Fermentation

Louis Pasteur

Fermentation [fur-men-tey-shuhn] is when a living cell uses sugar for energy without requiring oxygen. Yeast is an organism that ferments. When yeast ferments sugar, the yeast eats sugar and makes alcohol. Other organisms (such as bacteria) make vinegar (acetic acid) or lactic acid when they ferment sugar. Fermentation is used to make beer, some types of fuel, and to make bread rise. When yeast ferments, it breaks down the glucose into ethanol and carbon dioxide.

Ethanol fermentation always produces ethanol and carbon dioxide. It is important in bread-making, brewing, and winemaking. Lactic acid fermentation produces lactic acid. It happens in muscles of animals when they need lots of energy fast, and is also used to preserve foods in pickling. The word ‘fermentation’ is derived from the Latin verb ‘fervere,’ which means ‘to boil’ (same root as ‘effervescence’). It is thought to have been first used in the late fourteenth century in alchemy, but only in a broad sense. It was not used in the modern scientific sense until around 1600.

The first solid evidence of the living nature of yeast appeared between 1837 and 1838 when three scientists each independently concluded as a result of microscopic investigations that yeast is a living organism that reproduces by budding. Soon, bacteria were also discovered. The term ‘fermentation’ was first used in English in the late 1840s, but it did not come into general use until the 1870s, and then largely in connection with the new ‘germ theory of disease.’ In 1857, Pasteur showed that lactic acid fermentation is caused by living organisms. In 1860, he demonstrated that bacteria cause souring in milk, a process formerly thought to be merely a chemical change, and his work in identifying the role of microorganisms in food spoilage led to the process of pasteurization. In 1877, working to improve the French brewing industry, Pasteur published his famous paper on fermentation, ‘Etudes sur la Bière,’ which was translated into English in 1879 as ‘Studies on Fermentation.’ He defined fermentation (incorrectly) as ‘Life without air.’ Though, even in the presence of abundant oxygen, yeast cells greatly prefer fermentation to oxidative phosphorylation, as long as sugars are readily available for consumption. The antibiotic activity of hops also inhibits aerobic metabolism in yeast.

Although showing fermentation to be the result of the action of living microorganisms was a breakthrough, it did not explain the basic nature of the fermentation process, or prove that it is caused by the microorganisms that appear to be always present. Many scientists, including Pasteur, had unsuccessfully attempted to extract the fermentation enzyme from yeast. Success came in 1897 when the German chemist Eduard Buechner ground up yeast, extracted a juice from them, then found to his amazement that this ‘dead’ liquid would ferment a sugar solution, forming carbon dioxide and alcohol much like living yeasts. The ‘unorganized ferments’ behaved just like the organized ones. From that time on, the term ‘enzyme’ came to be applied to all ferments. It was then understood that fermentation is caused by enzymes that are produced by microorganisms. In 1907, Buechner won the Nobel Prize in chemistry for his work. Advances in microbiology and fermentation technology have continued steadily up until the present. For example, in the late 1970s, it was discovered that microorganisms could be mutated with physical and chemical treatments to be higher-yielding, faster-growing, tolerant of less oxygen, and able to use a more concentrated medium. Strain selection and hybridization developed as well, affecting most modern food fermentations.

Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol. The science of fermentation is also known as, zymology or zymurgy. Fermentation usually implies that the action of microorganisms is desirable, and the process is used to produce alcoholic beverages such as wine, beer, and cider. Fermentation also is employed in the leavening of bread (carbondioxide produced by yeast activity); in preservation techniques to produce lactic acid in sour foods such as sauerkraut, dry sausages, kimchi, and yogurt; and in pickling of foods with vinegar (acetic acid).

Natural fermentation precedes human history. Since ancient times, however, humans have been controlling the fermentation process. The earliest evidence of winemaking dates from eight thousand years ago, in Georgia, in the Caucasus area. Seven-thousand-year-old jars containing the remains of wine have been excavated in the Zagros Mountains in Iran, which are now on display at the University of Pennsylvania. There is strong evidence that people were fermenting beverages in Babylon circa 3000 BCE. The primary benefit of fermentation is the conversion of sugars and other carbohydrates, e.g., converting juice into wine, grains into beer, carbohydrates into carbon dioxide to leaven bread, and sugars in vegetables into preservative organic acids.

Food fermentation has been said to serve five main purposes: Enrichment of the diet through development of a diversity of flavors, aromas, and textures in food substrates; Preservation of substantial amounts of food through lactic acid, alcohol, acetic acid, and alkaline fermentations; Biological enrichment of food substrates with protein, essential amino acids, essential fatty acids, and vitamins; Elimination of antinutrients (compounds that interfere with the absorption of nutrients); and a decrease in cooking time and fuel requirement.

Alaska has witnessed a steady increase of cases of botulism since 1985. It has more cases of botulism than any other state in the US. This is caused by the traditional Eskimo practice of allowing animal products such as whole fish, fish heads, walrus, sea lion, and whale flippers, beaver tails, seal oil, birds, etc., to ferment for an extended period of time before being consumed. The risk is exacerbated when a plastic container is used for this purpose instead of the old-fashioned, traditional method, a grass-lined hole, as the botulinum bacteria thrive in the anaerobic conditions created by the air-tight enclosure in plastic.

The World Health Organization has classified pickled foods as a possible carcinogen, based on epidemiological studies. Other research found that fermented food contains a carcinogenic by-product, ethyl carbamate (urethane). ‘A 2009 review of the existing studies conducted across Asia concluded that regularly eating pickled vegetables roughly doubles a person’s risk for esophageal squamous cell carcinoma.’

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