Guinness FAQ and Folklore
(c) Alan Marshall archive name: beer-guinness.faq
ak200032@sol.yorku.ca Revised, March 16, 1995
There has been much posted about Guinness to this group, and much
of it could be used to spawn a new group alt.guinness.folklore. I
find a great deal of irony in this: there is probably more
"folklore" about Guinness than any other beer, yet it was the
Guinness people that underwrote the famous "Book of Records" to
settle arguments often based on rumours rather than fact. So, in
an attempt to "set the record straight" I offer:
Guinness FAQ and Folklore
Contents:
I. Guinness Facts
II. Guinness FAQs
III. "Black and Tan" FAQs
IV. Guinness and Health
V. Specifications of the Various Types of Guinness
Appendix I -- A guide for the un-initated to buying Guinness
in an Irish pub.
Appendix II -- Patent Information on the Smoothifier
I. Guinness Facts
~References: MJBC -- Michael Jackson's Beer Companion (1993)
MJPG -- MJ's Pocket Guide to Beer (1991, 1994)
RADA -- Real Ale Drinker's Almanac (Protz)
"No other brewery uses as much roasted barley as Guinness, which
prepares its own." (MJBC, p 181)
"The brewery...uses several varieties (of hops), among which
Goldings are perhaps the most influential." (MJBC, pp 180-181)
Guinness "...uses its original yeast, though this has been selected
down from several strains to one, which was arrived at in about
1960. It works at high temperatures (around 25'C/77'F), and it is
very dispersed, having neither risen to the top nor sunk to the
bottom, when it is removed by centrifuge." (MJBC, pp 181)
"Dublin makes five or six principal versions of Guinness, in a
total of 19 variations, and exports around 40 percent of its
output." (MJBC, p 181)
All the grain used by Guinness is grown in Ireland. The non-malt
grains used in the domestic product is 25% flaked barley and 10%
roasted barley. (MJBC p 181)
II. Guinness FAQs
Q: I've seen Guinness sold in Germany even when the
Reinheitsgebot applied to imported beers. How can that be?
A: "In line with the German Purity Law, the barley is replaced
with pale and roasted malt in Continental Europe." (MJBC p
181)
Q: What types of Guinness are there?
A: Michael Jackson states that there are 5 or 6 main types in 19
variations. So far, we've been able to identify (Detailed
specifications are listed in the last section of this FAQ):
Draught Guinness (Ireland, NA), is smooth full-bodied and
creamy. Despite its body, it is a rather mild beer (OG
1039, 3.4% abw, 4.2% abv). This beer is pasteurized.
There are many local variations of this product. The
canned "Pub Draught Guinness" using the draught-flow (tm)
system is a packaged version of this beer.
Bottle Conditioned Guinness (Ireland) had similar
specifications to the Draught Guinness, but the presence
of the yeast provides for a "...spicier, fruitier, drier,
more complex and lively, fresh character." (MJBC, 182)
Bottled Guinness (Britain) has similar specifications to the
above two beers, but it is pasteurized.
All Malt Guinness (Continental Europe) is available both
draught and bottled. It is slightly stronger and also
has a little more of the characteristic stout bite.
Guinness Extra Stout/Guinness Original (bottled, available
widely) is stronger with even more stout bite. MJ
reports this to be 4.8% abw, 6.0% abv, but one poster
says that in advertising from Guinness Imports, the
strength is listed as 5.6%. This product is licensed for
production widely around the world.
There is a strong bottled version (Belgium and others) that is
somewhat sweeter and stronger (7.5% abv)
Foreign Extra Stout (primarily tropical countries) is also
about 7.5% abv. However, this is blend of Guinnesses,
included one aged for three months.
In Nigeria, which bans barley, Guinness is made from sorghum.
Q: What is a Black and Tan?
A: Guinness (or some other stout) mixed with another lighter
coloured beer such as a pale ale or lager. There is now a
separate section of this FAQ on Black & Tans.
Q: What is Black Velvet?
A: Guinness and Champagne in equal proportions (MJBC p 176)
Q: Are there other Guinness drinks?
A: A poor-man's Black Velvet is Guinness and cider. There are
several variations involving black current cordial or cassis.
Cordial will sweeten a Guinness, and if poured in through the
head, leaves a purple "splotch" in the head. A Purple Meany
is half Guinness, half bitter (the dregs of the cask if
possible) and cordial. (No thanks to Niall McAuley and Duncan
Snelling for these horrible drinks!)
Q: I once saw shamrocks on a Guinness. What that all about?
A: This was started back in around 1988 or so for the benefit of
tourists. Susan Hoban, author of "Irish Pubs Across America"
- A guide to over 300 Irish pubs in the U.S., writes: "In
fact, one will encounter many a shamrock atop a pint of
Guinness in America, made by the bartender 'drawing' the
shamrock at the end of 'drawing' the pint."
Q: How does the draught-flow can work? What's that plastic thing
in the can do?
A: The simple, non-technical answer is that the little plastic
bladder is filled with nitrogen, not nitrous oxide or nitrous
dioxide as claimed by a couple of posters. Since the can's
contents are under pressure, some of the Guinness is forced
into the plastic bladder through a pin-hole. When the can is
opened, the nitrogen and beer mixture is released creating the
lovely foamy head.
Nitrogen is used because it creates smaller bubbles than
carbon dioxide, which can also leave a tinny taste.
Q: Where can I get more detailed information on this?
A: Here. Thanks to Joel Plutchak, who saved this information
that someone else (unattributed) posted. (I would be happy to
give credit to the original poster -- email me)
"The problem has always been the fact that draught Guinness is
(or should be) dispensed with a mixture of Nitrogen and CO2
gasses rather than the conventional CO2 alone. The nitrogen
is used because it makes very fine bubbles while it is not
absorbed into the brew as the CO2 is, thus it does not
"over-carbonate" the beer. Also a special faucet is preferred
which, in combination with the gasses, creates that wonderful
creamy brown head which lasts to the bottom of the glass. The
new can combines the original kegged stout recipe with
technology which creates the draught effect to a tee.
"Dr. Alan Forage, creator of the technology, was on hand to
explain the mechanics of the new can. This is the way the
system works: The 16.9 ounce can (containing 14.9 ounces of
beer) is fitted with a small plastic device (Guinness calls it
a "smoothifier") which sits in the bottom of the can. This
device has a pocket or cavity which is open to the atmosphere
via a pin hole in its top. The can is evacuated of oxygen and
filled with beer. Prior to sealing the can, a dose of liquid
nitrogen is added to the beer. The can is closed and as the
liquid nitrogen warms a pressure is created. The pressure
forces about 1% of the beer and nitrogen into the plastic
cavity. When the can is opened, the pressure is released and
the small amount of beer in the cavity is forced back through
the pinhole quite violently. The agitation created by this
"geyser" mixes the nitrogen with the beer in such a way as to
reproduce the tap handle character. Open up the first empty
can you have in order to see what the "smoothifier" looks
like."
Technical details from the patent are in Appendix II.
Q: Why does the bottled Guinness taste so different than the
draught or canned "draught-flow" product?
A: (U.S./Canada answer): These are two entirely different beers.
The bottled Guinness if Guinness Extra Stout, while the others
are simply Guinness. The Extra Stout uses more roast barley
and has somewhat higher IBUs, resulting in a harsher, sharper
flavour. Which you prefer is a matter of personal taste.
(Ireland answer): The bottled product is bottle conditioned,
meaning the presence of live yeast. The yeast gives it a very
different character.
Q: What's the significance of the harp symbol on Guinness
products?
A: Arthur Guinness & Sons deliberately chose the harp symbol as
its logo or symbol to appeal to nationalist pride in Ireland.
The harp is also a symbol of Ireland, which appears on the
back of their coinage. The Irish Government and Guinness
versions of the symbol are identical, except for the fact that
the Guinness Harp faces left, while the official government
version faces right.
Q: What products besides the various Guinnesses does Guinness
produce?
A: Arthur Guinness & Sons also own and produce Smithwicks
(pronounced without the "w"), also sold as Kilkenny, Harp
Lager and Macardles ales. In England they also market
"Guinness Draft Bitter" which uses the same draught-flow
system and Guinness stout.
Q: Is there anything I need to know when I go into a pub for a
Guinness?
A: First, you don't "go into a pub for a Guinness". A bird
doesn't fly with one wing! You always have two! One of the
classic posts to the r.f.d.b newgroup was Alan Clinton's "A
guide for the un-initated to buying Guinness in an Irish pub."
It is reproduced in Appendix I.
Q: What do the numbers on the Guinness labels mean and why isn't
there a set of numbers on the Pub Draught (tm) cans?
A: We are still looking into this, but we believe there are
licence numbers for the different styles of Guinness.
ejoynt@whoi.edu (Ernest H. Joynt, III) offered the following
information:
Guinness Extra Stout (purchased in the US)
L/A1 821212
Guinness Foreign Extra Stout (made in Trinidad)
L/AU 771712
Guinness Special Export Stout (8.0% abv, made in Dublin)
A/RM 571012
The letters and numbers preceding the six-digit number are
actually written with the first letter over the other two.
For example, the Guinness Extra Stout is "L over A1".
The Pub Draught Guinness (tm) does not have this type of
numbering on the can. We do not know why.
Q: Is the Guinness family still involved with the Guinness
company?
A: The family still has a large financial stake in Arthur
Guinness & Son PLC, but have not been directly involved in the
management since 1992.
Q: Why are there so many Irish pubs springing up?
A: Well, there are two types of people in this world: Those who
are Irish, and those who want to be!
In fact, Guinness has set up a business that will totally
outfit and "Irish Pub" for a would-be publican. All the
publican has to to is provide the site. In Germany, they are
opening at the rate of about 4 per week.
Q: Someone told me that Guinness intentionally added sour
Guinness to their beers. Is that true?
A: Yes, part of the process is to blend in some specially soured
Guinness. The following was extracted from the Homebrew
Digest. I believe the original author was Martin Lodahl, but
I may be mistaken:
"...they have a series of huge oaken tuns dating back to the
days before Arthur Guinness bought the brewery, which they
still use as fermentors for a fraction of the beer. The tuns
have an endemic population of Brettanomyces, lactic acid
bacteria and Lord knows what else, and beer fermented in it
sours emphatically. They pasteurize this and blend small
quantities of it with beer fermented in more modern vessels."
Q: I've heard that Guinness contains oysters. Is that true?
A: No. At one time, oyster shell may have been used as finings
to rid the beer of unwanted solids, but this was not in this
century, and may not have ever been done by Guinness. There
are oyster stouts that contain oyster, oyster extracts, etc.
Q: Doesn't Guinness contain oatmeal?
A: No. It is a rather common misconception that Guinness (and
all other stouts) contain oatmeal. Oatmeal Stout is a
distinctive style stout. The revivalist of this style was
Samuel Smith's Brewery in Yorkshire, England, at the request
of its North American agent, Merchant du Vin of Seattle.
Q: How does one spell Guinness?
A: Never! That's a waste of nectar! Oh, Sorry. I thought you
said "spill".
Guinness is spelled exactly as you see in the question -- two
"N's", two "S's" and a "U" before the "I". The "G" is always
capitalized out of reverence. Unfortunately, it is misspelled
in the index of the 1991 Pocket Guide to Beer (only one "N").
Q: Doesn't Guinness contain {insert name of animal} {insert your
favourite word for urine}?
A: No. It is not part of the formulation, and there is virtually
no opportunity for this to happen by chance. We cannot be as
unequivocal about Labudmilloorsons, however. ;-)
Q: What's the proper thing to say when someone {buys you a
Guinness/ gives you a 4-pack of Draught-flow cans/gives you
your own cask}?
A: Whale oil beef hooked! ;->
Q: Is there a Guinness smiley/emoticon?
A: (:-{d) (licking the rich, creamy Guinness foam off the upper
lip.)
III. "Black and Tan" FAQs
Q: What is a Black & Tan? What is a Half-and-Half?
A: The answer depends on who you ask. The all-Guinness Black &
Tan is Harp Lager and Guinness. (Harp is brewed by Guinness
at Dundalk). Many consider the classic Black & Tan to be Bass
Pale Ale and Guinness. (To some Irish, they appreciate the
fact that the Irish comes out on top!) However, Bass Ale is
not as available in Ireland as it used to be, and either Harp
or Smithwicks is generally used. However, there are many
variations involving a stout or porter and another lighter
coloured beer, either lager or ale.
A half-and-half is often just another name for a Black & Tan.
However, in many North American Irish pubs, the Bass/Guinness
combination is called a Black & Tan, while the Harp/Guinness
combination is called a Half-and-Half.
To quote Brendan E. Molloy (b.molloy@ic.ac.uk):
According to "The Guinness Drinking Companion" by Leslie
Dunkling:
Black and Tan = Guinness and Mild
Half and Half = Mild and Bitter
The above book (now sadly out of print) was published by
Guinness Publishing and if anyone knows they do! The
full Oxford English Dictionary also mentions these
mixtures (look under Beer, Ale, Drink, etc.).
With the decline of Mild in the UK these names are
dropping out of use. In Dublin, where Mild is no longer
available, you will get Guinness mixed with Bitter if you
ask for a Black and Tan. Some publicans serve other
combinations so it is best to check before you buy.
Note: Mild is a slightly sweetish 'Tan' coloured beer, that
is typically light in alcohol.
However, Guinness promotional advertising in the U.S. refers
to a Black & Tan as being the Bass and Guinness version. Ken
Papai described the ads as follows:
Here is the Guinness Import Company (c) 1992 ad on their
beer card/beer coaster that they distribute at pubs and
beer shows:
THE TRUE COLORS OF HALLOWEEN (picture of black & tan
in a pint glass)
Guinness (picture of a harp, the
Guinness trademark and
logo)
Bass Ale (Bass logo)
BLACK & TAN
It should be noted that Guinness Imports Ltd., also imports
Bass Ale.
So, Black and Tan, Half and Half, B&T, Half'n'alf, it all
depends on where you are and who you ask. When your bartender
is a 240 lb., 6'4" fellow named O'Malley, a Black & Tan (or a
Half-and-Half) is whatever he says it is!
Q: How do I pour a Black and Tan?
A: Steve Glover, who has tended bar in Ireland, says that the
layered Black and Tan is an American affectation that they
were happy to do for extra money :-). Otherwise, both beers
(they used Smithwicks and Guinness) were simply poured in the
same glass fully mixed.
If you want a layered drink: Carefully. Practice. With a
special spoon. There are many answers.
I have had success pouring the Harp or Bass vigorously so that
it develops a good head. Using a Black & Tan spoon, pour the
Guinness slowly over the back of the spoon. It will remain
layered for some time. (You can make your own by bending the
bowl of a spoon back so that when you lower it into the glass,
the bowl is concave down.)
The Guinness promotional beer coaster cited above offers the
following advice:
HOW TO POUR A FRIGHTENLY PERFECT BLACK & TAN
1. Hold your pint glass at an angle, and fill just
over halfway with Bass Ale on tap.
2. Slow the flow control on the Draught Guinness tap
down to a trickle.
3. Fill to the top, letting Draught Guinness hit the
side of the glass.
or...
Pour Draught Guinness over an upside-down spoon to
disperse the flow.
4. Let settle, and enjoy the True Colors of Halloween!
Q: Why does the Guinness float on top of the other beer?
A: "Quality always rises to the top" (Jon Binkley)
Tom Otvos (tomo@everyware.com) offers the following
hypothesis:
I have sometimes wondered about why the Guinness stays on top
of a layered Black and Tan myself. A friend of mine and I
(both of us engineers) came to the conclusion that the SG of
Guinness is not appreciably different from other beers, but
that it is the higher viscosity of the liquid that prevents if
from mixing. We assumed that it was this viscosity that gives
Guinness its body, and the perception that it is a "heavier
beer".
David B. Sapsis sends this
hypothesis:
I am virtually certain that although the very high protien
content of this brew (what do you expect from a grist thats
25% flaked!) does in fact make it more viscous, and this is
born out in mouthfeel, the driving force behind Guinness
floating on other beers is differences in density. Not only
is Guiness very well attenuated (I have degassed Pub draft and
found its gravity to be 1009) it is also usually served quite
a bit warmer than the "bottom half". Thus, an ale served
around 40F is at the peak of its density tempertaure curve
(max rho at 4C) and is likely to have a higher finishing
gravity, both raising the delta rho. Now I do believe that
the initial boundary layer formation is highly viscocity
dependent, because ... if you overpush the stout, you can
break the boundary and mixing results.
Q: Is there any meaning to the Black & Tan name other than its
obvious reference to the colours of the beers?
A: Yes. The first known reference to the expression Black & Tan
was in reference to a breed of beagles used as hunting dogs in
Ireland. The term was also used to refer to a a regiment of
British soldiers recruited to serve in Ireland after the First
World War. They had a reputation for being quite brutal and
have been accused of many attrocities against the Irish in the
years 1919-21.
Q: Should I order a Black & Tan in Dublin?
A: Some have posted that this is not advisable, as you might stir
up tempers. Steve Glover and others post that ordering a
Black and Tan is no problem.
Q: Is there a Black & Tan Song?
A: Thanks to J. N. Walsh, we can offer you:
Come Out ye Black & Tans!
-------------------------
I was born on a Dublin street
Where the loyal drums did beat
And those bloody English feet
They walked all over us!
But every single night
When me Da would come home tight,
He'd invite the neighbours out
With this chorus:
Come out ye Black & Tans!
Come out and fight me like a man.
Show your wife how you won medals
Down in Flanders.
Tell her how the IRA
Made you run like hell away
From the green and lovely lanes
Of Killeshandra!
Q: In another newsgroup, someone asked if Black & Tans were
invented in the U.S. Is this true?
A: Wasn't everything worthy and of good repute, including
justice, honour (sorry, honor) and civilization invented in
the U.S. of A.? ;-)
IV. Guinness and Health
Q: Is Guinness really "good for you"?
A: Medically, possibly. Its alcohol is low enough to have a
relaxing effect. The bottle-conditioned product may produce
a mild laxative effect due to the live yeast. Too many
bottles of the bottle-conditioned product can have an extreme
laxative and diuretic effect, which is not good for you.
There is medical folklore about Guinness and stout, in
general. "In some countries, stout is seen as an aphrodisiac,
or as a beneficial bath for newborn babies." (MJBC p 177)
Since most research indicates the aphrodisiac effects are
primarily psychological, there may be truth to the former.
Too many may have an adverse affect on performance, however.
Of course, if you feel as good as I do after enjoying and
Guinness, then there is no question that it is good for you!
Q: But isn't Guinness high in calories?
A: Not especially. "Guinness is not notably high in calories..."
(MJBC, p 177) This refers to the draught, bottle-conditioned
and draught flow (tm) product, which are fairly low in
alcohol. Calories in beers come from the alcohol and the
residual sugars. The higher the alcohol, the higher the
caloric content.
Q: Where did the "Guinness is Good for You" come from?
A: Guinness's advertising agency (S. H. Benson) did some market
research during the 1920's to find our what people liked about
Guinness. People responded that they felt good when they had
their pint and the slogan was born. The slogan is still used
in some countries (notably in Africa) that do not regulate
advertising claims as zealously as the U.K. and North America.
Some have even posted that the advertising features athletes
and imply that there athleticism can be attributed to
Guinness.
Q: Guinness has been dispensed in hospitals, correct?
A: Yes. In England, post-operative patients used to be given
Guinness, as were blood donors. Sadly, this is no longer the
case in England. In Ireland, Guinness is still made available
to blood donors and stomach and intestinal post-operative
patients.
Q: What about the old wives' tale about nursing mothers drinking
Guinness?
A: Current medical research suggests that pregnant women and
nursing mothers should totally abstain from any form of
alcoholic beverage. In pregnancy, it can lead to Fetal
Alcohol Syndrome, characterized by slow development. Alcohol
does pass in the mother's milk, so nursing mother's should
avoid Guinness and any other form of alcohol.
Q: Guinness is high in vitamin G, isn't it?
A: There is no vitamin G! However, the folklore surrounding
Guinness has often lead to it being called vitamin G.
Recommended Daily Allowance: 3 pints a day.
V. Specifications of the Various Types of Guinness
Draught Guinness (Ireland & North America):
OG: 1039 (9.75 Plato)
Alcohol: 3.4% abw, 4.2% abv
BU: 45
Colour: EBC - 130
"Draught-flow" Canned "Pub Draught Guinness"
Similar specifications as the Draught Guinness, above.
Alcohol: 3.3% abw, 4.1% abv
Bottled Guinness (U.S.) -- This is an "Extra Stout"
Alcohol: 4.8% abw, 6% abv (Although one poster noted that they had
seen 5.6% in their promotional materials. Michael Jackson
reports these figures.)
BU: 50+
Continental Guinness (Draught and bottled)
Alcohol: "a little more than 4 percent by weight, 5 by volume"
(MJBC p 181)
"strong" Bottled Guinness
OG: 1073 (18 Plato)
Alcohol: 6% abw, 7.5% abv
BU: 50+
Guinness Extra Stout (England, according to Eckhardt)
OG: 1052 (13.2 Plato)
Alcohol: 4.4% abw, 5.5% abv
BU: 50
Colour: 9.5 (Eckhardt's Scale) This would translate into
something around or over 50 SRM and about 130 EBC
Guinness Extra Stout (Ireland, according to Jackson)
(bottle conditioned)
OG: 1039 (9.75 Plato)
Alcohol: 3.4% abw, 4.2% abv
Bottled Guinness (Ireland)
"similar" specifications as Draught Guinness
OG: 1040
Alcohol: 3.5% abw, 4.3% abv
Contents: Pale malt, flaked barley, roasted barley, English and
American whole hops (RADA)
Note: This may be the same beer as the previous listed
entry.
Foreign Extra Stout (this is a blend of Guinnesses):
OG: 1073 (MJPG91)
BU: mid-60s
Guinness Extra Stout (Ireland in 1901, according to Eckhardt)
OG: 1075 (18.2 Plato)
Alcohol: 6.3% abw, 7.9% abv
BU: 90 (!)
Appendix I
A GUIDE FOR THE UN-INITATED TO BUYING GUINNESS IN AN IRISH PUB.
1. Choose your pub carefully. A pint of Guinness does not
appreciate loud music, loud people or bright flashing lights.
2. Ask politely for a pint of Guinness. Depending on the pub, it
is possible to catch the barmans eye and mouth the word
"pint", he will translate this accurately.
3. The barman will fill the glass between 70% and 80% capacity.
It will then be put to the side for a few moments to allow it
"to settle". Once the brownish liquid has almost turned to a
solid black the barman will then fill the rest of the glass.
NB: do not under any circumstances take the glass before it is
filled. Some virgins seem to think that the settling stage is
the final stage and walk away with an unfinished pint. At this
point we Irish DO understand the predicament, but I assure you
it causes endless mirth as well.
4. Once you have received your pint, find a comfortable stool or
seat, gaze with awe into the deep blackness, raise the pint to
your mouth and take a large mouthful. Be firm.
5. A good pint can distinguished by a number of methods. A
smooth, slightly off- white head is one, another is the
residue left on the inside of the glass. These, surpise
surprise, are known as rings. As long as they are there you
know your're okay. A science of rings is developing - the
instance that comes to mind is determining a persons
nationality by the number of rings (a ring is dependent on a
swig of Guinness each swig leaving it's own ring). An Irishman
will have in the region of 5-6 rings (we pace ourselves), an
Englishman will have 8-10 rings, an American will have 17-20
(they sip) and an Australian won't have any at all as they
tend to knock it back in one go!
6. As you near the end of your pint, it is the custom to order
another one. It is a well known fact that a bird does not fly
on one wing.
- Alan Clinton (aclinton@dub-fdev.dub.comm.mot.com)
Appendix II
Patent Information on the Smoothifier
Robert James posted:
I was doing some patent search work at the Washington library in
Chicago the other day and I ran across no. 4,832,968, the U.S.
patent for the Guinness in a can stout. The basics:
Inventors: Alan J. Forage & William J. Byrne
Assignee: Arthur Guinness Son & Co., Ltd.
Process:
- The gas pod in the can is blow molded with nitrogen (N)
- A laser zaps a hole in the pod. (they experimented with holes
between 0.2mm and 2.5mm finding that 0.61 mm as ideal)
- Pod is inserted in the bottom of can
- Can is filled with CO2/N supersaturated stout. N is present
at 1.5% v/v min up to 3.5% v/v. (FYI, vol/vol is the number of
volumes of gas which are dissolved in a unit volume of
beverage at 760mm of Hg & 15.6 oC) CO2 is present at between
0.8 and 1.5% v/v.
- During filling, foam rises to top of can. This clears the
air.
- A charge of liquid N is added to the stout
- Can is sealed
- As liquid N boils off in can during pasteurisation (60 oC for
15-20 min), top of can pressurizes and forces the stout into
the pod, thus compressing the ambient pressure N in the pod.
- Equilibrium is reached at about 25 psi
As I interpret the patent, this is what happens when the can is
opened:
The can quickly depressurizes to ambient pressure. The pod thus
expels the stout contained in it (about 10-15 ml) at high velocity
through the orifice. This causes high local strain of the stout at
the plane of the orifice. This strain exceeds the cohesive forces
holding the gases in solution. As a result, the N/CO2 is liberated
from the stout at the plane of the orifice.
The millions of tiny N/CO2 bubbles then become the foam head. So
contrary to my initial belief, while some of the N gas in the pod
escapes directly into the stout, it is actually the "ripping apart"
of the stout as it exits the pod which produces the bubbles, hence
the creamy head.
-- Alan Marshall "It's a lot of work to get up in front of
AK200032@SOL.YORKU.CA a class and make it look like you know
York University everything there is to know about something
Toronto, Canada you know nothing about." Prof. Anonymous