The Chemistry of Wine Making
The
Chemistry of Wine Making
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Who first realized
why alcohol forms from fruit?
Joseph Louis Gay-Lussac, the same scientist whose
results on combining gas volumes were explained by Avogadro, discovered the
overall reaction that converts glucose to alcohol and carbon dioxide:
C6H12O6 -->2 CO2+ 2C2H5OH
C6H12O6 -->2 CO2+ 2C2H5OH
How did Pasteur
contribute to the chemistry of winemaking?
Pasteur realized that yeast was responsible for the
conversion of glucose to alcohol. By adding yeast to a simple sugar solution,
he showed that alcohol could be formed. He also revealed that the metabolism of
yeast was pH -dependent; the acid-level played a role in determining wine's
properties. One of grapes' two principal acids, tartaric acid (malic
acid is the other), led to Pasteur's discovery
of enantiomers, molecules that are mirror images of one another. (The original
Pasteur experiment, however, has been difficult to replicate.)
Low acidity (high pH), common in grapes that are too
sweet because they were grown in excessively warm climates, lowers the amount
of subtle flavours in the grapes and consequently in the wine. As mentioned
before, there is an optimum pH for fermentation as well. Prior to fermentation,
pH is measured either by titration or more conveniently with a pH meter, and if
it is too high, tartaric acid is added.
What is the basic
composition of grapes?
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Component
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70-80
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18-25
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0.3-1.5
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20 amino acids
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0.7
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Vitamin C
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11
mg per 100 g
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73
IU per 100 g
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potassium, K+
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185
mg per 100 g
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esters
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less
than 0.1%
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13 anthocyanins
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less
than 0.1%
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What is the role of
sulfur dioxide, SO2 in wine-making?
After the grapes are crushed (the stems are
mechanically separated), the blend of pulp, skin and seeds are transfered to a
vat. (For white wine only the pulp is used). Here SO2 is introduced
to kill wild yeasts. These are too varied in composition, leading to a
competition amongst themselves that causes fermentation to stop prematurely.
They are replaced with a pure culture, usually of Saccharomyces cerevisiae
.In addition,SO2, inhibits enzymes that oxidize phenolic compounds
responsible for discolouring wine.
What role does
temperature play in wine-making
Fermentation is an exothermic process ( it releases
heat). But in wine-making, the temperature cannot exceed 85 F = 29.4 C for red
wines or 60 F = 15.3 C for white wines), otherwise the growth of yeast cells
will stop. Moreover, a lower temperature is desirable because it increases the
production of esters, other aromatic compunds and alcohol itself. This makes
the wine easier to clear and less susceptible to bacterial infection.
In general, temperature control during alcoholic fermentation is necessary to (1) facilitate yeast growth, (2) extract flavours and colours from the skins, (3) permit accumulation of desirable by-products, and (4) prevent undue rise in temperature, killing the yeast cells.
What positive role do
bacteria play in wine-making?
To clarify the wine, the fermented juice is
transfered into a settling vat, or if made on a smaller scale, into a demijohn.
In these, suspended yeast cells, cream of tartar and particles of skin and pulp
settle to the bottom of the container. As the yeast cells break down within the
precipitate, they stimulate the growth of Lactobacillus bacteria that
convert the wine's malic acid into lactic acid. This process is especially
important in wines made from highly acidic grapes because lactic acid is a weaker
acid than malic acid. (Bacteria decarboxylate malic acid , thus removing the
acidic carboxyl group), so it mellows the wine's taste.
Is the level of oxygen
important in wine making?
After the demijohn stage, the wine is repeatedly
racked to leave behind less and less precipitate. During the repeated pourings,
the wine is also given a chance to rid itself of the excess carbon dioxide from
fermentation. As the CO2 escapes, oxygen enters the wine with each
transfer, helping eventually to age the wine.
What are the benefits of resveratrol,
an antioxidant found in wine?
The Journal of Bilogical Chemistry (J. Biol. Chem.,
Nov 2005; 280: 37377 - 37382 )reported: "Several epidemiological studies
indicate that moderate consumption of wine is associated with a lower incidence
of Alzheimer's disease. Wine is enriched in antioxidant compounds with
potential neuroprotective activities. However, the exact molecular mechanisms
involved in the beneficial effects of wine intake on the neurodegenerative
process in Alzheimer's disease brain remain to be clearly defined. Here we show
that resveratrol (trans-3,4',5-trihydroxystilbene), a naturally occurring
polyphenol mainly found in grapes and red wine, markedly lowers the levels of
secreted and intracellular amyloid- (A) peptides produced from different cell
lines. Resveratrol does not inhibit A production, because it has no effect on
the A-producing enzymes - and -secretases, but promotes instead intracellular
degradation of A via a mechanism that involves the proteasome. Indeed, the
resveratrol-induced decrease of A could be prevented by several selective
proteasome inhibitors and by siRNA-directed silencing of the proteasome subunit
5. These findings demonstrate a proteasome-dependent anti-amyloidogenic
activity of resveratrol and suggest that this natural compound has a
therapeutic potential in Alzheimer's disease." For a critical look at the
potential benefits of resveratol, see this site
Wine
From Wikipedia, the free encyclopedia
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A glass of red wine.
Wine is an alcoholic beverage made from the fermented juice
of grapes.[1] Wine is defined as the product by fermentation of unmodified grape juice; their
natural chemical balance is such that grapes ferment completely without the
addition of sugars, acids, enzymes or other nutrients.[2]
Although other fruits such as apples, berries and blackcurrants are also
fermented, their wines are normally named after the fruit (for example,
"apple wine" or "elderberry wine") and are generically
known as fruit wine or country wine. Others, such as barley wine
and rice
wine (sake) are
made from starch-based materials and bear more resemblance to beers.[3]
The commercial use of the English word wine (and its equivalent in other
languages) is protected by law in many jurisdictions.
The
word wine derives from the Proto-Germanic *winam, an early
borrowing from the Latin
vinum, "wine" or "(grape) vine", itself
derived from the Proto-Indo-European stem *win-o- (cf. Ancient
Greek οῖνος oînos).[4]
Similar words for wine or grape are found in the Semitic
languages (cf. Arabic ï»ï»³ï»¦ wayn) and in Georgian
(gvino), and the term is considered an ancient wanderwort.[5]
Contents
[hide]
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[edit] History
Main article: History
of Wine
The
earliest evidence suggesting wine production comes from archaeological sites in
Georgia and Iran, dating from 6000
to 5000 BC.[6][7][8] The archaeological evidence becomes clearer, and points
to domestication of grapevine, in Early Bronze Age sites of the Near East, Sumer and Egypt from around the
third millennium BC.[9]
In Egypt,
wine became a part of recorded history, playing an important role in ancient ceremonial life.
Wine
was common in classical Greece
and Rome Western Europe
today were established by the Romans.[11] Wine making technology improved considerably during the
time of the Roman Empire . Many grape varieties
and cultivation techniques were known. Barrels were developed for storing and
shipping wine.[11]
In medieval
Europe, the Christian Church was a staunch supporter of wine
which was necessary for the celebration of the Catholic Mass. In places such as
Germany, beer
was banned and considered pagan and barbaric while wine consumption was viewed as civilized and
a sign of conversion.[12]
Production
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Wine
production by country 2005 [13]
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Rank
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Country
(with link to wine article) |
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1
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5,329,449
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2
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5,056,648
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3
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3,934,140
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4
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2,232,000
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5
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1,564,000
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6
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1,300,000
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7
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1,274,000
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8
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1,157,895
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9
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1,014,700
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10
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788,551
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11
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576,500
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Wine
grapes grow almost exclusively between thirty and fifty degrees north or south
of the equator.
The world's most southerly vineyards are in the Central
Otago region of New Zealand's South
Island near the 45th parallel,[14]
and the most northerly is in Flen, Sweden, just above the 59th parallel. [15]
Exporting
countries
The 14
largest export nations (2005 dates) – France, Italy, Spain, Australia, Chile, the United States of America, Germany, South
Africa, Portugal,
Romania, Moldova,
Hungary, Croatia and Argentina. California
produces about 90% of the wine in the United States
The
leaders in export volume by market share in 2003 were:
France,
22% 
Italy,
20% 
Spain,
16% 
Australia,
8% 
Chile,
6% 
United
States, 5% 
Portugal,
4% 
Germany,
4%
A significant volume of exports consists of "bulk wine". This is generally very basic wine which shipped to another country, and marketed there as a product of that country. The average consumer would believe it to be a product of that country's agricultural system.
[edit] Grape varieties
Wine grapes on the vine
Wine
is usually made from one or more varieties of the European species, Vitis
vinifera. When one of these varieties, such as Pinot Noir,
Chardonnay,
or Merlot, for
example, is used as the predominant grape (usually defined by law as a minimum
of 75 or 85%) the result is a varietal, as opposed to a blended wine. Blended wines are in
no way inferior to varietal wines; some of the world's most valued and
expensive wines from the Bordeaux, Rioja or Tuscany regions, are a blend of several grape varieties of
the same vintage.
Wine
can also be made from other species or from hybrids, created
by the genetic crossing of two species. Vitis
labrusca, Vitis aestivalis, Vitis muscadinia,
Vitis rupestris, Vitis rotundifolia and Vitis
riparia are native North American grapes, usually grown for eating in
fruit form or made into grape juice, jam, or jelly, but sometimes made into
wine, eg. Concord wine (Vitis labrusca species).
Hybrids
are not to be confused with the practice of grafting. Most
of the world's vineyards are planted with European vinifera vines that have
been grafted onto North American species rootstock. This is common practice
because North American grape species are resistant to phylloxera.
Grafting is done in every wine-producing country of the World except for Chile and Argentina
The
variety of grape(s), aspect (direction of slope), elevation, and topography
of the vineyard, type and chemistry of soil, the climate and seasonal
conditions under which grapes are grown, the local yeast cultures
altogether form the concept of "terroir."
The range of possibilities lead to great variety among wine products, which is
extended by the fermentation, finishing, and aging processes. Many small
producers use growing and production methods that preserve or accentuate the
aroma and taste influences of their unique terroir.[17]
However,
flavor differences are not desirable for producers of mass-market table wine
or other cheaper wines, where consistency is more important. Producers will try
to minimize differences in sources of grapes by using wine making technology
such as micro-oxygenation, tannin filtration, cross-flow
filtration, thin film evaporation, and spinning cone.[18]
Classification
A glass of white wine
Main article: Classification of wine
Wine
experts generally classify wine into categories, with the distinctions among
the classes based primarily on major differences in their manner of
vinification.
- Apéritifs (or better known as "appetizer
wines"): include dry sherry, Madeira,
Vermouth,
and other flavored wines, made to be consumed before eating a meal.
- Rosé
wines (also
called "pink wines") can be served with almost any dish,
but are considered best with seafood, salads, cold cuts, pork, and curries.
- Sparkling
wines such as champagne, are those with carbon
dioxide, either from fermentation or added later. To have this effect,
the wine is fermented twice, once in an open container to allow the carbon
dioxide to escape into the air, and a second time in a sealed container,
where the gas is caught and remains in the wine.[19] Sparkling wines that gain their carbonation from
the traditional method of bottle fermentation are called Méthode Champenoise or 'Méthode
Traditionelle'. Other international denominations of sparkling wine
include Sekt or
Schaumwein (
- Table
wines may have
an alcohol content that is no higher than 14% in the
- Dessert
wines range from
medium-sweet to very sweet. These wines are classified under dessert wines
only because they are sometimes served with desserts. Among these are port wine,
sweet
sherry, Tokaji (Tokay), Sauternes and muscatel.
- Fortified
wines are often
sweeter, and generally more alcoholic wines that have had their
fermentation process stopped by the addition of a spirit, such as brandy,
or have had additional spirit added after fermentation.[20] Brandy is a distilled
wine. Grappa
is a dry colorless brandy, distilled from fermented grape pomace, the
pulpy residue of grapes, stems and seeds that were pressed for the
winemaking process.[21]
- Cooking
wines typically
contain a significant quantity of salt. It is a wine of such poor quality,
that it is unpalatable by itself and intended for use only in cooking.
(Note, however, that most cooking authorities advise against cooking with
any wine one would find unacceptable to drink.)[22]
The
color of wine is not determined by the juice of the grape, which is almost
always clear, but rather by the presence or absence of the grape skin during
fermentation.[23] Grapes with colored juice, for example alicante
[edit] Vintages
Main article: Vintage
A vintage wine is
one made from grapes that were all, or primarily, grown in a single specified
year, and are accordingly dated as such. In the United States for a wine to be
vintage dated (and labeled with a country of origin or AVA, such as "Napa Valley"
or "New
Zealand") it must contain at least 95% of its volume from wines harvested
in that year [24]. If a wine is not labeled with a country of origin or
AVA, such as "Napa County", it must contain at least 85% of its
volume from wines harvested in that year [24]. Many wines, particularly good quality red table wines,
can improve in flavor with age if properly stored.[citation needed]
Consequently, it is not uncommon for wine enthusiasts and traders to save
bottles of an especially good vintage wine for future consumption. Most
countries allow a vintage wine to include a portion of wine that is not from
the labeled vintage. Recent research suggests vintage year may
not be as significant to wine quality as currently thought.[25]
For
some types of wine, the best-quality grapes and the most care in wine-making
are employed on vintage wines and they are therefore more expensive than
non-vintage wines. Whilst vintage wines are generally made in a single batch so
that each and every bottle will have a similar taste, climatic factors can have
a dramatic impact on the character of a wine to the extent that different
vintages from the same vineyard can vary dramatically in flavor and quality.[citation needed] Thus,
vintage wines are produced to be individually characteristic of the vintage and
to serve as the flagship wines of the producer. Non-vintage wines, however, are
blended from a number of vintages for consistency, a process which allows wine
makers to keep a reliable market image and also maintain sales even in bad
vintage years.[citation needed] Superior
vintages, from reputable producers and regions, will often fetch much higher
prices than their average vintages. Some vintage wines are only made in
better-than-average years.
Malolactic
fermentation
Malolactic
conversion is a process
of a change in wine where tart malic acid is converted to softer-tasting lactic acid.
It is
accomplished by lactic acid bacteria (such as Oenococcus
oeni) , which consume malic acid to produce energy. Depending on the
bacteria present, it can occur naturally, but in commercial wine making,
malolactic conversion typically is initiated by an inoculation
of desirable bacteria. This prevents undesirable bacterial strains from
producing off-flavors. Conversely, commercial winemakers actively prevent
malolactic conversion when it is not desired, to prevent accidential initiation
and maintain a tarter, more acidic profile in the finished wine.
Because
it consumes the malic acid, all of which is present at the time the grapes are crushed,
malolactic conversion can take place at any time during or after alcoholic fermentation. A wine undergoing
malolactic conversion will be cloudy due to the presence of bacteria, and may
have an uncanny smell of buttered popcorn, due to the production of diacetyl.
In
winemaking malolactic conversion is generally encouraged in many red wines and
some white wines, particularly those that are aged in oak. Unoaked white
wines, such as German wines generally do not undergo malolactic
conversion. Malolactic conversion tends to create a rounder, fuller mouthfeel in
subject wines by converting malic acid into lactic acid. Malic acid tastes
slightly of apples
and this can be tasted in the wine, while lactic acid is richer and more buttery.
Sometimes
malolactic conversion can occur unintentionally after the wine is bottled. This
is almost always a fault, and the result is a slightly carbonated wine that
typically tastes bad. The carbonation from this type of change should not be
confused with benign carbonation, known as spritz
Tasting
Wines
may be classified by their primary impression on the drinker's palate. They are
made up of chemical compounds which are similar or identical to those in
fruits, vegetables, and spices. The sweetness
of wine is determined by the amount of residual sugar in the wine after
fermentation, relative to the acidity present in the wine. Dry wine, for
example, has only a small amount of residual sugar.
Specific
flavors may also be sensed, due to the highly complex mix of organic molecules
such as esters and
terpenes that
grape juice and wine can contain. Tasters will also distinguish between flavors
characteristic of a specific grape (e.g., Cabernet Sauvignon and blackcurrant)
and flavors that are imparted by other factors in wine making, either
intentional or not. The most typical intentional flavor elements in wine are
those that are imparted by aging in oak casks, and virtually every element of
chocolate, vanilla, or coffee are actually a factor of oak and not the native
grape.[citation needed] Banana
flavors (isoamyl acetate) are the product of yeast
metabolism, as are spoilage aromas such as sweaty, barnyard, band-aid (4-ethylphenol
and 4-ethylguaiacol)[26],
and rotten egg (hydrogen sulfide)[27].
Wine
aroma is the result of the interaction between components of the grapes and
those produced during winemaking process, fermentation and aging.[28]
Being served at room temperature increases the vaporization of aroma compounds,
making the wine more aromatic. For some red wines that are already highly
aromatic, like Chinon
and Beaujolais,
the volatility of the wine makes it better served chilled.[29]Collecting
Château Margaux, a first
growth cult
wine from the Bordeaux region of France, is highly
collectible.
At the
highest end, rare, super-premium wines are amongst the most expensive of all
foodstuffs, and outstanding vintages from the best vineyards may sell for
thousands of dollars per bottle. The most common wines purchased for investment
include Bordeaux, cult wines
and Port.
Investment in fine wine has attracted a number of fraudsters who play on fine
wine's exclusive image and their clients' ignorance of this sector of the wine
market.[citation needed] Wine fraud
scams often work by charging excessively high prices for the wine, while
representing that it is a sound investment unaffected by economic
cycles. Like any investment, proper research is essential before investing.
False labeling is another dishonest practice commonly used.
[edit] Names
Wines
are usually named either by their grape variety or by their place of
production. Generally speaking, Old World
(European) wines are named for the place of production, with the grapes used often
not appearing on the label. New World wines (those from everywhere except Europe ) are generally named for the grape variety. More
and more, however, market recognition of particular regions and wineries is
leading to their increased prominence on New World
wine labels. Examples of recognized locales include: Napa Valley,
Barossa
Valley, Willamette Valley, Cafayate, Marlborough, Walla Walla,
etc. Still, though, the grape variety is almost invariably present on the label.
This is not the case with most European wines because of tradition and legal
restrictions.
Within
Europe, a major exception to the no-grape rule is with German wines and wines
from the Alsace region of France
Some
blended wine names are marketing terms, and the use of these names is governed
by trademark
or copyright
law, rather than a specific wine law or a patent on the actual varietal
blend or process used to achieve it.[citation needed] For example,
Meritage
(pronounced to rhyme with "heritage") is generally a Bordeaux-style
blend of Cabernet Sauvignon and Merlot, and may
also include Cabernet Franc, Petit
Verdot, and Malbec.
Use of the term Meritage is protected by licensing agreements by The Meritage
Association.
Appellations
The
taste of a wine depends not only on the grape species and varietal blend, but
also on the ground and climate (known as terroir) where it is cultivated.
Historically, wines have been known by names reflecting their origin, and
sometimes style: Bordeaux, Rioja, Mosel and Chianti are all
legally defined names, reflecting the traditional wines produced in the named
region. These naming conventions or "appellations"
(as they are known in France
The
inconsistent application of historical European designations offends many
producers there.[citation needed] For example,
in most of the world, wine labeled Champagne must be made from grapes grown in
the Champagne region of France and fermented using a certain method, based on
the international trademark agreements included in the 1919 Treaty of Versailles. However, in the
United States, there exists a legal definition called semi-generic
that enables U.S. winemakers to use certain generic terms (Champagne, Hock, Sherry, etc.) if
there appears next to the term the actual appellation of origin in order to
prevent any possible confusion [31].
Uses
Wine yearly consumption, per capita: ██ less than 1 litre. ██ from 1 to 7 litres. ██ from 7 to 15 litres. ██ from 15 to 30 litres. ██ More than 30 litres.
Wine
is a popular and important beverage that accompanies and enhances a wide range of European
and Mediterranean-style cuisines, from
the simple and traditional to the most sophisticated and complex. Red, white
and sparkling wines are the most popular, and are also known as light wines,
because they only contain approximately 10-14% alcohol. (Alcohol
percentages are usually by volume.) The apéritif
and dessert
wines contain 14-20% alcohol, and are fortified to make them richer and
sweeter than the light wines.
The
labels on certain bottles of wine suggest that they need to be set aside for an
hour before drinking to breathe, while other wines are recommended to be
drunk as soon as they are opened. Decanting is
controversial subject in wine. In addition to aeration, decanting removes some
of the bitter sediments from the bottle. Sediment is more common in older
bottles but younger wines benefit more from the aeration.[32]
During
aeration, the exposure of younger wines to air often "relaxes" the
flavors and makes them taste smoother and better integrated in aroma, texture,
and flavor. Wines that are older generally fade (lose their character and
flavor intensity) with extended aeration.[citation needed] Breathing,
however, does not benefit all wines, and should not therefore be taken to the
extreme. In general, wine should be tasted as soon as it is opened to determine
how long it may be aerated, if at all.
Religious uses
The
use of wine in religious ceremonies is common to many cultures and regions. Libations often
included wine, and the religious mysteries of Dionysus are
usually thought to have used wine as an entheogen.[citation needed] Wine plays
an integral part of Jewish laws and traditions. The Kiddush, a
blessing said before starting the first and second Shabbat or
festival meals and Havdallah, a blessing said after the Shabbat or festival
are required to be said over wine if available. On Pesach (Passover)
during the Seder, it is also required to drink four cups of wine.[33]
In the Tabernacle and in the Temple in Jerusalem, the libation of wine was part
of the sacrificial service.[citation needed]
In Christian
services wine is used in a sacred ritual called Communion or
the Eucharist,
which originates in Gospel
accounts of the Last Supper when Jesus blesses the
bread and wine and commands his followers to "do this in remembrance of
me." Wine was used in the rite by all Protestant groups until an
alternative arose in 1869
when Methodist
minister-turned-dentist Thomas Bramwell Welch applied new pasteurization
techniques to stop the natural fermentation process of grape juice.
[citation needed] Some
Christians who were part of the growing temperance movement pressed for a switch from
wine to grape juice, and there remains an ongoing debate between some American Protestant denominations as to whether wine can or
should be used in moderation for the Eucharist or for merriment. Outside the United States
[edit] Health effects
|
Red table wine
Nutritional value per 100 g |
|||||||||||
|
Energy 80 kcal 360 kJ
|
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||||||||||
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||||||||||
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10.6 g alcohol is 13 vol%.
100 g wine is 100 mL (3.4 fl oz.) Sugar and alcohol content can vary. Source: USDA Nutrient database |
|
||||||||||
The health
effects of wine (and alcohol in general) are the subject of
considerable ongoing study.[35]
In the USA France than in the USA
Some
studies have been conducted that show wine consumption can be beneficial to
health due to the presence of certain compounds. The chemical resveratrol,
which naturally occurs in grape skins, has been suggested to have anti-inflammatory,
antioxidant
and antitumor
effects, and may also protect against coronary heart diseases.[36]
As white wine has minimal contact with grape skins during vinification it
generally contains lower levels of resveratrol.[37]
Other beneficial compounds in wine include other polyphenols,
antioxidants,
and flavonoids.[38]
No
direct comparison trials have been done to determine the specific effect of
wine or other alcohol on the risk of developing heart disease or stroke.
Besides, over consumption of alcohol including wine can cause some diseases
including cirrhosis
of the liver and alcoholism.[39]
Also the American Heart Association recommends
that people not start drinking if they do not already drink alcohol just to
gain the benefits that wine provides.[40]
Packaging
Assorted wine corks
See
also: Cork (material), Alternative wine closures, and Wine bottle
Most
wines are sold in glass bottles and are sealed using a cork. Recently
there has been an increase in the number of wines being sealed with alternative
closures
