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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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Presentation Transcript
slide2

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.

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.

slide3

THE HISTORY OF 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.

slide4

New settlements around the Australian coast at this time led

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:

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GRAPE JUICE AND WINE—A COMPARISON

What are the main differences?

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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.

slide8

basicChemistry.mp3

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

formula (C6H12O6).

This image, formed by using an electron microscope, shows

a number of unicellular yeast cell

slide9

Types of respiration

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:

slide10

Humans and most other organisms respire aerobically. Some organisms,

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.

slide11

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.

slide12

sugar+alcohol.mp3

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

enzyme production.

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.

slide13

aboutGrape.mp3

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

soften.