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Name: Unknown
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993


Question:
A 9-year old boy would like to know why root beer foams so much more than other soft drinks. He noticed that not only is there more foam, but also that it takes longer to go away.



Replies:
You might want to check out an issue of Physics Today several months back that discussed the foam in regular beer. I think in the case of root beer they put stuff in to make it foam like real beer... The scientific study of foam has only recently been underway, but brewers and other similar types have been experimenting for years to get what they wanted - think of shaving cream, for example, which was pretty much the way it is today without much help from theoretical scientists, though certainly experimentalists were involved. A foam is really a rather peculiar kind of material - it is formed by a liquid with "surfactant" molecules in it, which lower the surface tension so much that the liquid actually likes to be spread out over a really wide area, and so you can whip or stir it up so that air gets into it, forming millions of bubbles. Different types of foam have different sizes of these bubbles, resulting in different overall stiffness (I guess there are maybe other factors involved too). Eventually, gravity wins out and the liquid in the bubbles gradually drains away. Also bubbles gradually merge, getting bigger and bigger, and the foam loses its "foaminess" and disappears. These different properties - the size of the bubbles, the surface tension and complex molecules involved, and the effects of gravity, all combine to produce the quite different collection of different types of foams around. But, I am afraid I do not know the direct answer to why root-beer foams last longer. You might want to check the different ingredients used.

A Smith



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