April 2008. Wine is an alcoholic drink that is formed from the fermentation of grapes or grape juice. The word wine comes from the Latin vinum referring to both ‘wine’ and ‘vine’. Drinks that are wine-like can also be made from other fruits or from fl owers or grains.
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formed from the fermentation of
grapes or grape juice. The word wine
comes from the Latin vinum referring
to both ‘wine’ and ‘vine’. Drinks that
are wine-like can also be made from
other fruits or from fl owers or grains.
When substances other than grapes
are used to make ‘wine’, a reference
to the substance is made in the name,
for example lime wine. This is because
by itself the term ‘wine’ is defi ned
technically and legally as the beverage
derived from the fermentation of
grapes or grape juice. The word ‘wine’
by itself always means grape wine.
The earliest known evidence of a fermented wine-like drink is from the Chinese
village of Jiahu, dated from 9000 years ago (7000 BC). This rice wine was
discovered by chemically analysing the contents of sixteen buried jars.
The fi rst wine made from grapes appears to have been made between 8000
and 4500 BC during the Neolithic period in the Middle East. Various civilisations
from this time contributed to making wine popular and improving the technology
involved in the process.
In Australia, grape growing to produce wine began soon after the arrival of
European settlers, with grape vines among the cargo of the First Fleet of 1788.
Governor Phillip brought vines from Rio de Janeiro and the Cape of Good Hope
and planted them at Farm Cove in 1788.
This wine production was
largely unsuccessful due to the
lack of suitable vine types until
Gregory Blaxland (more famous
for crossing the Blue Mountains
with Lawson and Wentworth)
arrived in Sydney in 1806. He
brought a number of varieties of
vines and developed practices to
ensure the vines were resistant
to disease. Shortly afterwards,
James Busby, who had studied
viticulture in France, arrived
in New South Wales in 1824
with a collection of cuttings
and obtained a land grant of
2000 acres in the Hunter Valley.
to the spread of vine planting in Western Australia, Victoria and South Australia.
The increased immigration to Australia in the 1840s led to a rapid and successful
expansion of the industry for a variety of reasons. Some examples include:
What are the main differences?
The main differences between the composition of grape juice and wine involve
the amounts of sugar and ethanol. Compared with the starting solution of grape
juice, the wine contains far less sugar and more ethanol (alcohol).This is due
to the process of fermentation. Fermentation in wine is a process that involves a
micro-organism breaking down a molecule without using oxygen to produce energy.
The end product of fermentation is an organic molecule, in this case ethanol.
THE ROLE OF YEAST IN WINE-MAKING
The micro-organism involved in the fermentation of
grape juice to wine is yeast. Yeast is a microscopic,
single-celled fungal organism. The yeast is
responsible for providing enzymes that assist the
sugar molecules to break down. An enzyme is a
catalyst that helps a reaction take place without
undergoing permanent change in the reaction.
The yeast breaks down the sugar molecule
to obtain energy. There are many different
forms of sugars, which are collectively classed
as carbohydrates. Simple sugars, like glucose and
fructose (found in grapes), are the monomers of
more complex carbohydrates including starch
and cellulose. Glucose and fructose have the same
This image, formed by using an electron microscope, shows
a number of unicellular yeast cell
The breakdown of sugars can occur completely if oxygen is available and partially
if oxygen is unavailable. The process of breaking down an organic molecule for
energy use by an organism is respiration. Respiration with oxygen is aerobic and
without oxygen is anaerobic respiration.
The quantity of energy made available through aerobic respiration is much
greater than for respiration without oxygen. This can be seen when the energy
released is shown with the respective equations:
including yeast, are able to respire aerobically and anaerobically when insufficient
oxygen is available. For this reason they are described as facultative organisms.
When yeast respires anaerobically, the process is called fermentation and results
in the product required by wine-makers, namely ethanol.
Place 5 g of yeast in the Erlenmeyer flask. Add 10 g of sugar, then 40 mL of warm
water to the 50 mL Erlenmeyer flask. Swirl the flask to ensure the contents are mixed.
Cover the flask tightly with a balloon.
Record the circumference of the balloon when it is in position. Record the
circumference again after 5, 10, 15, 20, 25 and 30 minutes.
Fermentation, yeast and tolerance limits
An investigation into fermentation reveals the process is highly dependent on the
functioning of yeast cells. In particular, the cells play an important role due to their
The yeast has optimal temperatures and pH ranges for working. Outside of
these ranges (tolerance limits) the yeasts may die, for example if the yeasts become
too hot. This is a real problem for wine-makers as the fermentation reaction is
exothermic. This means that heat is released during the process. If the fermentation
container is insulated and heat cannot escape, the temperature will rise. If the
temperature of the fermenting juice rises above or falls below the temperature range
tolerated by yeast, then the organism will die.
Yeast will also die if the alcohol (its waste product) concentration goes over
a certain percentage. This is because the alcohol remains in the fermenting liquid.
Yeast generally can tolerate 10–15% alcohol, but some especially cultured strains
of yeast have been developed to tolerate up to 21%. The other by-product, CO2,
bubbles through the liquid and dissipates into the air.
ASSESSING THE GRAPES
Grape-growers carefully monitor their vine crop (Vitis vinifera) all year. They check
that the plants are free of pests and sample the soil. The soil and climate have a large
infl uence on the quality of the grape produced. They also help determine what type
of grape variety is selected for growth in certain areas. The soil and climate in the
Queensland Granite Belt appears to be best suited to growing white wine varieties
like chardonnay, semillon, sauvignon blanc and verdelho.
Following each harvest, vines are cut back as fl owers will develop only on new
buds. The fl owering occurs by the end of October. Pollen from the stamen (the male
part of the fl ower) transfers to the stigma (the female part) and fertilisation takes
place. During the next few months there is a period of growth where the grape
berries start to develop from the fl ower ovary. They begin as small, hard, green
berries and slowly start to soften, get bigger and take on some colour. At this stage
they contain large amounts of acid. They do not contain sugar, which is essential
for fermentation, or any fl avour.
The grape berries then start to ripen. This period is known as veraison.
The concentration of acid found in the grape berries starts to decrease and the
concentration of sugar starts to increase. The colour of the berries, due to molecules
called anthocyanins, also begins to develop and deepen, and the berries start to