MadSci Network: Chemistry

Re: Why does diet coke fizz more than regular coke?

Date: Tue Oct 26 14:34:28 1999
Posted By: Kieran Kelly, MadSci Admin
Area of science: Chemistry
ID: 940718812.Ch

Interesting question!  I don't have any data to share to confirm my thoughts on 
this topic but I am sure your local library will be able to help you find some 
physical chemistry texts with explanations of surfactant chemistry or foaming...

The different types of sweeteners used in the two products is causing the 
different foaming behaviors.  High fructose corn syrup (HFCS), used in regular 
Coke, is rather syrupy or soapy and increases the viscosity of the liquid.  It 
also impacts the surface tension of the beverage but I can't remember if it is 
higher or lower (lower, I think, since soaps do the same thing).  In any case, 
foam is collapsed by causing drainage of the liquid from the lamellar region 
(thin liquid film between bubbles).  The aspartame in the diet Coke is making 
this drainage happen more slowly than the HFCS in the regular version.  The 
diet's foam lasts longer and it looks like it fizzes more than the regular.  And 
the two usually have the same amount of carbonation (assuming you opened them at 
the same time and they were at the same temperature).

You could try doing a quick comparison of surface tensions between the two at 
home:  pour a glass of each soda and let them stand out overnight until they are 
flat.  Try this surface 
tension experiment using the two sodas.  It should be easier to "float" the 
blade on one surface (the one with higher surface tension).  You can also try 
comparing your results with glasses of regular and soapy water of the same 

I hope this information helps!


Current Queue | Current Queue for Chemistry | Chemistry archives

Try the links in the MadSci Library for more information on Chemistry.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-1999. All rights reserved.