Monday, August 12, 2019

How similar is the wine quality of the Bordeaux First Growth chateaux?

We are always being told about the Premier Cru (First Growth) wines of Bordeaux, as though they are the pinnacle of red wine-making. Now, I have had only a few of these wines, but I have realized that they are not really to my taste; so their outrageous prices do not concern me, personally.

Nevertheless, I have sometimes wondered about the quality relationships between these wines. Which chateaux get high scores in the same years, and which ones do not? This seems like precisely the sort of question that I try to answer in this blog.

This is actually straightforward, because I have already used suitable data in some previous posts (How large is between-critic variation in quality scores? ; Wine-quality scores for premium wines are not consistent through time ; The sources of wine quality-score variation).

The data consist of wine-quality scores for the five premier cru Bordeaux chateaux (Latour, Lafite-Rothschild, Margaux, Mouton-Rothschild, and Haut-Brion) for each of the vintages 1988–2014, inclusive. This makes a total of 195 wines. The scores come from: Jeff Leve, Robert Parker, Jean-Marc Quarin, Jancis Robinson, La Revue du Vin de France, and the Wine Spectator.

There are thus three sources of possible variation in the set of quality scores:
  1. between the 5 chateaux
  2. between the 6 commentators
  3. between the 27 vintages.
The first one is the one I am studying, which means that I need to decide how to address the other two, so that the chateaux comparisons are correctly made. One simple way to address the third source is to average the scores across the years, for each commentator. This leads to two data analyses: one based on the original data, and one based on the averaged data — their difference will tell us how much vintage variation affects the relationships.

As I have done in previous posts, I have used a network to visualize these data, with the network being used as a form of exploratory data analysis. I first calculated the similarity of the different wines, based on the quality scores, using the correlation coefficient. I converted this to a distance measurement; and then used a neighbor-net analysis to display the between-chateaux similarities as two phylogenetic networks.

For the interpretation of such networks, see the post on Summarizing multi-dimensional wine data as graphs, Part 2: networks.

The first network, based on all of the scores for each vintage and each commentator, is rather uninformative. This means that the between-vintage variation is fairly large, and is thereby obscuring the topic of interest (the relationships among the chateaux). However, there is some indication of similarity in quality scores between Latour and Lafite, and between Mouton and Haut Brion.

Network of wine quality for premier cru Bordeaux wines

So, we need to investigate these patterns further, by reducing the effect of between-vintage variation. As noted, this can be done by averaging the scores across the vintages, before producing the network. The result is shown in the next graph.

Network of wine quality for premier cru Bordeaux wines - averaged across years

Things are now much clearer. Indeed, the quality scores for Latour and Lafite are very similar to each other, as are the scores for Mouton and Haut Brion. Margaux is placed in an intermediate position between the latter two.

So what do we conclude from this? First, we can note that there actually are patterns in the data, rather the whole thing being random — certain chateaux do follow each other in terms of variation in wine quality (at least as assessed by the 6 score sources included here).

Second, we might not be surprised that the Margaux wine is different from the others, since it is geographically separate from the others, in the Margaux commune of the Haut Médoc. Similarly, we might not be surprised that the the Lafite Rothschild and Latour wines are similar, since they are both located in the Pauillac commune of the Haut Médoc (although one is in the north of the commune and the other is in the south).

However, our third point might be that Mouton Rothschild is also located in this same commune of Pauillac, and yet its wine quality is most similar to that of the Haut Brion wine, which comes from the Pessac area of Graves. Indeed, these two chateaux are almost the furthest apart of the 5, geographically, while the closest chateau to Mouton is actually Lafite. You might like to think of an explanation of this pattern for yourself.

This obviously leads on to an assessment of the 1855 classification of Bordeaux wines, which I will tackle in a future post.

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