John Vor (126.96.36.199)
|Posted on Tuesday, May 06, 2003 - 09:11 pm: ||
I recently read an article about Harp(?), the company that makes Guinness
I think, using "laser aging", some method of post-bottling processing.
They expose the bottles to an intense laser, which does not harm volatiles
as sunlight does. I cannot find this article (I want to say it was
Popular Science) and it is driving me crazy. Everyone I ask gives me a
blank stare, but this is real. I figure if anyone would know it would be
you guys, or do you know anyone else to ask?
Of course I want to try this laser-aged beer, but I am more interested in
what that process actually -does-. I remember the end result was a finer
carbonation, but it makes no sense to me.
Bryin Tugade (188.8.131.52)
|Posted on Friday, March 19, 2004 - 08:02 pm: ||
I dont know if anyone is reading this a year later, but I think I found the answer.
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.
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'C 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 gas 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.