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By Da Beattie

Fermentation is a widely used process that creates the air in yeasted breads and the carbonation in alcoholic beverages. The source is yeast.

Yeast is a microorganism that is is eukaryotic and single celled. Humans are also eukaryotic meaning that their cells, or in the case of yeast, singular cell, has a nucleus that holds DNA and other membrane bound organelles such as the mitochondria. Prokaryotes on the other hand, store their DNA in a nucleoid which ice not membrane bound and they do not have mitochondria. Although they are also eukaryotic in domain, at the kingdom level (the second highest taxonomic rank) yeast diverse from humans which are animals and yeast is fungus.

Yeast fermentation is the process in which sugars are metabolized to carbon dioxide and alcohol in the absence of oxygen. In the presence of oxygen, yeast convert sugars to carbon dioxide and water.

Fermentation was discovered in 1815 when French chemist Joseph Louis Gay Lussac discovered that in the absence of yeast, grape juice wort remained unfermented. However, it was another French chemist Louis Pasteur who solidified the role of yeast in fermentation.

The first step of fermentation is glycolysis which converts glucose to pyruvate, a process all living cells can do. With oxygen present, pyruvate can go on to many more cycles of metabolism like the tricarboxylic acid cycle and eventually the electron transport chain. In the absence of oxygen, pyruvate can be converted to ethanol or lactate.

The process of fermentation has been used and exploited in many diverse ways. Different strains of yeast can survive higher alcohol contents before cell death and this can be used to create the array of alcoholic beverages on the market today. Beer is made from fermenting malted barley. Wine is from fermenting fruits which are most commonly but not exclusively grapes. Mead is created by fermenting honey. Sake is from fermented rice. Gin is distilled and flavoured with Juniper berries. Brandy is distilled wine from grapes. Whiskey is from grain which can be barley, rye, wheat, or corn. Rum is from sugarcane and vodka is distilled from potatoes, grains or fruit.


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