Zinfandel Heritage Vineyard Update
By James A. Wolpert & Michael M. Anderson
Department of Viticulture & Enology
University of California, Davis
The assistance of UC Farm Advisors Rhonda Smith
(Sonoma), Donna Hirschfelt (Amador and El Dorado), Ed Weber (Napa),
Glenn McGourty (Mendocino), Paul Verdegaal (San Joaquin), Jack Foott
(formerly, San Luis Obispo) is gratefully acknowledged. The cooperation
of UC emeritus viticulturist Amand Kasimatis, Ridge Vineyards viticulturist
David Gates, and the departments Oakville Vineyard manager
Jason Benz, is also greatly appreciated. The Zinfandel Heritage
Vineyard is a collaboration between the Zinfandel Advocates and
Producers and the American Vineyard Foundation. The authors are
indebted to ZAPs board of directors, and in particular, to
its research committee, and its chair Joel Peterson, for their outstanding
support. We thank the American Vineyard Foundation through which
this research was funded.
Zinfandel is a grape variety of noble stature. In California, we
are fortunate that it has no historical stylistic context elsewhere
in the world that restricts our winemakers creativity.
Few New World wine regions have had the opportunity to create a
great new wine. With other varieties, we have constantly compared
our efforts to European standards. Zinfandel gives us an unparalleled
opportunity to set our own standards for unique world-class wines.
However, some winemakers have commented and even complained
for many years that the Zinfandel clones offered through
the University of Californias Foundation Plant Service (FPS)
were not high-quality selections. In short, the clones were disliked
because they had large, tight clusters and large berries, leading
to bunch rot at relatively low ripeness. The resultant wines were
criticized for having low intensity of varietal character.
Before Zinfandels country of origin was discovered, it was
not possible to improve the variety by importing better clones,
as is the case for European varieties. However, the discovery that
Croatia is the country of origin turned out to be of little help,
because the variety is not widely planted there, so the amount of
variability Croatian plant material can contribute would not be
expected to be high.
Fortunately, however, many old Zinfandel vineyards in California
survived Prohibition and often dated back to the late 1890s. The
reputation of old Zinfandel vineyards had been highlighted by winemakers,
especially since the middle and late 1980s.
Armed with these demonstrations of quality in the bottle
throughout California, and with the regional knowledge of UC farm
advisors and local vineyard managers, a concerted effort was made
to improve the UC Davis Zinfandel selections in the early 1990s.
Collecting field selections
Zinfandel selections were collected from throughout California to
increase the possibility of finding selections that distinguish
themselves. Collections were made from Sonoma, Napa, Mendocino,
Lake, Contra Costa, Alameda, Santa Clara, San Luis Obispo, San Joaquin,
Amador, El Dorado, and Calaveras counties, and the Cucamonga region
of southern California.
Selections were made from vineyards at least 60 years old and older,
because vines of this age appeared free of virus (visual red
leaf) symptoms. Attention was paid to finding vines with small
berries and no disease symptoms. In addition to preserving these
selections as a historical legacy, our goal was to choose from among
them selections for distribution that will improve the quality of
Planting the vineyard
The Zinfandel Heritage Vineyard, located in the Oakville Experimental
Vineyard (Napa Valley) currently consists of 90 selections. Phase
I, budded in 1995/96, consists of 63 selections and includes certified
selections of Zinfandel (FPS 1A, 2 and 3) as well as three selections
of Primitivo (FPS 3, 5, and 6).
In 1999, Phase II was added to the vineyard with an additional 27
selections. Dr. Carole Meredith and her associate Gerald Dangl confirmed
through DNA analysis that all the selections in Phases I and II
were indeed Zinfandel. The vineyard is planted at 9-ft x 8-ft spacing
(row x vine) on a Gravelly Bale Loam. St. George was used as the
rootstock, and the vines are head-trained and spur-pruned. Selections
in the vineyard consist of seven-vine experimental units, without
Planning for this vineyard was done with a strong appreciation that
this was both a repository of plant material and a collection of
historic material. Therefore, the vineyard was planted as traditionally
as possible. The use of St. George rootstock, nearly square spacing
and head-trained, spur-pruned vines supported only by split redwood
stakes is a design used widely 100 years ago. One concession to
modern viticulture was installation of a subsurface drip irrigation
No evaluation of the Heritage selections can be done without knowing
the status of each. Often people gather selections together and
take data, not realizing that the selections differ in viral status,
so it is impossible to know if the demonstrated differences are
due to clone or virus. The goal here was to avoid that mistake.
Relying on visual inspections, every effort was made to select vines
that were free of virus. However, tests would be needed to confirm
the viral status of the selections. All selections were tested for
grapevine fanleaf virus (GFLV) prior to budding.
Polymerase chain reaction (PCR) detection of virus in grapevines,
completed in 1999, is now felt to be more reliable than traditional
woody indexing. From this point forward, PCR will be used as the
definitive virus test for this project. Of the viruses detected
in plant material with use of PCR, grapevine leafroll (GLR) was
by far the most common, with 46% of the selections infected with
one or more of the GLR strains (data not shown).
Other detected viruses were generally found in combination with
a GLR strain. Only one selection that was free of GLR was found
to have one of the other viruses. The high number of selections
testing positive for GLR was not anticipated, reminding us once
again that the lack of red leaves in fall is far from assuring a
negative virus status.
In 1998, we began viticultural evaluations of the selections in
Phase I. These measurements are taken at harvest and include Brix,
pH, TA, berry weight, yield per vine, cluster weight, number of
clusters, and pruning weight per vine. Collection of yield-per-vine
and clusters-per-vine data began in 1999.
Table I reports mean data inclusive of all years. Yield, measured
as the mean of three vines per selection, nearly doubled from a
low of 3.5 kg to a high of 7.7 kg per vine. Mean yield was 5.0 kg
per vine. Brix values ranged from a high of 26.3† to a low of 23.2†
with the mean of 24.2†.
Average cluster weights varied almost two-fold, from 170 g to 336
g, a variation resulting from a combination of both the number of
berries per cluster and berry weight. In order for a selection to
be given advanced consideration, vines must perform uniquely and
consistently over time relative to other selections.
The Primitivo selections have their origin in Italy and therefore
may represent a line of Zinfandel different from those we collected
in California. When compared to the Heritage Vineyard selections
as a whole, several general observations can be made. Primitivo
selections (Table I) all had values of yield, cluster weight, berry
weight, and berries per cluster that were equal to or lower than
the mean for all selections. Primitivo FPS 05 had both the lightest
clusters and the smallest berries in the entire vineyard.
Additionally, the Primitivo selections had values for clusters per
vine and soluble solids that were above the vineyard mean. At this
point, the Primitivo selections, despite having more clusters per
vine, seem to have lighter yields resulting from smaller berries
and fewer berries per cluster that ripen earlier than most of the
other selections in the Heritage Vineyard.
The FPS Zinfandel selections were singled out to investigate whether
their reputation as large- berried, large-clustered, high-yielding
selections was justified. The research showed that on no parameter
did these selections set the high or low value for the vineyard.
Nor did they fall outside the range set when looking at the mean
± one standard deviation. In general, we can say that up
to this point, there is no data that distinguishes them from the
Average yield data show a clustering between 4 and 6 kg per vine
(Figure I). However, it is interesting to note that the data for
some selections are quite variable, as seen by the length of the
error bars, for example, on selections 25, 37, and 46. This means
that the yield is not consistent from year to year. Virus status
is identified with different symbols in the figure, and there is
no correlation of virus status with either yield or variability
of the data.
New replicated vineyard
As research progressed, we came to believe we would not learn all
we wanted to about the Heritage selections without a fully replicated
trial. The advantages of replication appeared to be two-fold. First,
we would have statistically valid comparisons, which would increase
our confidence when we eventually make recommendations. Second,
we would have much more fruit for winemaking trials.
One problem in our planning for a replicated vineyard was that the
large number of selections made a large vineyard impossible. So
we proceeded on a modified scale.
In 2001, a new replicated vineyard was planted. Deciding what selections
to include required constructing a logical scheme. Within the Heritage
Vineyard, there are multiple selections made from the same vineyard,
and some of the selections have been found to contain virus. Our
scheme employed these facts. Using the criteria of virus-free and
unique vineyards origin, the number of selections was reduced from
61 to 20. In the case of vineyards with multiple clean selections,
one selection was arbitrarily chosen unless wine had been made from
one of the choices previously.
The new vineyard, like the original Heritage Vineyard, is located
in the Oakville Experimental Vineyards Old Federal
vineyard. It consists of five replications of 18 vines occupying
two acres. Once again, St. George rootstock was used. The vines
are planted at a spacing of 6 x 8 and will be head-trained and spur-pruned.
It is anticipated that this vineyard will produce 450 kg (1,000
lbs) of fruit per selection, and that this will be sufficient to
produce more than one barrel of wine per selection.
The rootstock was planted in 2001 and was budded in spring 2002.
Drip irrigation was installed in 2001. This vineyard represents
a commitment to continued research on Zinfandel. The project continues
to expand the understanding of Zinfandel, and we are excited about
what will be achieved.
The range shown in growth and yield parameters thus far fuels our
hope that there is significant variability within the Zinfandel
Heritage selections. Using the Heritage Vineyard as a base, we hope
to identify Zinfandel selections that will achieve the status of
clones and play important roles in the production of Zinfandel for
years to come.