One of the questions I’ve begun to think about as I start the research for my book on Cabernet Sauvignon is whether the traditional difference between blended wines in Bordeaux but varietal wines in Napa is still justified.

Blending in Bordeaux originated as a protection against failure of any one variety in a climate that was marginal (at least for the varieties being grown). Cabernet Sauvignon did not ripen reliably every year on the left bank, so blending with varieties that ripened more easily (originally with Malbec, later with Merlot) offered two advantages: adding riper flavors to the wine than would be obtained with Cabernet Sauvignon alone; and being able to vary the composition of the blend to respond to failures and successes each year. It also allowed more vineyard area to be cultivated, since Merlot will ripen in spots where Cabernet is not successful. (On the right bank, of course, Cabernet Sauvignon is even harder to ripen and so is generally replaced by Cabernet Franc, but the same principle applies). Even today, with warmer vintages and better viticulture, there is still significant variation in annual usage of each variety; Chateau Palmer, for example, has varied from 40% Cabernet Sauvignon to 68% in the first decade of this century.

The contrasting focus on monovarietal wine in Napa Valley comes partly from the move to varietal labeling that was stimulated by Frank Schoonmaker after the second world war, and which became standard in the New World. (Before then, most wines were labeled by reference to Europe with generic names such as Claret or Burgundy.) Of course, at first the situation in California was not in fact too different from that in Europe, because the rules were so lax that a wine could be labeled with a varietal name so long as it had more than 50% of the variety. Slowly the rules became tightened until reaching today’s minimum limit of 75%. The rationale for making monovarietal Cabernet Sauvignon is that the grapes ripen more reliably in Napa than they did in Bordeaux, the result being that the mid palate is full of fruit, and does not need to be filled in by Merlot or other varieties. Proponents of monovarietals would argue that Cabernet Sauvignon achieves a full flavor spectrum in Napa without needing assistance from other varieties, in fact, I suppose they might take this argument to the logical conclusion of saying that you can only really appreciate the full varietal force of Cabernet Sauvignon if you don’t weaken it with other varieties.

But do these arguments for a fundamental difference in approach still hold up? In the past two decades, climate change has seen temperatures in Bordeaux warm to basically those that Napa showed in the 1970s. Napa has also warmed up a bit, but the gap has narrowed. Climate change has caused somewhat of a change in attitude to winemaking. One of the themes of my book is that prior to 1982, the issue in Bordeaux was trying to get Cabernet to ripeness; the issue in Napa was taming the ripeness to achieve a Bordeaux-like elegancy. Post 1982, a change in consumer attitudes meant that riper, fuller wines were desirable – no more of that touch of herbaceousness that characterized traditional Bordeaux. Coupled with the move to picking on “phenolic ripeness” rather than sugar levels, this led to increasing alcohol levels in the wines. Now the problem everywhere is to control the ripeness. It’s still true that Napa reaches greater ripeness than Bordeaux, typically resulting in an extra per cent of alcohol.

Is it the case that this extra ripeness means that Cabernet Sauvignon is complete in itself or is it true rather that blending even with small amounts of other varieties increases complexity? Should the Bordelais reconsider their view that monovarietal Cabernet Sauvignon is uncouth; or should the Napa producers move to blending in at least a little Merlot to add variety? Before trying to answer this question, it seems to me that the basic facts need to be established. After all, wines labeled as Cabernet Sauvignon in Napa can have up to 25% of other varieties, and even small amounts of secondary varieties can have a significant effect on taste. I remember a blending exercise we did on a Master of Wine trip to Bordeaux where it was surprising what a difference it made to the feeling of completeness in the overall blend when just a tiny percentage of Petit Verdot was included. The question is whether in comparing Bordeaux and Napa we are comparing blended wine with monovarietal wine, or whether we are comparing wines blended with a smaller overall proportion of Cabernet Sauvignon with wines blended with a greater proportion.  So I propose to begin by trying to establish the constitution of wines that are varietal-labeled by determining just how many are really 100% Cabernet and how many have a minor component of another variety. That should be the starting point for an investigation of whether the best wines will be made by blending in Bordeaux but not in Napa. Of course, the answer might depend to some extent on the criteria: mine will be for complexity and elegance in the wine.

In the Médoc, there is a de facto association between quality and Cabernet Sauvignon. The first growths have higher average levels of Cabernet Sauvignon than the second growths, the other grand cru classés are lower, and cru bourgeois are lower yet. (Some of the top wines have more than the 75% Cabernet Sauvignon that would be required for them to be labeled as varietals in Napa!) Whether this is due to the fact that the first growths have better terroir (that is, more reliably capable of ripening Cabernet Sauvignon) or is due to more commercial factors is hard to say, but the fact is that there’s a correlation (albeit rather a loose one) between proportion of Cabernet Sauvignon and position in the marketplace. What does this tell us about Napa, where the majority of wines have more than 75% Cabernet Sauvignon (that is, are varietal-labeled), although they do not necessarily show a price advantage over other Cabernet-based wines. Some of the most expensive cult wines are labeled as Cabernet Sauvignon, others as Proprietary Red. (Of course, whether the varietal-labeled wines are monovarietal remains to be seen.) Cabernet-based wines are certainly at the top of Napa’s hierarchy, but they don’t have to be varietal-labeled.

Which leads me to another thought. The difference between wines of the Médoc and Napa Valley has narrowed since the turning point of 1982. There is a convergence on what is sometimes called the “international” style, focusing on fruits. Partly this is due to Bordeaux closing the temperature gap with Napa, partly it is due to adoption of shared attitudes on viticulture and vinification. (Also notable is the fact that Bordeaux has increasingly moved in the direction of Merlot to obtain those richer flavors: plantings of Cabernet Sauvignon in Bordeaux peaked at 32% in 1990 but today are only 24%, although the Médoc remains around 60%.) It is definitely more difficult to be confident of distinguishing the wines in blind tastings. So to what extent are the differences due to the focus on blending in Bordeaux as opposed to varietal focus in Napa? Would the answer become clear from a comparative tasting of Meritage wines (Bordeaux-like blends from Napa) against Napa or Bordeaux? And of course back to the basic question: what makes the best wine?