My Nutrasweetened soft drinks make huge mounds of foam! What gives?

Illustration by Slug Signorino

Cecil replies:

You may not believe this, Ken, but Coke, Pepsi, and the G.D. Searle company, the maker of NutraSweet, all deny any knowledge of the foam-producing properties you describe. However, scientific tests conducted at the legendary Straight Dope labs have proved conclusively that they do in fact exist. Moreover, it is clear that not only do NutraSweetened beverages produce more foam, but the foam lasts longer. The ecological significance of this development is too awful to contemplate.

We began by comparing Diet Coke to regular Coca-Cola. Uncapping a bottle of each, we let them moulder in the fridge overnight. Next morning we poured an equal volume of each product into a pair of genuine sculpted Coca-Cola soda fountain glasses, which we got at a local hot dog parlor two summers ago. (We feel these little touches are important.) The results were dramatic. Not only did Diet Coke produce substantially more foam (in some cases two or three times as much), but the foam proved to be amazingly durable. While the regular Coke froth dissipated in a few seconds, fully two minutes went by before you could see the top surface of the Diet Coke underneath the bubbles. Moreover, even half an hour later there was still a significant amount of foam left around the edge of the Diet Coke glass, whereas the regular Coke had all boiled down to nothing. Cecil attributes this partly to the fact that the products had been chilled, since the Diet Coke head didn’t last anywhere near as long when it had warmed up to room temperature. But even when warm, Diet Coke showed more vigor than the regular stuff.

Unfortunately, we were not able to compare a NutraSweetened beverage directly with the saccharine-sweetened version of the same product, because the former have generally chased the latter out of the marketplace. However, we were able to obtain several cans of a Brand X cola that is still sweetened with saccharin. In a head-to-head (heh-heh) foam-off between Brand X and Diet Coke, the latter easily trounced its low-rent competitor. Whether this was due to the presence of NutraSweet or simply to the superior quality of Coca-Cola manufacturing is hard to say. Still, we may note that when sugar-sweetened Brand X and Coke were compared, they both fizzed out in approximately the same amount of time.

Finally, we performed the well-known “squirt” test, which consists of going out in the alley behind the house and shaking up the bottles with your thumb held over the top. The intention here was to determine which product would produce a greater volume of liberated CO2 gas — i.e., which one would squirt farthest. Unfortunately, the results were inconclusive, mainly because the damn foam got all over everything, forcing Cecil to call a halt to the proceedings while he changed his shirt. The path to progress is never easy.

Since research is still in the preliminary stages, Cecil does not feel it would be appropriate to offer a theory on the cause of Diet Coke foam at this time. In the meantime, however, the makers of NutraSweetened soft drinks are clearly missing the boat in not touting the longevity of their carbonation, e.g., “Sticks to your lips, not to your hips.” I guarantee you, sales would skyrocket.

The Teeming Millions get the right idea

Dear Cecil:

What is the protocol for when you actually respond to a reader’s quest for knowledge? I ask this because I was pleased to note that you confirmed my observation about diet Coke some weeks back. Was I supposed to call you up? Send you a present? Is there an expected bribe? I know you are not Miss Manners, but nevertheless you probably have as good a handle on the appropriate behavior in this situation as anyone.

— Anonymous, Chicago

The satisfaction of a job well done is all I require, along with $100 in an unmarked envelope by five o’clock or you’ll never get your garbage collected again. I thought Chicagoans understood things like this.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.