What is alcoholic fermintation?

Answer 1

- fermentation of sugars is process which occur under anaerobic conditions (absent of oxygen) by micro organisms which convert the sugars into products depend on kind of micro organisms.

- the types of fermentation of glucose is:
(homolactic acid, alcoholic, mixed acids, butylenes glycol, propionic acid, butyric-butyric).

- in glycolysis glucose convert to 2 molecules of pyruvate which is convert to 2 molecules of lactate (homolactic acid fermentation) and convert to 2 molecules of ethanol (alcoholic fermentation).

- homolactic acid fermentation
The overall reaction:
C6H12O6 + 2NAD+ +2ADP + 2Pi >>>> 2C3H6O3 + 2NAD+ + 2ATP.
(C3H6O3 is lactice acid)

- alcoholic fermentation
The overall reaction:
C6H12O6 + 2Pi + 2ATP + 2ADP >>>> 2C2H5OH + 2CO2 + 4ATP .
(C2H5OH is ethanol)

- homolactic acid fermentation & alcoholic fermentation all of them occur by bacteria and use yeast as source of enzymes.

Answer 2

Process by which yeast finishes the break-down of glucose into ethyl alcohol and carbon dioxide in the absence of oxygen, having a net gain of only 2 ATP per glucose.

Answer 3

In brewing, alcoholic fermentation is the conversion of sugar into carbon dioxide gas (CO2) and ethyl alcohol. This process is carried out by yeeast enzymes. This is in fact a complex series of conversions that bring about the conversion of sugar to CO2 and alcohol. Yeast is a member of the plant family and in brewing we use the sugar fungi form of yeast. These cell gain energy from the break down of the sugar. The by-product, CO2, bubbles through the liquid and dissipates into the air. The other by-product alcohol, remains in the liquid which is great for us but not for the yeast, as the yeast dies when the alcohol exceeds its tolerance level.
Brewer's yeast tolerate up to about 5% alcohol. Beyond this alcohol level the yeast cannot continue fermentation. Wine yeast on the other hand tolerates up to about 12% alcohol. The level of alcohol tolerance by yeast varies from 5% to about 21% depending on yeast strain.
The fermentation process has other limits such as temperature. Greater than 27C kills the yeast less and than 15C results in yeast activity which is too slow.
The amount of sugar in the solution can be too much and this can prevent fermentation. Some recipes suggest adding the sugar in parts throughout fermentation rather that all at the beginning. This is especially true if the brew is aimed at producing a high level of alcohol. Some yeast strains have evolved to handle higher sugar levels. Yeast such as Tokay and Sauterne.

The normal, home brewing, fermentation is in two parts.
Part 1
Aerobic (Oxygen is present)
This is the initial rapid process where the yeast is doubling its colony size every 4 hours.
(Usually 24-48 hours)

Part 2
Anaerobic. (No oxygen present)
Slower activity and the yeast focuses on converting sugar to alcohol rather that increasing the number of yeast cells.
(This process can take from days to weeks depending on the yeast and the recipe)




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Overall chemistry of fermentation


The overall process of fermentation is to convert glucose sugar (C6H12O6) to alcohol (CH3CH2OH) and carbon dioxide gas (CO2). The reactions within the yeast to make this happen are very complex but the overall process is as follows:
C6H12O6 ====> 2(CH3CH2OH) + 2(CO2)
Sugar ====> Alcohol + Carbon dioxide gas
(Glucose) (Ethyl alcohol)


Note: The sugars used can be a range of fermentable sugars. These sugars are converted by enzymes to glucose which is then convered to alcohol and CO2
Alcohol Fermentation
Alcohol fermentation is done by yeast and some kinds of bacteria. These microorganisms convert sugars in ethyl alcohol and carbon dioxide. Alcoholic fermentation begins after glucose enters the cell. The glucose is broken down into pyruvic acid. This pyruvic acid is then converted to CO2, ethanol, and energy for the cell. Humans have long taken advantage of this process in making bread, beer, and wine. In these three product the same microorganism is used: the common yeast or Saccharomyces Cerevisae.


Bread fermentation
During the fermentation process of bread, sugar is converted into alcohol and carbon dioxide. The carbon dioxide will form bubbles, which will be trapped by the gluten of the wheat causing the bread to rise. Because the bread fermentation takes a short period only small amounts of alcohol are formed, most of which will be evaporated during the bread baking process. Therefore, you want get drunk by eating bread!
Wine fermentation
Saccharomyces is responsible for the alcohol fermentation of wines. Grape juice contains naturally high levels of sugars. These sugars are converted into alcohol and carbon dioxide. Natural fermentation can yield wines with an alcohol up to 16 percent.
Alcohol fermentation is an anaerobic (no oxygen), exothermic (heat-releasing) process in which sugars break down into ethyl alcohol CH3CH2OH and carbon dioxide gas, catalysed by microbial or fungal enzymes.


When yeast is grown under anaerobic conditions, sugars are fermented to alcohol and carbon dioxide. At about a concentration of 12%, ethanol itself inhibits further growth of the microbial organisms and the process stops.





The process follows the formula:


C6H12O6 --> 2 C2H5OH + 2 CO2 + 23 Kcal


It consists of a number of complex chemical reactions during which glucose is gradually oxidized into pyruvic acid then converted to ethanol.






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Although the phenomenon of fermentation was known and used in ancient times (leavening bread, brewing, vintaging, vinegar-making),
its component processes were not revealed until much later:


Georg E. Stahl formulated the theory of fermentation in 1697.
He put forward the concept of enzymes, catalyzers of reactions.

Antoine-Laurent Lavoisier described the chemistry of fermentation in 1787, and Nicolas Theodore de Saussure quantified its constituent relations in 1814.

In 1897, the brothers Eduard and Hans Buchner extracted "zymase", the set of enzymes which catalyse alcohol fermentation from homogenized yeast extracts.



An anaerobic step that yeast use after glycolysis that breaks down pyruvic acid to ethanol and carbon dioxide.