End of Fermentation 0.998. Why?

[xdfireguy]

Maybe I missed this, and admittedly I am new to the higher OG arts, but I understand that fermentation is complete at or slightly below 0.998. What I am curious about is why?

Is it a factor of the OG and yeast just giving up once the alcohol level increases beyond their tolerance levels? For example, if you start with a lower gravity level would the ending gravity level also drop? It seems like 0.998-0.995 is the magic number to end all wines.

Of course, it is probably something simple that I can't pull out of my foggy brain right now - and google isn't helping me!

 

[janivar123]

Well no
Alcohol is lighter then water so as long as the yeast dont get exhausted higher OG should give a lower FG

 

[Dicky]

Basically, there's no more sugar left in the liquid.

Sugar makes the water heavier giving it a higher static gravity, as the yeast eats the sugar and produces alcohol the SG drops. The SG of pure water is 1.000, Thus, when the SG drops below that the fermentation is done.

Which is why you ferment to "dry'.

Dicky

 

[Yooper]

Most "normal" wines with an OG of 1.100 or so will ferment to .990. That's because alcohol "weighs" less than water and water is 1.000. Once there are no more fermentable sugars, if the yeast isn't overwhelmed by alcohol, a typical wine/mead/cider will end up at .990 or so.

 

[xdfireguy]

Thank you Dicky & Yooper. Water=1.000 thus no more fermentables is the missing link my mind couldn't put together somehow.... why I couldn't put together the basics is beyond me.

 

[DoctorCAD]

Thank you Dicky & Yooper. Water=1.000 thus no more fermentables is the missing link my mind couldn't put together somehow.... why I couldn't put together the basics is beyond me.

Too much wine????

 

[Dicky]

Too much wine????

No such thing.

Dicky

 

[ashfatboy]

Ok
Maybe I am being stupid here.
If at .9 I add **** loads or sugar the wine will not ferment more because the yeast can't tolerate more alcohol % and that's sweetening the wine???
(and I am drunk)

 

[xdfireguy]

I am a little more clear-headed right now so let me give this a shot.

If: a) The yeast have been "killed off" and you have racked off of the bulk of the sediment, or
b) The alcohol level is in excess of what the yeast will survive in

you might not restart fermentation.

I just added a boat load of fermentables to a cranberry lemonade after knocking down the Cotes de Blanc with Campden and K-Sorbate. 1 week later no signs of refermentation.

 

[WhtHawk]

xdfireguy,

It looks like you have the basic idea. Yeast will stop fermenting when: 1) There are no additional fermentables; 2) The yeast are dead.

There are several ways to end up with dead yeast: 2A) Enough alcohol has been produced or added so that it is toxic; 2B) The addition of stabilizers have prevented the yeast from re-producing and the yeast have simply lived their lives and died of old age; 2C) The beverage is pasteurized with heat; 2D) Another anti-microbial treatment is applied such as UV light; 2E) Option 1 plus time, aka there is no food left and the yeast eventually die of starvation.

Of course there is option 3, you can use a "sterile" filter to remove the yeast.


What this means is that fermentation is done when the Specific Gravity stops changing over the course of at least two weeks. It does not mean that it is any particular value of specific gravity as it is possible to provide more fermentables than the yeast can convert to alcohol. Since sugar is more dense than water which is more dense than alcohol, the SG can be greater-than one, equal-to one, or less-than one.

 

[Banjoe]

This is the most informative string of information I've read in a long time and I've picked up quite a bit of insight into the little yeast creatures.

Thanks for sharing your knowledge folks.

 

[stujol]

What is the life span of yeast ? If I add potassium sorbate and campdens, how long would it take the remaining yeast to die from old age ? And does that life span change if there is still fermentables present ?

xdfireguy,

It looks like you have the basic idea. Yeast will stop fermenting when: 1) There are no additional fermentables; 2) The yeast are dead.

There are several ways to end up with dead yeast: 2A) Enough alcohol has been produced or added so that it is toxic; 2B) The addition of stabilizers have prevented the yeast from re-producing and the yeast have simply lived their lives and died of old age; 2C) The beverage is pasteurized with heat; 2D) Another anti-microbial treatment is applied such as UV light; 2E) Option 1 plus time, aka there is no food left and the yeast eventually die of starvation.

Of course there is option 3, you can use a "sterile" filter to remove the yeast.


What this means is that fermentation is done when the Specific Gravity stops changing over the course of at least two weeks. It does not mean that it is any particular value of specific gravity as it is possible to provide more fermentables than the yeast can convert to alcohol. Since sugar is more dense than water which is more dense than alcohol, the SG can be greater-than one, equal-to one, or less-than one.

 

[Yooper]

What is the life span of yeast ? If I add potassium sorbate and campdens, how long would it take the remaining yeast to die from old age ? And does that life span change if there is still fermentables present ?

Yeast will life indefinitely but go dormant. The sorbate inhibits yeast reproduction, so new yeast can't be made but the yeast already in the wine won't die.