Why does anyone use a hydrometer?

[scheelings]

When the chemistry is more accurate? (assuming all sugar is fermented)

For those that like Chemistry:

C12H22O11 + H2O + invertase => 2 C6H12O6

C6H12O6 + Zymase => 2 C2H5OH + 2 CO2

So 1 mol of sucrose yields 4 mols of ethanol.

Molar mass of sucrose = 342.30 g/mol (based on molecular weight)
Molar mass of ethanol = 46.06844 g/mol

Therefore 342.3g of sucrose, yields 184.273 g of ethanol

Or more conveniently, every 100g of sugar, yields 53.8g of ethanol

The density of ethanol is 0.789 g/cm³
1L ethanol = 0.789*1 => 0.789KG

Therefore 53.8g of ethanol = 68.23 millilitres of ethanol

This volume can be assumed to be produced for every 100g of sugar added as long as the alcohol threshold remains below the theoretical upper limit of the yeast.

For those that don't:

So every 1kg of sugar added to a 30 litre brew, increase the alcoholic content by 2.22%.

 

[iceo]

well i use mine to tell me its safe to bottle my brews(dont want bottle bombs)

 

[MacKiwi]

There are plenty of variables that your equations don't accommodate...

Not all sugar from grain is sucrose.
Not all sugar is fermented.
Mash efficiency isn't consistent

Still, I love a bit of science. :thumb: But if it was that simple, there wouldn't be much magic in brewing :)

 

[bunkerbrewer]

When the chemistry is more accurate? (assuming all sugar is fermented)

How do you know how much "sugar" you're starting with before fermentation begins...? :)

 

[Duxuk]

I use a hydrometer because I like to be able to say.........."It's 1053 you know. Hope you're not driving"
I have a degree in chemistry but brewing and cooking are the only chemistry I do now.

I've been using an equation in my AG to calculate efficiency. I don't know if it's accurate but it compares the mash efficiency of brews and needs a hydrometer.

%efficiency = (OG-1000)*100/(Kg grain*295/brew length)

Yesterday I did (1046-1000)*100/(4*295/23)=89.661%

This is a figure I was well pleased with. See my BITS brewing thread in "How to " guides. It's AG made simple and cheap. Someone described it as ghetto brewing. I like that :thumb:

Andrew BSc(hons) Chemistry. Haven't written that in living memory!

 

[pittsy]

yep a scientist invented a hydrometer and then an engineer made one and then I bought it so i'll stick to using a tool invented to make life easier and fairly accurate too , don't you .

 

[rpt]

(assuming all sugar is fermented)

A theory is useless when the axiom is wrong.

 

[graysalchemy]

You , make one big assumption.............

All the sugar is fermented.

If you brew all grain you don't have an accurate figure of what sugar you have and since there are so many variables which will affect how much fermentable and non fermentables are produced in the mash it is nigh impossible without sending you wort to a lab to be analysed.

Secondly you are assuming that you yeast will ferment all the sugar, that is not necessarily the case and you may get a stuck ferment in which case you may think it is done but in fact it isn't.

So i prefer sticking a little glass stick in every now and then taking the OG and the final gravity and then using the little calculator in the menu top left.

Brewing is a science it is an alchemy with more variables than you would find in your average undergraduates chemistry experiment.

If you want to impress us with your chemistry prowess, then please take time to look at the subject that you are trying to apply it to, a subject that we know very well and you obviously have little knowledge of.

 

[fbsf]

It's not just chemistry. It's biology too.

And a £4 glass stick seems remarkably accurate in telling me how the biology has affected the chemistry...

 

[Aleman]

When the chemistry is more accurate? (assuming all sugar is fermented)

And that is a BIG assumption,

Not all the sugar is glucose/sucrose/maltose etc, there are other 'sugars' present that are not fermentable, but these still contribute to the gravity reading.

SG - OG tells you what has fermented . . . Rather than just assuming that 100% will ferment :whistle:

Of course the Cheaper Glass Sticks, and poor methodology makes it about as accurate as a Chimpanzee with a blunt stick!

 

[alanywiseman.]

I use it to see how brews are progressing. Generally I don't care that much about the final ABV, ball park figures are fine for me.

I also second what others have said above, preventing bottle bombs, too many variables not considered etc

 

[Hawks]

Of course the Cheaper Glass Sticks, and poor methodology makes it about as accurate as a Chimpanzee with a blunt stick!

:rofl:

 

[scheelings]

Thank you all very much for your replies. I didn't realize that not all sugars ferment.

When using a hydrometer, as the ethanol content increases, the density of the brew becomes lower - Can you tell the alcohol content from the final reading only? Or do you need 2 readings since possibly depending on what you are brewing - that the original brew is likely to be denser than water.

 

[Hawks]

You need a reading at the start and another at the end - you can then use the calculator in the links section :thumb:

 

[anthonyUK]

Can you tell the alcohol content from the final reading only?

For someone with an ounce of science knowledge that is a very stupid question with relation to brewing.
Unless you know exactly the composition of your liquid it would be impossible to work out its alcohol content by weight alone.
As mentioned there are very many compounds in play at any one time all with varying weights etc and these can react with one another over time.
Hence why we use a hydrometer.

K.I.S.S. works for me.

 

[adrianmole72]

AND it makes us look a bit like scientists !

 

[rpt]

For someone with an ounce of science knowledge that is a very stupid question with relation to brewing.

Don't hold back. Tell him what you really think.

 

[IPA]

If you want to impress us with your chemistry prowess, then please take time to look at the subject that you are trying to apply it to, a subject that we know very well and you obviously have little knowledge of.

These are words of widom and experience please take heed!

 

[Baz Chaz]

When the chemistry is more accurate? (assuming all sugar is fermented)

It all went pear shaped for me as soon as on word was put into the above statement .... assuming :nah:

Don't take it to heart scheelings, just read your own statements before posting, we all drop the odd clanger now and again

 

[Jimmy321]

When the chemistry is more accurate? (assuming all sugar is fermented)

For those that like Chemistry:

C12H22O11 + H2O + invertase => 2 C6H12O6

C6H12O6 + Zymase => 2 C2H5OH + 2 CO2

So 1 mol of sucrose yields 4 mols of ethanol.

Molar mass of sucrose = 342.30 g/mol (based on molecular weight)
Molar mass of ethanol = 46.06844 g/mol

Therefore 342.3g of sucrose, yields 184.273 g of ethanol

Or more conveniently, every 100g of sugar, yields 53.8g of ethanol

The density of ethanol is 0.789 g/cm³
1L ethanol = 0.789*1 => 0.789KG

Therefore 53.8g of ethanol = 68.23 millilitres of ethanol

This volume can be assumed to be produced for every 100g of sugar added as long as the alcohol threshold remains below the theoretical upper limit of the yeast.

For those that don't:

So every 1kg of sugar added to a 30 litre brew, increase the alcoholic content by 2.22%.

TL;DR

This is why you should use a hydrometer