Introduction:

Winemaking (also wine making) or vinification is the production of wine, starting with
the selection of the fruit, its fermentation into alcohol, and the bottling of the finished
liquid.
Winemaking can be divided into two general categories: still wine production (without
carbonation) and sparkling wine production (with carbonation – natural or injected).
Red wine, white wine, and rosé are the other main categories. Although most wine is
made from grapes, it may also be made from other plants.
Winemaking process:
Although there are many different methods and variations involved in winemaking,
there are seven essential steps that must be taken. These seven steps include
harvesting, de-stemming, crushing, fermentation, malolactic fermentation,
clarification, and bottling.
1.Harvesting
Harvesting or picking is certainly the first step in the actual wine making process.
Without fruit there would be no wine, and no fruit other than grapes can produce
annually a reliable amount of sugar to yield sufficient alcohol to preserve the resulting
beverage, nor have other fruits the requisite acids, esters and tannins to make natural,
stable wine on a consistent basis.
However ,the moment the grapes are picked is a big deal. Picking earlier will produce
wines with higher acidity, lower alcohol, and sometimes more green or herbal flavors.
It could also lend to more bitter tannin but the wines tend to age longer. Picking later
in the harvest season will produce wines with lower acidity, higher alcohol (or
sweetness), and riper tannin.
When picked too late some wines must be artificially acidified in order not to taste
flabby. Additionally, some will have water added to them (called ‘watering back’) to
reduce the alcohol concentration in the completed wine.
Besides picking the grapes at the moment when acidity level and sweetness are
perfectly in balance there’s also a weather problem. Every vintage is different.
Sometimes weather takes a turn for the worse at the end of the growing season and can
even result in a bad vintage.
In a situation where rains are forecasted in cooler climate areas some winemakers
choose to hedge their bets and pick grapes before optimal ripeness.
2.De-stemming
The objective of separating the grapes from the branches and/or leaves is mainly
because they provide flavors and aromas that are bitter for the wine during maceration
3.Crushing and Pressing
Crushing the whole clusters of fresh ripe grapes is traditionally the next step in the
wine making process. Today, mechanical crushers perform the time-honored tradition
of stomping or trodding the grapes into what is commonly referred to as must. For
thousands of years, it was men and women who performed the harvest dance in barrels
and presses that began grape juice's magical transformation from concentrated sunlight
and water held together in clusters of fruit to the most healthful and mystical of all
beverages - wine. As with anything in life, change involves something lost and
something gained. By using mechanical presses, much of the romance and ritual has
departed this stage of wine making, but one need not lament too long due to the
immense sanitary gain that mechanical pressing brings to wine making. Mechanical
pressing has also improved the quality and longevity of wine, while reducing the
winemaker's need for preservatives. Having said all this, it is important to note that not
all wine begins life in a crusher. Sometimes, winemakers choose to allow fermentation
to begin inside uncrushed whole grape clusters, allowing the natural weight of the
grapes and the onset of fermentation to burst the skins of the grapes before pressing
the uncrushed clusters.

Up until crushing and pressing the steps for making white wine and red wine are
essentially the same. However, if a winemaker is to make white wine, he or she will
quickly press the must after crushing in order to separate the juice from the skins,
seeds, and solids. By doing so unwanted color (which comes from the skin of the
grape, not the juice) and tannins cannot leach into the white wine. Essentially, white
wine is allowed very little skin contact, while red wine is left in contact with its skins
to garner color, flavor, and additional tannins during fermentation, which of course is
the next step.
4.Fermentation
Fermentation is a natural process in which the grape sugars (mostly glucose and
fructose) are transformed into ethyl alcohol and carbon dioxide gas by wine yeasts as
Saccharomyces cerevisiae (vini, var elipsoideus). In 1810, The French chemist and
physicist Joseph-Louis Gay-Lussac described this process in the following chemical
equation:
C6H12O6 → 2 C2H5OH + 2 CO2
Today we know that wine fermentation is carried out by certain enzymes that act as
catalysts in facilitating the fermentable sugars to alcohol/CO2 conversion. The
fermentation process closely parallels the glycolysis cycle which is elementary to
modern biochemistry and that heat energy is also a product of the transformation. Thus
the original Gay-Lussac equation is modified as follows:
C6H12O6 → 2 C2H5OH + 2 CO2 + 56 kcal of energy
Yeast enzyme
Pasteur’s work even though he did not clearly understand the nature of the process,
established the essential validity of the Gay-Lucsac equation but also showed that a
variety.
Of by-products were present which were not accounted for by the equation. Among the
common by-products are glycerol, acetic and lactic acids, and acetaldehyde…
The yield of alcohol is of great practical importance to the winemaker. It is obvious
that this is biologically unobtainable and in practice will depend on a variety of
factors.
Amount of by-products, amount of sugars used by yeasts, sugars used by other
microorganisms, alcohol loss by evaporation, the temperature, the rate of fermentation,
presence of air, stirring as another movement of fermenting mass, and other factors.
Fermentation is indeed the magic at play in the making of wine. If left to its own
devices must or juice will begin fermenting naturally within 6-12 hours with the aid of
wild yeasts in the air. In very clean, well-established wineries and vineyards this
natural fermentation is a welcome phenomenon. However, for a variety of reasons,
many winemakers prefer to intervene at this stage by inoculating the natural must. This
means they will kill the wild and sometimes unpredictable natural yeasts and then
introduce a strain of yeast of personal choosing in order to more readily predict the end
result. Regardless of the chosen path, once fermentation begins, it normally continues
until all of the sugar is converted to alcohol and a dry wine is produced. Fermentation
can require anywhere from ten days to a month or more. The resulting level of alcohol
in a wine will vary from one locale to the next, due to the total sugar content of the
must. An alcohol level of 10% in cool climates versus a high of 15% in warmer areas
is considered normal. Sweet wine is produced when the fermentation process stops
before all of the sugar has been converted into alcohol.
5.Malolactic fermentation
Put simply malolactic fermentation or MLF is the conversion of malic acid into lactic
acid within a must or wine. It’s a common – and in some styles necessary – step which
takes place in the winery and is facilitated by lactic bacteria. Most cultures of
malolactic bacteria are found in the Leuconostoc and Lactobacillus species and
Pediococcus strains.
The process ‘softens’ the acidity of wines through the conversion of harsh-tasting
malic acid into softer lactic acid, and it also raises the pH of the wine. The bacteria can
be introduced to the wine via inoculation during or after alcoholic fermentation, but in
many wineries the bacteria is present in the cellar so spontaneous MLF can occur.

The bacteria like to operate in a warm environment (+16 degrees Celsius) and
traditionally this meant winemakers had to wait until the spring following the harvest
for the malolactic fermentation to occur.

However, modern cellars and tanks can be heated up to allow the malolactic
fermentation to start as soon as desired.
The process, which is technically a bacterial conversion rather than a fermentation
because it doesn’t use yeast, also helps to stabilise the wine by preventing it from
going through spontaneous MLF later, potentially after bottling.

6.Clarification

Once fermentation is completed, the clarification process begins. Winemakers have the
option of racking or siphoning their wines from one tank or barrel to the next in the
hope of leaving the precipitates and solids called pomace in the bottom of the
fermenting tank. Filtering and fining may also be done at this stage. Filtration can be
done with everything from a course filter that catches only large solids to a sterile filter
pad that strips wine of all life. Fining occurs when substances are added to a wine to
clarify them. Often, winemakers will add egg whites, clay, or other compounds to
wine that will help precipitate dead yeast cells and other solids out of a wine. These
substances adhere to the unwanted solids and force them to the bottom of the tank. The
clarified wine is then racked into another vessel, where it is ready for bottling or
further aging.

7.Aging / Bottling

Once clarification has finished, the wine can be bottled right away or can undergo
additional aging.Yeasts have transformed sugar into alcohol and they have created
secondary aromas during fermentation. However, wine is still immature and needs to
grow and rest to harmonize aromas. It is the time that allows the wine to adjust its
sharpness and to balance acidity and tannins. The period between the end of
fermentation and bottling is called wine maturation.

For the wine maturation, it is very important the way the wine is kept (storage rooms,
control of humidity, temperature, and light) especially the choice of the container.
Three common vessels are used in this phase: Stainless Steel or Concrete and Oak.

 Stainless Steel or Concrete

These vessels do not add any flavors to the wine and can be used for both storage and
maturation.

Oxygen can have a negative impact on wine. To prevent that, these vessels can be
made airtight.

 Oak

Oak or Barrell adds tertiary flavors to the wine and allows the wine to evolve as it
interacts with a limited amount of oxygen during the maturation.

The size, the age, the contact length, and the heat applied to the barrel, are all factors
that will determine the tertiary flavors of the wine.
These can vary from vanilla, tobacco, cocoa, and spice.

Oxygen plays a role too as the barrels are not airtight.

The oxygen helps soften the tannins and can be responsible for flavors like nuts,
caramel, and dry fruit.

Winemakers can find an abundance of literature relating to the compositions of oak

Conclusion

The process of winemaking has existed for around 7,000 years, but only in the last 150
years has the science behind it been understood. Engineers and scientists have since
improved the process by making it more consistent and efficient, but there is still much
about wine making that remains elusive. Taste is very subjective, making it nearly
impossible to predict exactly how a consumer will react to a certain bottle of wine.
There is no doubt that winemakers and scientists have greatly contributed their
expertise to the process, but there is still more to be discovered about the art and
science of winemaking.