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Name: Lily
Status: student
Grade: 9-12
Location: N/A
Country: N/A
Date: 1/5/2006
Question:
In beer brewing, I know that the basic reactions are: starch --> fermentable sugars & sugar --> alcohol + carbon dioxide. The balanced chemical equation of sugar to alcohol is C6H12O6 --> 2(CH3CH2OH) + 2(CO2), however I need to know the equation of starch to sugar.

Replies:
Starch is a large molecule that is made of branching chains of glucose molecules. It doesn't really have a simple chemical formula, like the ones you list in your question. Cells can break starch down into glucose by taking the chains apart. This kind of reaction, called hydrolysis, requires water as one of the reactants. I recommend looking at any introductory biology textbook for diagrams that show how glucose molecules can be put together and taken apart. The web sites below also show molecular diagrams of starch molecules. Unfortunately, you won't find a simple chemical equation for the reaction. The starch molecules involved are too big and complex for simple formulas.

http://www.pslc.ws/mactest/starch.htm

http://www.poco.phy.cam.ac.uk/research/starch/whatis.htm

C. Perkins

Hi Lily!

natural starch is a polymer of glucose and can be separated into 2 fractions:one, called amylose forms a colloidal dispersion in hot water.The other, amylopectin is completely insoluble. Both forms are composed only of D-glucose units. Amylose consists of un unbranched chain of glucose units joined from the first to the fourth carbons by alpha linkages. There may be from 60 to 300 glucose units per chain.

Amylo pectin has similar chains, and it also has branches off the sixth carbon. There may be 300 to 6000 glucose units per amylo pectin molecule. Commercial starch is a white powder that under controlled conditions can be partially hydrolized. Hydrolisis is catalyzed by acids and by enzimes and leads ultimately to the formation of glucose. So as you can see the chemical equation, of that transformation even the over all is too much complicated to be represented here in that site.

Thanks for asking NEWTON!

Mabel (Dr. Mabel Rodrigues)


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