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Author Topic: How do they take the caffeine out of coffee to make "decaff"?  (Read 7679 times)

paul.fr

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How is coffee decaffeinated?
« Last Edit: 29/05/2010 10:27:03 by chris »


 

Offline dentstudent

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The question should be "WHY"!  [V]

What's the point of coffee without the caffeine?
 

Online Bored chemist

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They wash the coffe with solvent. They used to use dichloromethane (better known as paint stripper) I think they now use liquid CO2.
The tricky bit is then returning some of the other stuff that gets extracted in order to preserve the flavour.
As for why, that's easy. Where else would you get the caffeine that goes into those little pills?

 

Offline Carolyn

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They wash the coffe with solvent. They used to use dichloromethane (better known as paint stripper) I think they now use liquid CO2.
The tricky bit is then returning some of the other stuff that gets extracted in order to preserve the flavour.
As for why, that's easy. Where else would you get the caffeine that goes into those little pills?



Does that make caffeinated coffee less harmful than decaffeinated?
 

Offline eric l

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Does that make caffeinated coffee less harmful than decaffeinated?

I hope you are not intending to add extra caffeine to your coffee.
Anyway, it will depend on the person :  if you are subject to high blood pressure, to insomnia or to two or three other things, caffeine is more harmful to you than these solvent(s) would be. 
AFIK dichloromethane is no longer used for decaffeinating, and I take it that any solvent that is used nowadays is considered "safe", which does not mean that they may not be considered "suspect" or "harmful" somewhere in the future.
 

Offline Carolyn

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Does that make caffeinated coffee less harmful than decaffeinated?

I hope you are not intending to add extra caffeine to your coffee.Anyway, it will depend on the person :  if you are subject to high blood pressure, to insomnia or to two or three other things, caffeine is more harmful to you than these solvent(s) would be. 
AFIK dichloromethane is no longer used for decaffeinating, and I take it that any solvent that is used nowadays is considered "safe", which does not mean that they may not be considered "suspect" or "harmful" somewhere in the future.

Thank you for correcting my redundancy and for the answer. :)
 

Offline Cut Chemist

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Its strange that a nonpolar solvent (dichloromethane) will strip caffeine out of coffee as efficiently as hot water.  Why is this the case??

I realize that caffeine is an uncharged relatively polar compound (because of the nitrogen atoms and the carbonyls,) but most of the time for a compound to be soluble in water it must be a charged species.  It seems like an acid/base extraction would be necessary.

However, every morning I'm proved wrong, when I brew a cup of coffee with hot water.
« Last Edit: 18/08/2007 02:16:20 by Cut Chemist »
 

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Caffeine isn't very soluble in water (1 gram in 46 ml) compared to chloroform (1 gram in just 5.5 ml). (sorry, I can't find the data for DCM but chloroform is close). Incidentally, DCM is actually quite a polar solvent.
However since a cup of coffee only needs something like 0.1g of caffeine to dissolve and uses something like 200 ml of hot water, there's no problem dissolving all the caffeine. I know that caffeine sublimes quite easily so I guess the molecules are not very strongly held together in the crystal. Presumably the interactions with the polar C-Cl bonds are sufficient to overcome the bonds holding the crystal together.
I suspect that the low water solubility might be as much to do with the unfavourable disruption of hydrogen bonds between water molecules as with a lack of favourable dipole interactions between caffeine and water.
An acid / base type extraction isn't very good for caffeine because it's not a very strong base (or acid come to that). In order to protonate or deprotonate it you would need quite aggressive acids or bases which would ruin the flavour of the coffee.
 

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