Rhine valley.

Here, I will start with a somewhat shorter series, covering only a half-century, but which I will analyze in some detail.

The Wine Cellar Insider Bordeaux Vintage Ratings, 1959 to Today

Jeff Leve, at The Wine Cellar Insider, has provided vintage rankings for the red wines of the Bordeaux region of France, for every year from the famous 1959 vintage up to and including 2014 (ie. 56 vintages). This assessment is based on the standard 100-point quality scale (ie. ranging from 50–100). The data are shown as a time series in the first graph.

Bordeaux vintage quality 1959-2014

This graph shows several interesting features.

First, there is no score between 50 and 60, and also no score between 70 and 80. This means that three distinct types of vintages can be recognized: 1 disastrous vintage (score 50), 11 mediocre vintages (score 60-70), and 44 good vintages (score 80–100). This is a pretty impressive record for the vignerons.

Second, there is no score of 94, and so we can conveniently score "great" vintages as being ≥ 95 points (this is the pink line on the graph). This gives us 9 such vintages, out of the 44 "good" ones, which is also pretty good for the wine-makers. Oddly, there are no scores of either 98 or 99, but there are two scores of 100 points.

Third, there have been no mediocre vintages since 1992, and only two mediocre vintages after 1980. Before that, there were 10 mediocre vintages and 12 good ones. Indeed, before 1993 there were 5 great years, 17 good years, 11 mediocre years and 1 very poor year (in 34 years), while since then there have been 4 great years and 18 good years (in 22 years). This is quite a dramatic change in fortune during the latter part of the series.

This change has often been attributed to improved vineyard management since the 1990s. In particular, nowadays there is usually much more rigorous selection of grapes at harvest, so that poor grapes are simply not included in the best wine. In this sense, it has been claimed that there are no longer "good" years and "poor" years for vintages, but instead there are years with a larger or smaller amount of good wine.

There are also what are called "green harvests", which refers to the taking of unripe (ie. green) bunches of grapes off the vines a few weeks before harvest. This results in uniformly riper grapes, which ensures softer tannins in the ensuing wine, as well as reducing the yield, and thus concentrating the flavor in the remaining grapes. There has also been a recent trend towards late picking of ultra-ripe grapes, which makes the wine more fruity (and more alcoholic). This all makes today’s wines drinkable earlier than those of 20 years ago.

Relationship between Bordeaux vintage quality and summer temperature

However, Orley Ashenfelter (see the references listed below) has suggested, instead, that the recent improvements in harvest quality may actually be due to increased summer temperatures. That is, higher temperatures during the vines' growing seasons have mitigated the need for fancy vineyard management. The relationship between the daily-average summer temperature and the vintage quality score is shown in the second graph, for the period 1959–2009 (the temperature data come from Ashenfelter and Pablo Almaraz). Each point represents one Bordeaux vintage, mapped by its average temperature (horizontally) and its quality score (vertically).

These data show that, mathematically, 37% of the variation in the vintage quality scores during the past half-century is related solely to variation in the summer temperature. Clearly, summer warmth has a large influence on improving harvest quality.

Moreover, the distribution of the summer temperatures in Bordeaux over time from 1952–2009 is shown in the third graph. The pink points indicate the years from 1989 onwards (as they also do in the previous graph), showing that there has been a significant increase in daily-average summer temperature since that time. Indeed, there has been a steady increase in temperature since the low of 1977. European vignerons are in no doubt about the existence of global warming!

Bordeaux summer temperature 1952-2009

Ashenfelter backed up his original assessment of the relationship between vintage quality and summer temperature with some forecasts (inaccurately called "predictions"). These appeared in the New York Times in 1990: Wine equation puts some noses out of joint.

The first forecast was for the 1989 vintage:
Perhaps the most dramatic Ashenfelter prediction is for the 1989 vintage. By Professor Ashenfelter's calculations, the hottest growing season in memory, combined with a very dry harvest, all but guarantee that the 1989 Bordeaux will be stunningly good.
Jeff Leve's assessment in 2015 (15 years later) was a score of 95 for the 1989 vintage. So, this forecast turned out to be spot on.

The second forecast was for the 1986 vintage:
According to the Ashenfelter system, below-average growing season temperatures and above-average harvest rainfall doom the 1986 Bordeaux to mediocrity. When the dust settles, he predicts, it will be judged the worst vintage of the 1980s, and no better than the unmemorable 1974s or 1969s.
Jeff Leve's 2015 assessment was: 1969 vintage = 60 points, 1974 = 65 points, and 1986 = 88 points. Furthermore, there were five worse vintages than 1986 during the 1980s, and four better ones. Indeed, the worst vintage of the 1980s was 1980, with 70 points. So, this forecast was pretty far off.

Literature references

Pablo Almaraz (2015) Bordeaux wine quality and climate fluctuations during the last century: changing temperatures and changing industry. Climate Research 64:187-199.

Orley Ashenfelter, David Ashmore, Robert Lalonde (1995) Bordeaux wine vintage quality and the weather. Chance 8(4):7-14.

Orley Ashenfelter (2008) Predicting the quality and prices of Bordeaux wine. Economic Journal 118:F174–F184.

Orley Ashenfelter (2010) Predicting the quality and prices of Bordeaux wine. Journal of Wine Economics 5:40-52. [a reprint of the previous paper]

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