Learned this “tip” in college when there just wasn’t enough hours in the day to wait for a beer’s head to die down.
Pour a beer such that you get a thick head. Take your finger and rub the tip along the side of your nose–get some oil on it. Now swirl the tip of your finger around the top of the foam.
Why does that happen?
The oil on your finger breaks the surface tension of the beer foam. This lets the CO[sub]2[/sub] to escape. I could be wrong of course 
Yeah, but you could have… like 5 inches of foam. All you have to do is swipe your finger once across the foam and it’s all gone in 30 seconds!
Stick your finger in the beer?
Who’s reminded of Joe the Bartender?
A shake of salt will also reduce head.
surface tension
n.
A property of liquids arising from unbalanced molecular cohesive forces at or near the surface, as a result of which the surface tends to contract and has properties resembling those of a stretched elastic membrane.
A measure of this property.
okay, so I’m not a sudsologist, but I will give this the best shot I can.
Foam is the result of some type of detergent or surfacent, which has two bonding abilities. On one side is a hydrophobic (oil-bonding) area, and on the other is a hydrolipic (?) (water-bonding).
Suds are hydrolipic outside, hydrophobic inside. That’s why greases and skin dirts are carried away by soaps. I’m guessing the nose-grease technique (which also works well with forehead secretions) causes the structural integrity of the suds to give out, what with lots of oil outside the suds.
who knows, really? and by the way, if anybody knows the big dirt on this scoop, feel free to correct or amend any of the above.
There is a whole class of chemicals known as defoamers. They’re used in all kinds of industrial processes to break down foam that builds up when you agitate certain mixtures. They’re usually active in pretty tiny amounts. I used to deal with them when I made paint, because foam in paint can really get out of hand without a defoamer. If you want to know how they work, get a book on surfactant chemistry and read the chapter on defoamers. It will probably say something like, “No one really knows how defoamers work, but one theory is…” and then it will say something completely incomprehensible. To me, anyway. YMMV
I took a bartending class given by the local Budweiser disributor. He said that foam is supposed to be there.
If you pour so there is no foam it is released in your stomach. belch or worse!!!
Too much foam is not appreciated by your customer.
A glass of beer is supposed to have about 1/2 inch of foam.
Also that foam that sticks to the side of the glass—It shows that the glass was beer clean.If it doesn’t stick send it back.
Sticking your finger in the glass is a little unsanitary and maybe even disgusting,especially if you have body secretions on your finger.If you re outside just blow across the top of the glass.