Two
parts form a grape bunch: the stem constitutes the body
and the berries composed of skin, pulp and pip.
STEM
It constitutes about 3 to 5 % of the grape weight. It
is rich in water, minerals and contains tannin that
can impart to the wine a certain pungency (stem taste)
and a grassy taste. This is why, based on the variety
and the type of wine made, the berries are de-stemmed.
PULP
In quantity, with 80 % of the weight of a grape bunch,
this is the most important part. Colourless, it is composed
of water, sugar (glucose + fructose), and 3 main acids
(tartaric, malic, citric), minerals, especially potassium,
and nitrogenised substances, main source of food for
yeast. It also contains enzymes and vitamins.
SKIN
It represents 10 % of the weight of the bunch. It is
covered by a thin waxy white coat called "pruine", on
which the necessary yeast are deposited to convert the
grape juice into wine. The skin is rich in tannin and
colouring matters; this is what colours the wine. Lastly,
some aromatic substances, specific to each variety,
are present in the skin in the form of aroma precursors.
PIPS
There can be 2, 3 or 4 pips per berry, which constitute
4 to 5 % of the bunch weight. They are rich in tannin
and oily substances (lipids).
It
is the main phase of winemaking. Since Pasteur, we know
that alcoholic fermentation is a natural microbiologic
process during which grape sugars are transformed into
alcohol under the action of yeast.
This
transformation is accompanied by carbon dioxide release,
and the must (fermenting grape juice) temperature increases.
The temperature must be controlled at this stage or
the yeast could stop working, even die, therefore stopping
fermentation, if there are too many tempreature changes.
It could have disastrous consequences, especially if
sugars remain in the must because microorganisms other
than yeast could attack them. Lactic bacteria will produce
with these sugars acetic acid, also known as vinegar.
Cooling the must now prevents this accident, which was
frequent in the past.
Fermentation
is done when all the sugars in the juice are consumed.
There is a direct correlation between the sugar content
of grapes and the alcoholic degree of a wine. On average,
yeasts consume 17,5 grams of sugar per litre to form
one degree of alcohol.
Though alcohol is quantitatively the main element transformed,
the other yeast synthesised substances or substances
present in the grape berries have an utmost importance
in the quality and typicality of a wine. These substances
are mainly aromatic components, tannins, colouring matters,
acids.
This
is also called "second fermentation" and is the process
that transforms malic acid into lactic acid. This transformation
causes the acidity of a wine to drop (malic acid is
a stronger acid than lactic acid), but increases the
stability of a wine.
Ok,so
what is Malic acid? It is a natural organic acid which
occurs in a lot of fruits and vegetables. It is very
beneficial as it is a key input in mitochondrial functions
and since it helps in boosting energy production, it
is used commonly in the treatment of chronic fatigue.
It is found in greatest quantities in apples. The old
adage an apple a day keeps the doctor away may be reflective
of the energy boosting qualities of Malic Acid.
Because
it encourages suppleness in wines, malolactic fermentation
is always favoured in red wines. Because it reduces
the acidity of a wine, it is not always encouraged in
white wines.
This
other technique consists in depositing whole grapes,
neither crushed nor de-stemmed, in a carbon dioxide
enriched atmosphere. An intracellular fermentation then
occurs, inside the grape, under the action of enzymes
that transform a small quantity of sugar in alcohol
(in the order of 2 % per vol.). There is also production
of carbon dioxide, a little glycerol and various secondary
products. The winemaker will also notice some diffusion
of aromatic substances from the inside of the grape
skin, where aromas of red berries and English candy
appear. After this maceration phase, the grapes are
then pressed, and the alcoholic fermentation happens
normally. When maceration is of short duration, wines
obtained are supple and smooth (eg. Beaujolais). On
the contrary, a longer maceration between 10 to 20 days
can produce wines for ageing; this technique is widespread
in Languedoc-Roussillon and in the Southern Côtes du
Rhône.
In
1863, an unwanted passenger was carried from the US
into Europe. This was Dactylasphaera vitifoliae,
or phylloxera, a small, yellow louse, which feeds
on the roots of grape vines. Once the winemakers realized
their vines were failing, they formed commissions to
figure out why. Even when findings were published pointing
blame at the louse, winemakers and the public were slow
to believe it. They figured it was the weather, overproduction,
overpruning, or bad soil. When France lost almost 75%
of its vines, the government began to take the louse
seriously. The answer to the problem came in the realization
that American rootstock had long since developed a resistance
to this louse. The European vines needed to be grafted
onto American rootstock.
Terroir
:
You'll
keep running into this word. Very broadly, this
means the soil, the microclimate and everything
about it that makes a particular vineyard distinct.
In short it is the soul of the land and it is
this, which finds its final expression in the
grape that grows on that patch of land.
Ask
a Frenchman to talk about this, to know what we
mean. Bruno Yvon of Clicquot Asia spoke for half
an hour without pausing for breath when we asked
him. This also reflects a profound difference
in the philosophy of winemaking between the Old
World winemakers and the New world winemakers.
In Australia and the US, they believe that it
is a science and the focus is more on the process
of winemaking and stuff like clonal selection
of grapes, pH levels, refractometers to check
sugar levels and so on .
