Viniculture1...
quality factors for growing wine grapes...
The grape
vine is the source of all wine. Reaching the highest level of quality
in wine is only possible by starting with the highest quality fruit.
Maximizing fruit quality from any vineyard site can be a lengthy process,
because the end results are revealed only after several seasons of
comparison.
Grapes
are the largest fruit crop on earth2.
The grapevine prefers the temperate climate in which it evolved, with
warm, dry summers and mild winters. Winters of sustained cold kill
grapevines. High humidity promotes vine disease. Tropical temperatures
disrupt the normal vine cycle of winter dormancy.
Grapevines
are fairly adaptable plants, growing in a wide variety of soil types,
from light sand to packed clay, and flourishing around the globe in
the temperate bands between 20° and 50° Latitude, north
or south of the Equator. They are successfully grown in Europe, the
Balkans, Asia, Mediterranean and South Africa, South Australia and
New Zealand, most of North America and a good portion of South America.
THE
BEST PLANS...
There are multiple and interlacing factors to consider
when starting a vineyard, in order to ultimately achieve highest fruit
quality. In selecting a site, the average length of the ripening season,
the normal annual weather conditions, the soil type and chemistry,
fertility and drainage, the topography, sun exposure, and likely pest
problems should all be taken into account well before the first vine
is planted.
That
information will bear upon the decisions of vine variety, vine density,
row direction and spacing, irrigation and frost protection methods,
vine training system, as well as fertilization and pest control management.
These in turn will affect choices in crop load, canopy management,
harvesting, and pruning. At each step in establishing and maintaining
wine vines, the grower must evaluate and commit to a course of inevitable
compromise between highest quality and practical economy. Yet the
results of even the most carefully researched and executed decisions
are ultimately at the whim of Nature.
FAMILY TIES...
Botanical
classification puts grapevines in the Family Vitaceae, Genus
Vitis, with subgenera Euvitis and Muscadinia. Wild European grapes are Vitis sylvestris or Vitis vinifera sylvestris ("wine bearing vine of the forest"), while North America has some V. sylvestris and several additional wild non-vinifera species. There are dozens of wild and cultivated species of genus Vitis,
but only the cultivated subgenera Euvitis (true grapes),
European species vinifera, produces fine wine.
Although
there are over 10,000 documented varieties within species Vitis vinifera,
about 3,500 are cultivated, yet only about 230 or so are even regionally
significant in the world of wine and a mere dozen have been made commercially
popular and known to consumers. The study of classifying and identifying
grapevines is called ampelography.
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How
Many Bottles Grow Here?
Vineyards
vary in the spacing of the rows
and also between the individual vines.
Depending upon age and variety,
some are more productive per vine than
others, some produce larger clusters of
fruit and some yield more juice per
pound of fruit. Wine makers and their
facilities also vary in the amount of
juice they are willing or able to
squeeze from the grapes. So, in
rough averages, keeping the
variables in mind ...
| How Many ...? |
BOTTLE |
POUND |
TON |
| GRAPES per ... |
500 - 750 |
|
360 - 550 K |
| CLUSTERS per... |
2 - 25 |
1 - 9 |
2 - 18 K |
... per BOTTLE |
n/a |
±2.75 |
1/720 |
... per ACRE |
3 - 18 K |
4 - 24 K |
2 - 12 |
A Cluster averages 40-60
grapes; a Pound of grapes averages 4.5
Clusters; a Ton of
grapes averages 60 Cases wine; a Bottle of wine averages 2.75
lbs grapes.
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Vinifera
grapes are not very juicy, but have uniformly
tender pulp, easily removable seeds and
firmly-adhered skins. They also tend to be
high in acidity and lower in sugar. Properly
pruned vinifera vines develop on short stout
trunks, capable of sustaining heavy loads of
ripe fruit. More
than 90% of the world's grapes, including
those for raisins, table use, and wine, are
from this single species.
In the
subgenera Euvitis, native American vine
species include labrusca (northern fox
grape), aestivalis (summer grape),
riparia (riverbank grape),
rupestris (hillside grape) and
others3.
All these have slow-growing vines and slender
stalks, requiring trellising to support the
fruit crop. Compared with vinifera,
these species are very tolerant of cold
temperatures, but have insignificant crop
value. Only the Vitis labrusca variety Concord is
commercially important.
America
also has as native grapevines the subgenera Muscadinia,
with only two species: rotundifolia, most prevalent
throughout the Southeast, and Munsoniana, confined
to Florida. These are commonly known as "slip-skin" varieties,
for their readily-detachable skins cover juicy, somewhat tough
central pulps with firmly embedded pips (seeds). As with the
other native American grapes, their vines are also slow-growing
and weak. Muscadinia varieties have acquired natural immunity
to Pierce's
disease.
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In the
Northeastern U.S., V. labrusca grapes (Catawba, Delaware,
Niagra, etc.) are used to make wines of limited regional popularity.
Concord (V. labrusca) is almost singularly used for the commercial production of jam, jelly,
and juice, along with sweet wines that have some popularity nationally. In the Southeastern U.S., V. rotundifolia grapes
(Muscadine, Scuppernong, etc.) again make wines or primarily local
interest. Hybrid grapes (Baco Noir, Seyval Blanc, Vidal Blanc, etc.)
created from cross-pollinating European and American varieties, attempt
to gain both the flavor characteristics of the former and the weather-hardiness
of the latter, with some success.
Wine
made from native American grapes (i.e., Vitis labrusca, V. rotundifolia, etc.) is quite distinctive with
a "wild" or "foxy" flavor that tends to be an acquired taste
for most people. The essential
wine value of native American vines comes not from their grapes, but
from their roots (especially V. riparia and V. rupestris),
which are naturally resistant to the deadly louse phylloxera
vastatrix.
SEND
IN THE CLONES
Although vines could grow from the fruit seeds (or
pips), the seeds do not turn out like the either of the parents. For
example, seeds from a Chardonnay grape would not necessarily grow
into a Chardonnay vine. The grape berries that produced those seeds
began as tiny blossoms that were fertilized by the pollen of another
(not necessarily Chardonnay) vine. Like humans, the vine offspring
would carry the genetic material of both its "mother" and
"father" and share some of its parents' traits as well as
blend some of the properties into its own uniqueness.
The
Vitis vinifera vine has been very highly bred over centuries. The
modern wine vine begins as a cutting from healthy plants, so virtually
all cultivated grapevines are clones.
Vine
cuttings are called slips or scions. These are
usually grafted onto rootstock that has been specially cultivated
to combine growth vigor with resistance to disease. They are
then put into sand for one season. This is called bench-grafting. Once
the graft takes and it becomes established as part of the vine,
the scion is often refered to as the fruiting wood or bud
wood, as differentiated from the rootstock.
Some
vineyards are planted using the cultivated rootstocks directly and,
after one season to establish the root system, are then field-grafted
with the selected fruiting variety scions. With either method the
new vines are carefully nurtured to create a root system and develop
a strong, woody stalk for the first two to five years after planting,
without bearing a crop.
Young
vines with shallow root systems are particularly vulnerable to floods,
drought and fertility. If the surface soil is not too wet, too dry,
or too fertile, the roots will grow deeper and wider in search of
nourishment. Good drainage is important to establish and sustain stable,
healthy vines.
After
the roots and stalk have developed, the untended vine would grow wildly,
spending most of its energy on spreading its shoots and tendrils.
If left to nature, a single vine could cover as much as an acre of
ground, with the roots developing wherever the branches touched earth.
In ancient times, this was allowed, a practice called layering.
Normal practice of the time was to prop up the vines to prevent the
fruit from rotting or rodents from eating it. The Romans even planted
elms in the vineyards, simply to support the vines. These ancient
viticulturists came to realize that, instead of allowing the vines
to grow outward in all directions, training the vines in rows with
canes pointing upward produced better, more even-ripening grapes.
It wasn't until the recommendations of Guyot,
however, and the massive replanting due to phylloxera
that vineyards typically had an orderly, row by row appearance.
| ENEMIES
AT THE STAKES
There
are many pests and diseases that can attack and kill grape vines.
Red spiders, moth grubs and various mites, bugs and beetles
can all prey on the plant above ground. Most of these may be
controlled with either sulfur sprays, or by newer "green" methods,
such as introducing predacious insects and protective cover
crops between vine rows.
Often
the ends of vine rows are planted with a single rose bush. Insects,
mildew and fungi seem to prefer the sweet smell of roses, which
perform a "canary in a coal mine" function for grapevines,
providing early warning of the need to treat for pests or diseases.
In
climates with summer rainfall, molds such as
oidium, mildew, white rot, grey rot (see box at
left) and black rot may be prevented by regular
sprayings of a solution of copper sulfate,
slaked lime and water (Bordeaux mixture).
Research is ongoing into biological methods of
controlling these fungal problems.
New
vineyards are particularly susceptible to destruction from gophers
and moles. There are many methods of control and eradication,
including attracting predatory raptors, trapping, poisoning,
flooding and even a device that implodes burrows.
Deer,
raccoons, possums and other mammals can consume a lot of fruit,
damage more, and even harm the vines, especially young plants
and shoots. Vineyard fencing usually serves to keep these larger
animals at bay.
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Two-Faced
Fungus
Botrytis
cinerea is a fungal disease that can blight many species
of plants, including flowers, fruits, and vegetables.
Depending upon weather conditions, Botrytis can take one
of two forms in grapes, one as destroyer, the other as
enhancer.
As
"grey rot" it appears and grows during lengthy periods
of humidity early in the season. Settling in on immature
grapes, it multiplies rapidly. The bunches appear to be
covered with a grey powder and eventually darken and drop.
Yields are greatly reduced and wine made from this fruit
taste moldy and oxidizes easily. In some climates, grey
rot is a severe problem with most grape varieties.
In
certain white grape varieties, such as Semillon, Sauvignon
Blanc, Riesling, and Furmint, an infection of Botrytis
can be so beneficial, even critical to dessert wines like
French Sauternes, German Tröckenbeerenauslese, or
Hungarian Tokaj, that the mold becomes known as "Noble
Rot." Weather conditions must be right for this to occur.
Ideally, a short period of humidity or rain in mid to
late season, when the grapes are more ripe than green,
will be followed by a sustained period of cool, dry weather,
where daytime temperature hovers near 60° F.
Under
these somewhat rare conditions, the Botrytis fungi penetrate
the grape skins with mycelia to feed and take water from
the grapes, which shrivel. Overall acidity decreases.
Gums form, along with glutinic and citric acids, and the
grape sugars become very concentrated.
This
intense sweetness partially inhibits yeast and fermentation
can be very slow, lasting for months. High concentrations
of glycerol developed during these extended fermentations
and the resulting wines can be exceptionally smooth and
extremely long-lived, cellaring well for decades.
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Birds
cause the most crop loss and fruit damage, by far, in most vineyards.
All manner of controls are tried, often in combination, from timed
cannons and other noisemakers, to scarecrows and flashy streamers,
to actually covering the vines with netting.
PRUNING
FOR BALANCE
With
time, it was discovered that better-quality fruit will grow on vines
that are pruned back to distribute the bearing wood evenly over the
vine. So, in the winter months, when the leaves have dropped and the
vines are empty of sap, they are pruned back almost to the main stem.
In the Northern Hemisphere, this activity may occur anytime from November
to March depending upon the local climate and weather.
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Pruning
a head trained vine.
Just
before the beginning of warmer weather, while
the ground is often still muddy from Winter snow
and rain (note the attire), workers use pruning
knives or shears to trim back nearly all of the
previous year's vine growth.
This
photograph was taken in Sonoma County in 1942.
The practice and methods are much the same today
as they have been for centuries anywhere on
planet earth where grapes are grown for making
wine.
Photo
courtesy of Fleet
Irvine
Photomurals,
a viewable collection of wine and other theme
photos that may also be purchased.
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Pruning
is an art of delicate balance; too much will cause small, uneconomical
crops; too little will cause over-cropping and low-quality fruit.
Pruning also facilitates cultivation, disease control and harvesting,
when the vines are trained to a grow in a particular shape. It is
a skill that requires experience and judgement and cannot be done
by machine. There are only two basic pruning methods: cane-pruning
and spur-pruning, also known as head-pruning.
Spur-pruned
(head-pruned) vines are usually found in older vineyards.
Spurs are the canes (branches) trimmed back to
only a pair of buds. Each bud will become a shoot which
grows to a cane that bears the crop. In the winter after
the harvest, the top cane is removed and the bottom cane
trimmed back to a two-bud spur.
Parts
of a Grapevine
(click to
enlarge)
Spurs
are often distributed around the head of the vine, like spokes around
a wheel. The top is left open for sun-exposure and this method often
leaves the vine in somewhat of a "goblet" shape. These vineyards
can only be hand-harvested. Some head-pruned vines are converted after
a time to grow on trellis wires. Head pruning is used only in warm
growing regions, because it encourages massive vegetation that slows
ripening. It also makes harvesting more difficult.
In
the cane-pruning method, from one to four, one-year-old canes, each
with six to fourteen fruit buds, are trained along trellis wires.
This is also referred to as "cordon" (French for "arm")
pruning, since the vine looks as if it is stretching out it arms.
Because one-year-old canes must be used to bear the fruit each year,
the cane-pruners therefore must train the current fruiting canes and
at the same time consider which spurs to train for next season's fruiting
canes. In France, a single cane with a single spur is known as Guyot
simple pruning and two canes and spurs as the Double Guyot,
because Dr.
Guyot
was so influential in promoting these methods.
Modern
trellising methods vary by variety, geography, geology, harvesting
methods and winemaking style! Two, three or four-wire, vertical, lateral,
cordon and other configurations of trellis may exist in neighboring
vineyards. There are stakes made of wood, metal and those combining
the two materials. The different patterns primarily affect exposure
to sun and wind and accessibility of fruit for hand or machine harvesting.
A
VINE FOR ALL SEASONS
As Winter
ends, the pruning is nearly finished and the growers take cuttings
to make bench-grafts and root them in sand. They also begin cleaning
and repairing tractors and machines that they will be using all spring
and summer. It is also time to order Bordeaux mixture needed for spraying
as protection against mildew and other diseases and pests. As Spring
continues, the vines emerge from dormancy. Sap begins to rise and
brown sheaths, which have covered the buds, fall off. Now comes the
first working of the soil, deeply, to aerate it. 
If
the vines' bases were covered for frost-protection, they are now exposed.
The remnants of pruning are burned and any rotten vine-stakes replaced.
With
daytime temperatures starting to warm, bud-break may begin the vegetation
growth cycle as the shoots emerge. Frost danger is now at its height.
Smudge-pots, wind-machines, and frost-protection sprinklers must be
repaired and readied. The soil is worked again to keep down the weeds.
Suckers are removed from the vines about every ten days to encourage
the sap to rise in the vines. Cover crops are sometimes planted between
the rows to keep down weeds and act as hosts for predator insects.
When
the daytime temperature reaches 60-65° F, the flowering will
begin. An early flowering usually signals a very good quality vintage.
The warmer and calmer the weather, the better; rain or hail can be
disastrous now. After flowering, the shoots are thinned, the best
shoots tied to the wires. Within a few weeks, the blossoms are replaced
by minuscule berries that will grow in size, but stay green and hard.
In damp
climes, spraying with Bordeaux mixture begins midsummer. Some vineyards
pull or remove leaves from around grape clusters to improve air circulation
and reduce the possibility of bunch rot. Where weeds have been allowed
to grow between the rows, they are plowed or hoed. Long shoots trimmed
every two to three weeks to concentrate vine metabolism on the fruit.
About
mid-Summer, comes veraison, the onset of ripening as the grapes
begin to soften and swell significantly, while green varieties turn
translucent and black grape varieties gain color. This signals the
winemaker to prepare his equipment for the harvest. It is time also
for diligent bird control in the vineyards.
The grapes
now begin to sweeten as sugar is transported from the leaves into
the fruit. The berries swell from increased water content that dilutes
the concentration of the acids. Flavor compounds and tannins also
begin to build. Monitoring the grapes will soon move from weekly to
daily, anticipating harvest, as vineyard managers test sugar levels
and winemakers taste for maturity and ripeness.
DEGREES
OF QUALITY
In 1935, researchers from the University of California
at Davis began to investigate wine quality and compare climatological
history. They classified each growing area of California as a Region,
based on heat summation data. Vines are only physiologically active
above 50° F. The degree days are the total of the average
daily temperatures above this point. Grapes need at least 1700 degree
days to reach maturity. Region I is coolest at less than 2500 degree
days; Region II has from 2501 to 3000; Region III, 3001 to 3500; Region
IV, 3501 to 4000; and Region V, over 4001. This information helps
growers select appropriate varieties to match their climate.
Varieties
differ in the amount of heat required to mature their fruit. One-hundred
to 120 days after flowering, the grapes should be ripe. The harvest
may start mid-August in warm areas, to late-September in the coolest
ones.
Sugar
is measured in the U.S. using the Brix scale, which uses specific
gravity to determine the percentage of sugar, by weight. Wine grapes
are normally harvested between 19° and 25° Brix. From the
1960s through the 1980s, wineries often paid growers based on sugar
content and the tonnage.
Fruit
maturity is not, however a simple matter of sugar content. Acid content
is every bit as important to quality and flavor and even more so to
aroma constituents. Grapes will respire acid (especially malic acid)
as they ripen and this loss is greater in warmer vineyard locations.
As
grapes ripen, sugar, color and pH increase as total acidity decreases.
For the highest quality wine , grapes need to develop aroma and taste
characteristics that only result from physiological maturity and sugar-acid
balance. Some signs of this maturity are the browning of the grape
seeds (pips) and lignation, which is the browning
and drying of the berry stems. But by far the most important indicator
of maturity is the taste of the grapes.
Quality-oriented
wineries now negotiate grape purchase contracts based on acres, rather
than sugar level and tonnage. This allows the winemaker, rather than
the vineyard owner, to decide how much fruit the vines will carry
and when the grapes are ready to begin harvesting.
Picking
and the crush usually continues for two to three weeks. When
it is over, the grape skins from the wine presses are mixed with fertilizer
and spread over the vineyards. Soil may be plowed back up around the
vine-bases where necessary for protection from freezing. In the northern
hemisphere, vines are dormant from November to March. Cover-crops
may be planted between rows to help prevent erosion. As long as the
weather remains dry, any land scheduled for planting the following
spring may be deep-plowed. The vines are now immune to nearly all
harm except for an unusually severe and deep frost. When the ground
is dry and the severity of winter weather past, pruning will begin
again for the next season.
Jim
LaMar
RELATED
LINKS
The Sonoma
County Grape Growers Association run an excellent site with several
articles that provide information about growers and appellations within
Sonoma County, and grape farming issues in general.
To see a specific
application of viniculture principles and how decisions in the vineyard
apply to wine quality, see vineyard manager Marty
Mathis' page on the Kathryn Kennedy Winery
web site.
Another winery
site with general information on viniculture belongs to the Williamsburg
Winery in Virginia. They present what it takes to go from bare
ground to bottle in a very easy-to-understand manner. This is one
of the most educational winery web sites we've seen.
Wollersheim Winery
in Wisconsin has a self-paced slide show that show the progressive
stages of a vine during the first few years of establishing
a vineyard.
You may be wondering
What
Does it Cost to Produce a Glass of Wine?
- this article on the Bergman Euro-National site answers and provides
an example in great detail.
The Northwest
Berry & Grape Information Network has an online Illustrated
Guide to Field Grafting Grapevines, along
with a multitude of other general and specific viticulture information
on topics ranging from Business Management to Sustainable Agriculture.
NOTES
1While
the generally accepted word for grape farming is viticulture, raising
wine grapes has so many aspects that differ from either table grape
or raisin farming, that this new word should be adapted specifically
for wine grape farming - VINICULTURE (other cultures use it already
- try searching the web)! BACK
2Mangoes
are now the second largest crop (as recent as 2003, bananas had the
distinction - could this have been where the term "Second Banana"
originated?)! BACK
3Botanical
genus Vitis has two subgenera with distinct vine and fruit characteristics:
Euvitis (considered "true" grapes) and Muscadinia. There are less
than 60 known Vitis species. A great many of them are native to Eastern
and Southern North America, including (Euvitis) V. aestivalis, V.
amurensis, V. arizonica, V. berlandieri, V. candicans, V. champini,
V. cinerea, V. cordifolia, V. doaniana, V. labrusca (including Concord
varieties), V. lincecumii, V. monticola, V. Longii, V. riparia, V.
rufotomentosa, V. rupestris, V. solonis and (subgenera Muscadinia)
V. rotundifolia and V. Munsoniana. Only two species (Euvuitis), V.
californica and V. girdiana, are native to California. BACK
)
