Fermentation How is fermentation used to make ethanol?

Ethanol Ethanol is an important chemical with a wide variety of uses. More than tonnes of pure ethanol are produced in this country each year.

The process of making ethanol Ethanol is produced by fermentation. Yeast is added to a sugar solution and left for several days in the absence of air. These anaerobic conditions causes zymase enzymes in the yeast to convert the glucose into ethanol and carbon dioxide. But there are also other new ways to make ethanol now thanks to technology.

New ways of making ethanol There are now new ways of making alcohol other than fermentation. One way is by reacting ethene with steam, this is called hydration. The reaction is reversible which is shown by the double arrow. Only 5% of the ethene is converted into ethanol. But this isn’t a problem as the ethanol can be removed and the ethene left over can be recycled, by doing this over 95% can be converted.

New ways of making ethanol Genetically engineered E. coli bacteria could produce fuel ethanol from farm wastes such as corn stems, cobs, and leaves. A related technology can produce biodegradable plastics from biomass. This is done by genetically modifying the bacteria to produce ethanol from a waste biomass such as sugar cane, corn husks, wood and other organic matter. The biomass is mixed with the bacteria at 30-37°C and in slightly acidic conditions (ph 6.6). The ethanol produced is about 5% pure and can then be concentrated by fractional distillation.

Wine Making During the primary fermentation of wine, the two grape sugars, glucose and fructose are converted to alcohol (ethanol) by the action yeast. The by-products of primary fermentation are aromas and flavours, the gas carbon dioxide, and heat. The production of heat during fermentation means that during fermentation the temperature of the fermentation vessel will rise, and will require action on the part of the winemaker to cool it down. White fermentation is usually conducted in the range of 8-19°C, and red wine fermentations typically are allowed to run at between 25°C and 32°C. At temperatures higher than this, there can be a loss of desirable aroma and flavour. Saccharomyces cerevisiae and Saccharomyces bayanus are the bacteria that are responsible for fermentation.

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