Presentation on theme: "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."— Presentation transcript:
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.
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.
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:
GRAPE JUICE AND WINE—A COMPARISON 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 formula (C 6H12O 6 ). This image, formed by using an electron microscope, shows a number of unicellular yeast cell basicChemistry.mp3
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:
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.
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 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. sugar+alcohol.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. aboutGrape.mp3