This news item was created by students Mike Borgstadt, Todd Bennett, Howard Wang and Greg Watson as part of their Chemistry 210 Semester Project in WS99 under the guidance of Prof. Rainer Glaser.

Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 11. Reactions of Alcohols.


For each of the following questions, please refer to the following article:
SECONDARY FERMENTATION
by Ray Daniels, Homebrewing, 1996.


Editorial Comments

Pertinent Text References
Chapter 10: Structure and Synthesis of Alcohols
Chapter 11: Reactions of Alcohols.

Before Anheuser-Busch and other breweries were established, home-brewing was the only way to make the beverage of champions, BEER. Home-brewing has been going on since 1800 BC and people continue to brew their own beer in their homes today. People of all ages drink beer, although very few know the processes that govern its road to reality.

Brewing your own beer is actually an easy process consisting of two steps: primary and secondary fermentation. In these processes sugar, carbon dioxide, and alcohol (i.e. ethanol) are involved.

Primary fermentation consists of the conversion of sugar, which is obtained from grains such as corn, wheat, rye, and barley, to ethanol and carbon dioxide. Carbon dioxide is released violently in this chemical reaction which is propelled by yeast.

In secondary fermentation, yeast takes over and expunges the undesirable chemicals, which in turn makes the beer more drinkable. Towards the end of secondary fermentation, the yeast ends up settling at the bottom of the container and is filtered off.

Fermentation of sugar into ethanol is a relatively inexpensive process, but with the numerous taxes on alcohol, makes the purchasing of it rather expensive.

Consumption of ethanol also has side effects. One of these is an intoxicating result. This is the reason why many people drink the beverage. It impairs one's vision, reactions, and ability to make judgements because of the massive killing of brain cells. Many groups because of these side effects, such as MADD, have promoted mature management of alcohol.

Many people brew their own beer because it allows them to control the taste of the beverage to their own personal preferences.



Questions

Question 1: Write the balanced chemical equation for the synthesis of ethanol from glucose.


A. 1 glucose ===> 2 carbon dioxide + 2 ethanol. With yeast as a catalyst.


Question 2: 2. How long does primary fermentation take to occur and what happens in this process?


A. Primary fermentation takes approximately three to five days and is known for its violent release of carbon dioxide (CO2) during the reaction along with the production of ethanol (C2H6O).


Question 3: What are some of the unwanted side products that are produce during the fermentation of alcohol? Why are the chemicals not wanted in the beer?


A. Diacetyl, acetylaldehyde, and some sulphur compounds. These chemicals make the beer harder to drink because of their undesirable tastes.


Question 4: What marks the close of primary fermentation?


A. As primary fermentation draws to a close, less CO2 is forming which causes a decrease in the number of bubbles forming.


Question 5: Draw the structure of ethanol and describe its properties. (Hint: see chemfinder.)


A. Ethanol is a flammable liquid at room temperature and is very volatile. It has a low melting point and is a colorless.


Question 6: Why does the beer appear darker at the top than the bottom?

A. As the reaction draws to a close, the yeast settles to the bottom therefore there are less yeast particles at the top to reflect light.