Agriculture Reference
In-Depth Information
less sucrose, so that translocation of sugars to the ripening fruit is
diminished, with consequent adverse effects on quality. Conversely, N
deficiency in the fruit may lead to “stuck fermentations” and undesirable
H
2
S production during fermentation (section 5.4.1.4). The dynamics of K
uptake by vines are similar to those of N, and K has been found to attain
high concentrations in the fruit of canopies with excessive shading (i.e.,
vines out of balance). High K concentrations are associated with an
increase in the ratio of malic to tartaric acids, which leads to an increase in
pH when the young wine undergoes malo-lactic fermentation. However, K
deficiency impairs photosynthesis (and sugar production) in the leaves, and
a low K:N ratio may induce “false K deficiency” (section 5.4.3).
Summary Points
9.9
In this discussion on the relationships involving soil,
terroir
and wine character,
the following main points were made:
■
The concept of
terroir
evolved from the historical French tradition that wines of
a consistent character and quality came from particular regions, down to specific
vineyards and blocks within vineyards. This concept, widely accepted in Europe,
has not had much influence in the New World.
■
Where empirical historical evidence of a consistent association between a site and
wine quality is lacking, or deemed irrelevant, some corporate wine makers are an-
alyzing grapes at the point of delivery by rapid methods that are believed to cor-
relate with wine sensory properties. The results are used to adjust remuneration
to growers on the basis of quality.
■
Because the term
wine quality
is used in several different ways, its meaning has
become vague. With skilled wine-making techniques, it should be possible to make
quality wine from disease-free, mature fruit of any desirable variety. But the dis-
tinctive character of this wine will depend on the
terroir
(soil and climate), pro-
vided this influence is not obscured by extraneous factors in the vineyard or the
winery.
■
The scientific and technical understanding of the influence of the soil in
terroir
is
not as well advanced as that of climate, grape variety, and cultural methods. Gen-
eralizations are made about the importance of soil temperature, soil water supply,
aspect, drainage, and nutrient balance to achieve “vine balance” and good ripen-
ing conditions. But because soil is so variable in the landscape, it is likely that
quantitative relationships between soil properties and the yield and composition
of grapes will only be elucidated on a local scale (a few hectares in area). This is
consistent with the empirical evidence of the AOC system, especially as it applies
to the Grand Crus of Burgundy and the First Growths of Bordeaux. It is also con-
sistent with the concept of precision viticulture, as outlined in section 5.3.5.
■
Examples exist of a significant influence of soil on wine character for particular
grape varieties grown in St. Emilion-Pomerol, the Médoc, the Côte d'Or, Beau-
jolais, Napa Valley, and the Coonawarra Region. In these and other cases, deep-
rooted old vines that are not irrigated generally produce high quality wines of dis-
tinctive regional character.
