Volume 93 Issue 11 | p. 34
Issue Date: March 16, 2015 | Web Date: March 13, 2015

Periodic Graphics: The Chemistry Of A Pint Of Guinness

Chemical educator and Compound Interest blogger Andy Brunning explores the famous beer’s bubbles and bitterness
By Andy Brunning
Department: Science & Technology
Keywords: Guinness, stout, hops, carbonation, nitrogen, bubbles, glass, pint, melanoidins, humulone, St. Patrick’s Day
 

Periodic Graphics is a collaboration between C&EN and Andy Brunning, chemistry educator and author of the popular graphics blog Compound Interest. To see more of Brunning’s work, go to compoundchem.com. Check out all of C&EN’s Periodic Graphics here.

To download a pdf of this article, visit http://cenm.ag/guinness1.

 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Comments
Dwight Matthews (Tue Mar 17 13:30:10 EDT 2015)
Could you provide references for the proposed melanoidin fragments? What I have seen so far is hand-waving discussion in reviews without specific substance.
Andy Brunning (Wed Mar 18 16:10:13 EDT 2015)
Sure! The fragment structures shown were taken from 'Food - The Chemistry of its Components' by Tom Coultate, which itself cites 'The Maillard Reaction in Foods & Medicine' by R Tressl et al. as the source of the proposed structures. There's another paper by the same authors here which details some of their proposed structures: http://pubs.acs.org/doi/abs/10.1021/jf970973r
Ashar (Tue Mar 17 15:44:14 EDT 2015)
Very nice and informative
SHUAIBU Abubakar. (Tue Mar 17 16:23:58 EDT 2015)
Found very interesting!
Fina Guitart (Tue Mar 17 18:20:18 EDT 2015)
Is the most bear foam caused by nitrogen or carbon dioxide? The information in the written text is not agree with the % of both gases. Is there any mistake? Thanks a lot!
Andy Brunning (Wed Mar 18 15:53:20 EDT 2015)
The 'most beer foam' refers to other beers, not to Guinness. So whilst most beers will use carbon dioxide for carbonation, Guinness uses a blend of carbon dioxide and nitrogen, in the proportions shown. Hope that clears up the confusion!
Don Hoernschemeyer (Thu Mar 19 12:13:45 EDT 2015)
Delightful article. My granddaughter did not like beer until she visited Ireland and tasted Guinness Stout; now she is a fan of it - in moderation of course.
» Reply
Robert Buntrock (Tue Mar 24 16:53:36 EDT 2015)
I'm curious why the use of nitrogen in addition to CO2 reduces the bitter taste somewhat. Given the inertness of N2 I would assume that it's due to dilution of the acidic CO2. Could this be verified? As stated, N2 obviously helps with the signature effect of the bubbles.
Lance Lusk (Wed Mar 25 16:03:28 EDT 2015)
The amount of foam is less important than the foam stability. If you enjoy beer foam, you would be disappointed with a Sprite-type rapidly collapsing foam. Nitrogen foam lasts longer because there is less gas loss from the bubbles to air because air already contains 78% nitrogen. The bubble gas will try to reach equilibrium with the gas in the atmosphere. As for bitterness, the hop compounds that create bitterness concentrate in foam along with select beer proteins. Lick the foam and then take a sip of beer for comparison. Nitrogen bubbles are smaller offering more bubble surface area for the bittering compounds to concentrate. And because the bubbles collapse more slowly, more bitterness remains in the foam rather than returning to the beer.
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