# What makes a grape ferment?

**URL:** <https://boards.straightdope.com/t/what-makes-a-grape-ferment/210112>\
**Category:** Factual Questions\
**Created:** [October 28, 2003, 10:22pm UTC](https://boards.straightdope.com/t/what-makes-a-grape-ferment/210112 "2003-10-28T22:22:54Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![moejuck](https://avatars.discourse-cdn.com/v4/letter/m/57b2e6/32.png) [@moejuck](https://boards.straightdope.com/u/moejuck)\
**Post date:** [October 28, 2003, 10:22pm UTC](https://boards.straightdope.com/t/what-makes-a-grape-ferment/210112/1 "2003-10-28T22:22:54Z")

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I know why it ferments, but was wondering if there was a specific chemical that caused this reaction to occur.

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**Author:** ![pravnik](https://avatars.discourse-cdn.com/v4/letter/p/8edcca/32.png) [@pravnik](https://boards.straightdope.com/u/pravnik)\
**Post date:** [October 28, 2003, 10:30pm UTC](https://boards.straightdope.com/t/what-makes-a-grape-ferment/210112/2 "2003-10-28T22:30:49Z")

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Nothing fancy; the yeasts on the skin comes in contact with the grape sugars, which gets converted into ethyl alcohol and carbon dioxide. Sometimes cultured yeast is added by winemakers to help the process along.

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**Author:** ![moejuck](https://avatars.discourse-cdn.com/v4/letter/m/57b2e6/32.png) [@moejuck](https://boards.straightdope.com/u/moejuck)\
**Post date:** [October 28, 2003, 10:40pm UTC](https://boards.straightdope.com/t/what-makes-a-grape-ferment/210112/3 "2003-10-28T22:40:53Z")

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Can you write out the chemical reaction by any chance?

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [October 29, 2003, 12:26am UTC](https://boards.straightdope.com/t/what-makes-a-grape-ferment/210112/4 "2003-10-29T00:26:16Z")

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Glucose -\> Glucose 6-phosphate -\> Fructose 6-phosphate -\> Fructose 1,6-diphosphate -\> Glyceraldehyde 3-phosphate (2 molecules) -\> 3-Phosphoglyceroyl phosphate (2) -\> 3-Phosphoglycerate (2) -\> 2-Phosphoglycerate (2) -\> Phosphoenolpyruvate (2) -\> Pyruvate (2) -\> Acetaldehyde (2) -\> Ethanol (2).  
Here’s the first part of the pathway [through Pyruvate](http://www.icr.org/pubs/imp/imp-090.htm), and here’s the conversion of Pyruvate to acetaldehyde, then [Ethanol](http://campus.northpark.edu/biology/cell/anaerobicresp.html).

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**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\
**Post date:** [October 29, 2003, 3:05am UTC](https://boards.straightdope.com/t/what-makes-a-grape-ferment/210112/5 "2003-10-29T03:05:24Z")

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Another way to put it is the way writer Kurt Vonnegut did in his novel _Breakfast of Champions_. The yeast injests the sugar and excretes alcohol. Vonnegut described a scene in a bar as people “sitting around drinking yeast excrement.”

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [October 29, 2003, 3:29am UTC](https://boards.straightdope.com/t/what-makes-a-grape-ferment/210112/6 "2003-10-29T03:29:20Z")

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That’s _much_ more romantic sounding 😛