Here is what I wrote on the current mailer addressing field blends. There were many different reasons, some purposeful and some accidental.
The question of why some old vineyards in California are so diverse is one that I have been digging into for quite a while. Thanks to the librarians of northern California, who had the foresight to save obscure grape purchase receipts, as well as the inventor of graph paper, who unintentionally created the perfect paper for mapping out every vine in a vineyard, here are the main factors I believe account for field-blends.
Varietal-labeled wine was not as important: Prior to the shift to varietal labeling in the 1950s and 1960s, American winemakers and growers were more interested in making wines of a particular “style” such as “Claret” or “Burgundy” or with white, “Hock.” As such, the importance of a varieties’ character was more about what they contributed to a blend of grapes rather than about whether it was good on its own. In planting vineyards for a particular “style” of wine, vineyardists would adjust varieties based on climate, soil, etc. For instance, in hot climates where acidity and lower sugar are needed, one tends to find more Carignane, Grenache, Trousseau Noir, Mataro (Mourvedre). In cooler areas, one generally finds varieties that are earlier ripening and/or bring more color such as Petite Sirah, Alicante Bouschet, and Grand Noir.
Winemaking: Even going back to 1882, industry leaders noted the tendency of the States main “Claret” grape, Zinfandel, to have variable ripening which could cause sugars to be higher than expected in tank (we call this the “soak-up” factor today) resulting in stuck fermentations and “acetification.” To battle this, they recommended the blending of varieties that were later ripening. They were also convinced, as was considered true in Europe at the time, that blending the varieties before fermentation resulted in a better, “more harmonious” wine than one blended after fermentation. Even today we are learning, in a more scientific way, about the potency of co-fermentation and the resulting co-pigmentation, co-polymerization and the resulting stabilization of color, tannin and aromatics.
Hedging Viticultural Risk: Just as one might diversify a stock portfolio growers likely planted many different varieties in an attempt to offset potential crop loss. Vineyardists in the 1880s and 1890s were working with varieties that had little or no track record in California. On top of this, the more progressive ones were also experimenting with myriad rootstock selections whose rooting and grafting propensities were not well known. Beyond Phylloxera, there were also issues of powdery mildew and other pests.
Neighbors: As I found reading the journals of Eli T. Shepherd, who owned the present day Bedrock Vineyard in the 1880s, it was common for neighbors to buy and sell rootstock and vine cuttings from each other. Newer imports were purchased from the intrepid growers and nurserymen who foraged for vine material in Europe, but Zinfandel, Semillon, Mataro, and others already present in California were not purchased through a nursery. For instance, Shepherd went to the nursery of J.P Drummond (now Beltane Ranch in Kenwood) for St. Macaire, Beclan, and other cuttings. Drummond was also the first to import Petite Sirah into California in 1882; file this fact away for the next section, as Pagani Ranch lies across the street from Drummond’s old nursery. Similarly, H.W. Crabb, the original owner of To Kalon Vineyard in Napa, sold an array of cuttings that he had imported (his favorite being “Crabb’s Black Burgundy,” which has now been identified as Mondeuse). Our Oakville Farmhouse Vineyard, which lies catty-corner to To Kalon, is nearly 20% Mondeuse Noir. Drummond and Crabb are just two examples of how certain varieties moved outward in a diaspora like fashion from nurseries.
Randomness: Nursery stocks were not necessarily well controlled, nor were the cuttings passed between neighbors. For instance, Drummond advertised Petite Sirah, Alicante, Beclan, St. Macaire, and others that have been found in vineyards in Sonoma. But what about the random Castets vine (another of Bordeaux origin) we have found at Bedrock? My guess is that it was included in the original cuttings from France and propagated accidentally as another variety or slipped into cuttings being sold as another variety.
