“Working the Land” (Viticulture)

Viticulture: Zinfandel At-A-Glance
Vigor (low/high)
Quite productive Vigorous, so need to control leaf growth through rootstock, soil, and clone-matching, as well as --where legal – irrigation management
High quality in a wide variety of terroirs. Best to avoid vigorous, fertile soils
Yield (potential)
When left to itself, high-yield potential, so recommended to careful management, depending on vigor and winemaker intent
Growth cycle
Early budding (prone to late winter and spring frost). Mid- to late-ripening, and known to ripen unevenly within clusters
Susceptible to bunch rot in wetter/irrigate vineyards and plots and prone to magnesium deficiency and millerandage

Growing and Making Zinfandel (in California)

Zinfandel is a hearty survivor, a soldier in the field, resistant to wood-rotting diseases that kill other vines; consequently, ample amounts of century-plus Zinfandel vines are scattered throughout central and northern California. One might think that being so robust, Zinfandel would be a breeze to make. Sadly, that’s not the case. For every winemaker who laments that Pinot Noir is so finicky and challenging to make, many others specializing in Zinfandel will just chuckle! Zinfandel often ripens unevenly, leading to green grapes, fully ripe berries, and raisins -- all in the same cluster -- with flavors ranging from tart cranberry to dried black fig, sitting on a harder and at times under-ripe, frame. But with controlled yields, coupled with careful management in the vineyard and winery, the result is a Zinfandel that finds the right balance between tannins, alcohol, varietal character, and terroir: Genuine liquid joy!

Working the Land

Does soil influence the flavor of the final wine?

Traditionalists answer unequivocally “Yes!” Soil is a key element of “terroir,” the natural environment in which a vine grows, along with climate (temperature, rainfall), topography (altitude, drainage, slope, aspect) and sunlight.

A more unorthodox view holds that the influence of soil on what you taste in the glass is a myth. Maynard Amerine and Ann Noble, two famous names at UC Davis, California’s premier wine school and wine research facility, did a study on the topic. Though the study is based on Chardonnay grapes, they concluded that the following holds true for all winegrapes: “No outstanding sensory differences were observed in wines produced from different soil type locations.” The key word is “sensory” (sight, smell, taste): They are not saying that the soil doesn’t affect vine behavior (yield, growth cycle, etc.). 

The subject is most certainly up for further debate. That said, here is a brief review of how Zinfandel, according to the classic view, expresses itself in the glass based on the type of soil in which it is grown.

Alluvium/Alluvial Fans:  Each alluvial fan has its source from a single channel of run-off from the mountains, usually comprising various sizes of sediment. These soils are well-drained, and vines grown on them typically have very deep root systems. Depending on the size of the sediment, an alluvial fan will have a different degree of slope. Larger debris is sloped more steeply, but rarely more than 10 degrees. Zinfandel vines grown on benchland soils are usually healthy and produce high-quality grapes, especially as vines age, with yields, over time, naturally and increasingly restricted. 

  • California locations: Napa Valley (Rutherford Bench, Oakville), Sonoma County (Dry Creek Conglomerate, Alexander Valley), Lodi (Mokelumne River), Paso Robles (San Miguel), Santa Barbara (Happy Canyon).

Loams: Loam is a near-equal mix of silt, clay, and sand, as well as organic matter called humus, formed by the decomposition of leaves and other plant material by soil microorganisms. Loam is highly fertile and typically causes vineyards to be over-vigorous. Because of the vigor, most loam soils produce wines with little flavor and color. Despite this, loam soils offer great potential for quality wines from vineyards subject to rigorous pruning regimes.

  • California locations: There are no specific regions to call out.

Mountain/colluvial soils: Mountain fruit is often compact and concentrated, its berries tiny from seasons of struggle, and loaded with flavor due to lower yields. Accompanying thermal amplitude elongates the growing season and ripening, helping to preserve freshness and acidity -- critical for Zinfandel. 

  • California locations: Sonoma’s Moon Mountain, Sonoma Mountain, Fountaingrove; Napa Valley’s Mt. Veeder, Howell Mountain, Spring Mountain and Atlas Peak, the Santa Cruz Mountains.

Sandy: Many argue that the finest Zinfandel sites are sand-based. Due to an inhospitable microclimate where pests are concerned (the phylloxera louse does not thrive in sand), old vines thrive in such conditions and are often own-rooted (no grafting). Well-drained, yet depleted sandy soils facilitate development of deep roots. These factors, combined with the relatively small presence of loam, result in small, concentrated berries, and firm tannins. As most California Zinfandel is in Lodi, with its notably sandy soil… one can extrapolate the importance.

  • California locations: Lodi and the Delta (Oakley), Contra Costa (Oakley), and parts of the                                                                                                                                                            

Although Zinfandel is grown in 45 of California’s 58 counties, from Mendocino to Temecula and the Sierra foothills to the valleys and coastal mountains near the Pacific, its best expressions are concentrated in Napa Valley, Lodi, Paso Robles, the Sierra foothills, and the counties of Mendocino, Contra Costa, and, especially, Sonoma. More than any other variety, Zinfandel delivers “history in a glass.” Zinfandel’s association with old-vine vineyards across the state prompts the question: “Are the vines old because the vineyards are good, or are the vines good because the vineyards are old?” The truth is likely somewhere in the middle. California’s 100+ year-old Zinfandel vineyards are vinous treasures, yielding some of the world’s most distinctive wines, made in small quantities, with limited distribution. Many are field blends, including other grapes such as Carignan, Alicante Bouschet and Petite Sirah, primarily head-pruned and dry-farmed, producing wines that are unique and intensely flavored. 

Officially, there are some 39, (including three provisional) Zinfandel clones authorized at UC Davis. Before 1990, UC Davis offered only four certified Zinfandel clones (FPS 01A, 02, 03, 06). This relative lack of clones was due in part to the genetic stability of the grape, but also to an absence of interest on the part of growers and researchers. Subsequently, in the mid-1990s, with support and guidance from ZAP, the UC Davis Zinfandel Heritage Vineyard Project was birthed, with the purpose of identifying new, high-quality clones from old Zinfandel vineyards. UC Davis’ Jim Wolpert collected about 90 different Zinfandel selections from old vines (60+ years) with smallish berries and loose clusters and planted them, head-trained, 9’ x 8’ spacing, on St. George rootstock at the UC Davis Oakville station. This number was later reduced to about 20 virus-free selections, and in 2009, the UC Davis Foundation Plant Services released 19 of them.

For more on Zinfandel clones created in California, check out UC Davis’ Foundation Plant Services: Grapes.

Trellising– perhaps no topic is as widely debated among Zinfandel growers as trellising. Head-trained, old-vine Zinfandel can differ greatly from younger Zinfandel vines trained on vertical trellises. Many growers favor old bush vines with naturally low yields, somewhat thicker skins, deep roots that help contend with hot dry weather, and enough shade to protect grapes from desiccation. Others advocate vertical trellising, arguing that it provides more uniform exposure to sunlight, facilitating improved air flow, reducing the risk of rot, and contributing to a more even ripening of the berries, thus minimizing raisining with its associated overripe flavors and harsh tannins.

Zinfandel’s vulnerability to rot requires good ventilation, so drying breezes are essential. Though most newer Zinfandel vineyards are irrigated, California’s old-vine Zinfandels were dry-farmed, so adequate winter rainfall, as in Russian River Valley and/or a high-water table as in Lodi, was essential in the past. Dry farming also requires that vines be planted with wide spacing (10’ x 10’ or similar) to allow for scarce access to H2O. 

Old vine Zinfandel is almost all either self-rooted or grafted to St. George (vitis rupestris) rootstock, which was popular and widely available during post-phylloxera re-plantings in the late 19th and early 20th centuries. There’s also an advantage to using a rootstock where viral interactions between the grape variety and rootstock are already known. St. George’s exceptionally deep rooting system helps in drought-prone areas where much of California’s Zinfandel is planted. For more on Zinfandel viticulture, visit Lodi Growers “Optimizing Zinfandel for Red Wine Production.” 

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Sustainability and California

As an agricultural industry, the California wine community has a long history of adapting to change and demonstrating its commitment to sound environmental practices and social responsibility. Building on these efforts are the educational and certification programs of the California Sustainable Winegrowing Alliance (CSWA). Established by Wine Institute and the California Association of Winegrape Growers, CSWA is the most comprehensive and widely adopted wine sustainability program in the world, and– together with other important sustainability programs in regions throughout the state– has made California wine a leader in addressing climate change.