Kendra Parr
University of New Hampshire, Manchester



Wine-making is done in a variety of different ways however each process is reliant on the same anaerobic condition, ethanol fermentation. Ethanol fermentation is the process of converting sugars into ethanol and carbon dioxide (by product) that is preformed by yeast and a few types of bacteria. Because this process produces carbon dioxide as a by product, the emission of carbon dioxide increases within the environment causing an increase in the greenhouse effect within the earth's atmosphere. This experiment was demonstrated to capture the carbon dioxide released from the fermentation process to make wine and to use the captured CO2 for significant purposes thus creating a "greener" process to potentially decrease the amount of CO2 given off in the production of wine making.

The Biochemistry of Wine Production:

Before jumping into the experiment we must know what is happening exactly in this procedure and what materials are used and how. In cellular respiration, sugar goes through glycolysis and is converted into pyruvate as an end product. If oxygen is not present, the pyruvate has an option of going through ethanol fermentation. This process takes place in two steps:

1.) Pyruvate decarboxylase converts pyruvate into acetaldehyde and releases CO2
2.) Alcohol dehydrogenase now converts acetaldehyde into ethanol

Ethanol Biochemical Pathway (Permission: Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.)
Ethanol Biochemical Pathway (Permission: Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.)
It is estimated that one mole of glucose yields two moles of ethanol and two moles of carbon dioxide. This process takes place within the activated yeast cells. The most commonly cultured yeast used is Saccharoyces cerivisiae because it can also metabolize under aerobic conditions. In order for yeast to produce ethanol it must have a continuous supply of carbon, nitrogen, sulfur, phosphorous and other nutrients that are supplied by the fruit or fruit juices.
Now the Actual Procedure:The purpose of this experiment is to try and capture the CO2 released to not only reduce the emission but also attempt to use it for additional products. Therefore, the set of the experiment requires the use of a balloon to be attached tightly around the caped space of the glass bottle were it the CO2 would be trying to escape so that as much gas can be collected as possible (or rather as much CO2 gas as the balloon can expand to hold). It's also important to seal this area off tightly so that no O2 can enter and disrupt the process.
(Photo taken by Kendra Parr) Sugar, 100% Juice Concentrate, Two 1-Gallon Glass Jars, Yeast, and a Balloon

As you can see all these items are basic household items. It is important to try and use glass containers over plastic because the alcohol being produced may evaporate through the plastic or may be corroded by the chemical reaction (and, let's face it, also because this is a "Green" chemistry experiment). First step was to pour the juice concentrate into one of the glass jugs along with some water then 16 grams of sugar was added into the mix, although, not too much water was added in because the higher concentration of sugar is needed to feed the yeast as well give the wine a sweet flavor over a yeast flavor(?). The yeast must be activated before combined with the mixture which was basically done by adding it to some hot water (make sure the water is not too hot so you do not kill them, about 90 degrees F).

(Photo taken by Kendra Parr) Addition of the Yeast

The mixture was shaken up well so that the sugar did not just accumulate at the bottom. Finally the Balloon was attached to the top inverted in the glass jar and was placed in an area that is dark because UV light from the sun will damage it by causing the degradation of otherwise stable organic compounds found in it.

(Photo taken by Kendra Parr)

(Photo taken by Kendra Parr) Two days after fermentation

After two days of fermentation the balloon has inflated with CO2 gas outside of the jar. CO2 is 15 times heavier than air which explains why the balloon is not holding up so well.

During the Fermentation Process:
The yeast enzymes turn glucose and fructose into ethanol and carbon dioxide. This continues until the alcohol reaches about 14% (or 18% if it's a wine yeast), and then the alcohol kills the yeast. All of the CO2 is being collected within the balloon, therefore if the balloon is expanding too much to were it may burst you can take it off, cap the jar, and place it in the refrigerator. The refrigeration temperature is cold enough for the yeast to become dormant (alive but not active) thus creating no more CO2. If the balloon appears to be holding up well then allow the wine to ferment for about 3 weeks, however, in this case we will only let it go for about 2 so that the built up pressure of CO2 does not cause the balloon to explode and defeat the purpose of the experiment. Once the time is up, take the balloon off and tie it so that hopefully no gas can escape. The purpose of the other glass jar is to siphon the contents of the first into it therefore leaving out any unnecessary sediments. Cap the jar and allow it to be refrigerated for about another 2-3 weeks this way the acids in the wine will gradually react with some of the alcohol to form esters, which change the flavor of the wine from tangy to fruity.

Wineries obviously release a tremendous amount of CO2 into the environment and there is little to be done to prevent this from occurring. However, the capture of CO2 can be used for additional purposes such as carbonation for sparkling wines as well as beer and soda. This method of carbonating a beverage is called natural carbonation or bottle conditioning. While making soda, yeast is added to the solution for carbonation. The yeast eats some of the sugars in the soda which gives off CO2 and a small amount of alcohol (not a significant amount of alcohol). The trapped CO2 builds up enough pressure and carbonates the soda. Same process with beer and wine. Although the recapturing of CO2 is difficult and costly it would still be a benefit to the environment.