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Author Topic: Why does beer froth up when poured into a glass?  (Read 5229 times)

Dave Tootill

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Why does beer froth up when poured into a glass?
« on: 11/07/2009 12:30:01 »
Dave Tootill  asked the Naked Scientists:
   
You can pour bottled real beer into a glass very easily.
 
If you pour a down-market beer made with CO2, you have to be very careful to pour it sideways so as not to waste some of it onto the Formica bar top.  
 
Please describe the chemical reaction.
 
Dave

What do you think?


 

Offline Chemistry4me

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Why does beer froth up when poured into a glass?
« Reply #1 on: 14/07/2009 02:21:12 »
Please describe the chemical reaction.
A pressurised dilute solution of carbonic acid releases carbon dioxide gas at decompression:
H2CO3 → CO2 + H2O
 

Offline JP

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Why does beer froth up when poured into a glass?
« Reply #2 on: 14/07/2009 05:44:31 »
In addition, the reason the head stays on the beer once it forms (due to C02) is because of the chemicals in the beer, in particular the proteins from the grains.
 

Offline dtootill

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Why does beer froth up when poured into a glass?
« Reply #3 on: 15/07/2009 23:56:38 »
But can or do those who make down-market beers actually pump in CO2 from gas manufacturers, as for Coca Cola?
 

Offline Edster

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Why does beer froth up when poured into a glass?
« Reply #4 on: 22/07/2009 02:13:54 »
Bottled "real beer"  should be live, to be real beer. It normally says "bottle conditioned" and has at least a haze of live yeast in the bottle.

Many popular real ales have a bottled version which is not "live" but has been pasteurised. however carbonation levels are quite low, and similar to to a settled barrel so that beer tastes very similar to its draught natural equivalent.
( somewhere else on this site there is a Question about soda water having a taste when pure water has none  if I remember correctly)

Most quality  beers even those brewed by lagering  ( low temperature extended fermentation ) from Czech and German sources have low levels too.

The British fizz called lager has not been lagered at all, but is  still called this. These impostors contain a proportion of  adjuncts rather than pure ingredients and could not be sold in germany as the "food " has been adulterated by foreign substances like rice, maize and others , which raise alcohol more cheaply than malted barley but have very little addition to taste. They do however leave certain remnants of proteins which act as congeners and cause bad hangovers. pure beers do not unless you are allergic or have overdone it and become dehydrated.

Several of the well known brands ( I cannot say which ones in cans or keg, but my information is that a number  are brewed in Wales, for example as per oz and james`s prog where they refused cameras so I leave you to work it out) are HGB`d, high gravity brewing to over 12% ABV  using specially developed yeast to be stronger than barley wine. ( have been told 17+ but that is like a hock yeast not an evolved  beer yeast)
 This beer concentrate is then diluted with carbonated water to the more common gravities, and fizz levels associated with some very TV advertised "beers" (i use the term with maximum irony).

Live beer is very lively like champagne sometimes on opening but it it has a taste exceeding the pasteurised version and quickly calms down.

Yes mass market tv ad widdle is injected with CO2 fizz and sometimes soda water!

Oh well my hayfever may have kept me awake, but perhaps I have done something useful!
« Last Edit: 22/07/2009 02:16:10 by Edster »
 

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Why does beer froth up when poured into a glass?
« Reply #4 on: 22/07/2009 02:13:54 »

 

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