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Yeast and fruit: how to gain high ethanol production

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Yeast and fruit: how to gain high ethanol production
Naaborg, Zhang, Rashaan
Christelijk Lyceum Delft, The Netherlands
Summary
The production of bio-ethanol from sugars is a widely known method to gain specific bio fuel. This process is especially beneficial because in the future oil resources will be scarce. Fruit and vegetable markets produce a large amount of waste each year and its disposal costs a lot, both financially and environmentally. It has been proven that this waste can be upgraded to products of higher value so we wanted to see which fruit develops the optimum ethanol production.
We decided to go for three kinds of fruits: apple, banana and grapes. We want to gain ethanol in the end so we decided to go for yeast addition. The process that now Introduction
Yeasts are simple single celled micro organisms that can convert sugar, by reacting it with oxygen, to carbon dioxide and water. In the absence of oxygen, yeasts can convert sugars to alcohol and carbon dioxide, and continue living until they make so much alcohol they die (about 12 to 13%). By adding yeast Saccharomyces cerevisiae, the fermentation can start with help from the sugars from the fruits.
Approach To begin with, the banana, apple and grapes are smashed into a small bowl, all separately.
We eliminate hard parts, such as the small seeds from the grapes and the apple core.
We dissolve 20 grams of each fruit in 150 mL of water. The solution now consists of 170 mL of liquid so we have a fruit concentration of 11.8 %. (Per fruit solution this is)
The fruit concentration is then poured into a flask. In this flask we add some baker's yeast so that the fermentation can start. We lock the flask with a rubber stop. Trough the rubber stop a little tube runs from the flask to a bigger water-filled flask.
To prevent the escape of gasses, we put a graduated cylinder filled with water, into the bigger flask so that the small tube is covered with the cylinder. This has to be done in an accurate way so that there is no chance of getting bubbles into the bigger flask. So the graduated cylinder is covered first with a piece of paper and then put in the flask. We now can remove the piece of paper. The gases that now try to escape, coming from the flask wich is filled with the fruit and yeast, are captured due to the graduated cylinder. Secondly, we put the three different arrangements in thermo baths of 35 degrees Celcius. After 2 hours we look again so we can conclude how much gas developed in the graduated cylinder.
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