Why does nose-oil make the foam go away?
April 21, 2011 3:42 PM   Subscribe

Why does nose-oil eliminate the foam from carbonated beverages?

If you've gotten a badly poured beer at a kegger, or an overflowing coke with ice, you may know this trick- rub your nose with your finger (on the outside, natch) and then dip your finger into the foam on top- the foam starts to quickly react and shrink. Why?
posted by jenkinsEar to Science & Nature (4 answers total) 7 users marked this as a favorite
Best answer: "Dr. Barry Swanson, professor of food science and nutrition at Washington State University, says that, when you pour a beer, rapidly expanding carbonated bubbles rise to the top, grabbing proteins on the way. The proteins gather at the surface to form pockets of carbon dioxide, otherwise known as foam.

Beer foam sticks around (unlike, say, soda foam) due to the presence of carbohydrates, which stabilize it. Dark, thick beers have more carbohydrates. “That’s why a Guinness has a thick, creamy head, while a pint of Budweiser possesses a layer of thin, quickly dissipating foam.”

The introduction of oil reduces the surface tension of the bubbles, causing them to collapse and the foam to disappear. “You don’t need very much oil. You could spray the foam with nonstick Pam, or even add a drop of butter or olive oil—like you’d do to keep boiling pasta from sticking together—but that’s probably not a flavor you want,” Swanson says.

Stirring the foam with a nose-swiped index finger will get the job done, but it’s not the best idea. “You could be contaminating the beer with staph bacteria or who knows what else. The best removal method is to blow off the foam or run a knife across the top of the pint glass.”

posted by sharkfu at 3:43 PM on April 21, 2011 [1 favorite]

The oil just reduces surface tension.

More about head retention.
posted by elsietheeel at 3:50 PM on April 21, 2011

When I lived in the NE, a couple of times I drove up to New Hampshire during maple syrup season, so as to buy syrup directly from a farm where it was produced.

The sap from the trees is sweet but nothing like as thick as you'd expect. It has to be boiled in order to drive off water and get the specific gravity up to spec. So they do this in huge stainless steel tanks, with sap dripping in constantly.

It builds up foam. To get rid of it, the guy will take a knife with just a bit of butter on the end of it, and wave the tip of it through the foam. And when he does, all the foam in the entire tank will collapse almost instantly. It's amazing to see.

Not damned much butter melts off that knife, but because the oil has no surface tension it spreads out rapidly and covers the entire top of the boiling syrup. And it takes a few minutes before it starts foaming up again.
posted by Chocolate Pickle at 7:21 PM on April 21, 2011 [2 favorites]

Best answer: The introduction of oil reduces the surface tension of the bubbles, causing them to collapse and the foam to disappear. “You don’t need very much oil.

I have my doubts about this explanation of the mechanism by which the foam is reduced.

Lasting foam forms in the first place because a compound or compounds in the beer act as surfactants and reduce the surface tension of the water. Foam can also form on carbonated water with no surfactant, but the bubbles pop almost instantly because surface tension without surfactant is so great the water is pulled out of the bubbles to shapes with less surface area (spherical droplets with no interior cavity) very rapidly, and these droplets merge with the main body of water.

In bubbles, the hydrophilic ends of surfactant molecules are in the water of the bubble and the hydrophobic end is sticking up into the air on the outer surface and into the carbon dioxide on the inner surface. I think the oil actually draws the surfactant out of the bubbles into an emulsion of the oil in the water because the hydrophobic end of the surfactant is more attracted to the oil than it is to air or carbon dioxide.

This loss of surfactant causes surface tension in the bubbles of the foam to increase, not decrease, and the bubbles pop rapidly the way the bubbles in sparkling water do, and the foam disappears.
posted by jamjam at 12:39 AM on April 22, 2011 [1 favorite]

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