Having established that the winemakers have been moving towards a greater diversity of grape varieties in Opus One, we can now ask whether this has improved the wine quality in the eyes of the drinkers. For the rest of the grapes, it has been c.7% merlot, c.6% cabernet franc, c.6% petit verdot, and c.1% malbec. In the early years, there were vintages composed of >95% cabernet sauvignon, but over the past 10 years it has been closer to 80%. This has been partly the result of using five grape varieties, as opposed to the original three, but it is mainly a result of using greater proportions of the minor varieties. Furthermore, from the early 1990s onwards the diversity has steadily increased. This graphs shows that there was a lot of variability between the first few vintages, while the winemakers worked out what wine style they were aiming for. The variation in Shannon diversity is shown in the first graph, with the vintages plotted horizontally and the diversity plotted vertically. The data for each vintage come from the Opus One web site. This Index will be a number between 0 (for a single grape variety) and the natural logarithm of 5 (for equal amounts of each of the 5 varieties). The one I will use here is called the Shannon Diversity Index (see Wikipedia). The idea is to reduce the proportions of the various grape varieties down to a single number (for each vintage) that quantifies their diversity, from a single grape variety at one mathematical extreme to equal amounts of each grape variety at the other extreme. A number of mathematical measurements of diversity have been developed in science, for making precisely this sort of comparison. In this blog post I wish to look at the variation through time in the diversity of the grape varieties within the wine. Michael Silacci has been the chief winemaker since 2001, early on with either Tim Mondavi or Philippe Dhalluin, but alone since 2004. The winemakers were Tim Mondavi and Lucien Sionneau from 1979–1984, and Tim Mondavi and Patrick Léon from 1985–2000, with Genevieve Janssens assisting from 1991–1997. The proportion of these grape varieties in the wine has varied from year to year, as determined by the winemakers. Then, malbec was added to the blend in 1994, and petit verdot was added from 1997 onwards. The wine started out as a blend of mainly cabernet sauvignon, along with some cabernet franc and merlot.

I contend that it has at least something to do with the variation in grape varieties. Ridge Monte Bello has a similar Bordeaux-style aim), although they all sell considerably fewer than the 25,000 annual cases of Opus One. Certainly, other wines have surpassed it in price and/or reputation (e.g. It has struggled to maintain that reputation, as it has been persistently criticized for inconsistency from vintage to vintage. It was the first ultra-premium wine from the USA, the California equivalent of a Bordeaux first growth, intended as a benchmark for the wines produced from cabernet grapes in the Napa Valley. This wine has been known as Opus One, with its first vintage in 1979. (They used also to contain Carménère, but that grape is now rare in Bordeaux.) When Robert Mondavi and Philippe de Rothschild decided to make a Bordeaux-style wine from Napa-grown grapes, they naturally used these same varieties. The red wines from Bordeaux contain one or more of several grape varieties: Cabernet sauvignon, Cabernet franc, Merlot, Malbec and Petit verdot.

Opus one 1990