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Author Topic: Fermentation Questions: Wine Making  (Read 5104 times)

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NurseIT

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Fermentation Questions: Wine Making
« on: January 29, 2007, 11:10:04 PM »

Hi there, kindly help me answer some questions regarding our wine making experiment using grape juice.

1) What's the chemical reaction involved in wine making?  Whats the chemical equation?

2) What's the purpose of the yeast and sugar? why are they added to the fruit juice?

3) What's the purpose of sterilization of the fruit juice? Why is the temperature not to exceed 122 degrees fahrenheit?
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P

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Re: Fermentation Questions: Wine Making
« Reply #1 on: January 29, 2007, 11:22:52 PM »

Hi there, kindly help me answer some questions regarding our wine making experiment using grape juice.

1) What's the chemical reaction involved in wine making?  Whats the chemical equation?

2) What's the purpose of the yeast and sugar? why are they added to the fruit juice?

3) What's the purpose of sterilization of the fruit juice? Why is the temperature not to exceed 122 degrees fahrenheit?

1 - fermentation of sugar to alcohol - look the equation up.
2 - Sugar goes to alcohol. Yeast speeds the fermentation by biologically breaking down the sugars. Fruitjuice contains more sugar and tastes nice.
3 - so as not to kill the yeast.
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Custos

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Re: Fermentation Questions: Wine Making
« Reply #2 on: February 08, 2007, 04:03:46 PM »

3) What's the purpose of sterilization of the fruit juice?

Fermentation conditions favour the growth of many micro-organisms, not just yeast. There are other fungi and bacteria present in the fruit juice. If it's not sterilised you could easily have one of these other unwanted organisms out-grow the years and cause all sorts of contamination problems.
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dazza95

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Re: Fermentation Questions: Wine Making
« Reply #3 on: March 19, 2012, 06:10:45 PM »

2 - Sugar goes to alcohol. Yeast speeds the fermentation by biologically breaking down the sugars. Fruitjuice contains more sugar and tastes nice.

So the more sugar you have, the more ethanol you make?,
the more yeast you have, the faster the fermentation process goes?
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billnotgatez

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Re: Fermentation Questions: Wine Making
« Reply #4 on: March 19, 2012, 06:20:04 PM »

Concentrations of sugar (input) and ethanol (output) influence ethanol production by yeast.

Quote
Yeast can't survive too high concentrations of sugars (osmotic pressure) and too high concentrations of ethanol (denaturation of proteins).

Links of interest
From this web site
http://www.yobrew.co.uk/home.php
you might look at
http://www.yobrew.co.uk/fermentation.php
http://www.yobrew.co.uk/wine.php


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dazza95

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Re: Fermentation Questions: Wine Making
« Reply #5 on: March 19, 2012, 07:42:55 PM »

Alright, Thanks for the links, We'll take a look :)
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Furanone

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Re: Fermentation Questions: Wine Making
« Reply #6 on: March 21, 2012, 03:11:34 AM »

2 - Sugar goes to alcohol. Yeast speeds the fermentation by biologically breaking down the sugars. Fruitjuice contains more sugar and tastes nice.

So the more sugar you have, the more ethanol you make?,
the more yeast you have, the faster the fermentation process goes?


The more sugar the higher alcohol up until a point where the alcohol is so high it starts killing the yeast. This is the self-regulating process, and different strains of yeast will have different tolerances to the ethanol content.

The more yeast you have, in general, the faster the fermentation will go, but other factors such as the temperature are also very important. Remember Arrhenius equation and that for every increase in about 10 degrees Celsius, the reaction rates double. The speed of the reaction is very important in generating the flavour of the wine. Fermenting too fast can generate off-flavours, while a slower fermentation at cooler temperatures tends to keep more aromatic compounds in the wine. This can be seen in the difference between red and white wines, where white wines are fermented at cool temperatures while reds at room temperature, and whites tend to have a lot more aroma notes such as esters, floral and citrus notes.
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billnotgatez

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Re: Fermentation Questions: Wine Making
« Reply #7 on: March 21, 2012, 05:42:23 AM »

@Furanone

Quote
The more yeast you have, in general, the faster the fermentation will go

The euphemism "Law of Diminishing Returns", I think might apply to the above statement.
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fledarmus

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Re: Fermentation Questions: Wine Making
« Reply #8 on: March 21, 2012, 06:27:16 AM »

2 - Sugar goes to alcohol. Yeast speeds the fermentation by biologically breaking down the sugars. Fruitjuice contains more sugar and tastes nice.

So the more sugar you have, the more ethanol you make?,
the more yeast you have, the faster the fermentation process goes?


 Remember Arrhenius equation and that for every increase in about 10 degrees Celsius, the reaction rates double.

The Arrhenius equation doesn't strictly apply to biological systems - living organisms are exquisitely sensitive to temperature, and the biological processes that they carry out are different with very small changes in temperature. In many cases, slight increases in temperature will cause the organisms to divert their metabolic resources to synthesizing heat-shock proteins and other protective mechanisms, and substantial increases in temperature will start killing off the weaker members of the population. It isn't so much the loss of aromatic compounds at room temperature that cause the different taste, but the yeast actually producing different compounds at different temperatures. And of course, the different breeds of yeast that are used for each different class of wine will give different flavors.
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Furanone

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Re: Fermentation Questions: Wine Making
« Reply #9 on: March 21, 2012, 07:23:28 AM »

2 - Sugar goes to alcohol. Yeast speeds the fermentation by biologically breaking down the sugars. Fruitjuice contains more sugar and tastes nice.

So the more sugar you have, the more ethanol you make?,
the more yeast you have, the faster the fermentation process goes?


 Remember Arrhenius equation and that for every increase in about 10 degrees Celsius, the reaction rates double.

The Arrhenius equation doesn't strictly apply to biological systems - living organisms are exquisitely sensitive to temperature, and the biological processes that they carry out are different with very small changes in temperature. In many cases, slight increases in temperature will cause the organisms to divert their metabolic resources to synthesizing heat-shock proteins and other protective mechanisms, and substantial increases in temperature will start killing off the weaker members of the population. It isn't so much the loss of aromatic compounds at room temperature that cause the different taste, but the yeast actually producing different compounds at different temperatures. And of course, the different breeds of yeast that are used for each different class of wine will give different flavors.

I agree that in terms of biological systems there are other contravening effects at work that disallow the Arrhenius equation, especially when enzymes are involved and different temperatures within this range can change metabolic pathways and at even higher temperatures these enzymes can become denatured completely halting the reaction. However, with this said, as someone who fermented six different whites and six different red wines at the same time (whites at 4 C, reds at 21 C) while monitoring the alcohol production twice daily, I can safely say the red finished in half the time as the white wines to reach similar alcohol content (~12-14.5%). In subsequently analyzing the flavour compounds by GC-MS, i can also say the whites qualitatively had about double the variety of compounds (peaks) and quantitatively over three times the total amount of flavour compounds.

And when you say "It isn't so much the loss of aromatic compounds at room temperature that cause the different taste, but the yeast actually producing different compounds at different temperatures", I must say it is both. The flavours (aroma volatiles) are the yeast metabolites from the produced enzymes that hydrolyze glycosides (sugars attached to flavour compounds) as well as larger proteins and other polymers that release the flavours. The more hydrophobic ethanol produced helps hold the hydrophobic volatiles in solution better than water, but flavours are still lost over the fermentation time. A quick smell of the air lock of the reds at room temp shows a much stronger aroma than that of the refrigerated whites, as those aroma compounds tend to remain more in the wine. But I agree the conditions of the yeast are very important, and can greatly affect what enzymes are produced and what glycosides are hydrolyzed to release very different flavour compounds. And just to complicate things further one of the whites was done at 21 C and one red refrigerated at 4 C, and the temperature of fermentation was a very powerful variable making the red retain the highest of all red flavour compounds, while the white had the lowest total aroma compounds (based on GC-MS analysis).
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"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

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