Hello I’m Daven Hiskey and today we’ve got something a little different for you.
We received a question from a TodayIFoundOut subscriber on whether or not tapping a shaken
soda can actually results in less foam spewing out, as is the widely held belief.
This seemed interesting enough to us, but when we looked far and wide for a definitive
answer, we uncharacteristically came up empty.
So we decided to run an experiment ourselves to find out the answer.
And just before we get into that, you should know this episode is brought to you by iFixit,
the free online repair manual for everything, written by everyone!
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Alright, now, to be clear, when looking at answering the question of whether tapping
a shaken can of shaken soda actually does anything, certainly there are many otherwise
reputable sources throwing out an opinion on both sides of the argument.
But outside of Snopes, nobody seems to have bothered to experimentally test whether tapping
the can does anything.
And as for Snopes, while they technically did do an experiment, this was a reported
sample-size of just three runs (although they do allude to "a variety of experiments" not
reported).
It is possible one doesn't need a large sample size here to get meaningful results, so perhaps
three runs is a perfectly sufficient sample.
However, Snopes gives no hard quantitative data (only anecdotal observations) on this
one, and did not necessarily shake each of the cans the exact same way (though did time
it and presumably the shaking was approximately the same if they had the same person shaking
each time).
But needless to say, while Snopes' conclusion may end up being perfectly correct, we weren't
really comfortable stating it as a definitive answer here given the way the experiment was
conducted and lack of hard data.
But if you're curious, their results indicated that tapping the side of the can produced
slightly less foam than simply waiting to open it, but otherwise from a practical standpoint
didn't really make a difference.
As for expert opinions, these also were conflicting, though perhaps the best such source in Cornell
University biochemist, and one of the world's leading beverage foam experts (and, yes, that’s
a thing), Karl J. Siebert, rang in on the side that at best tapping the can does nothing
in his opinion, and even potentially makes the problem worse.
As Dr. Siebert states, by tapping the can, "you risk creating more bubbles."
Despite this, many otherwise reputable sources claim that tapping the can does actually help.
Why?
As you're probably aware, when you shake the can, the agitation causes some of the dissolved
carbon dioxide in the container to form bubbles at various nucleation sites on the inner surface.
It's also further widely held that some of the bubbles formed will stick to the inside
of the container at these various nucleation sites, rather than rising to the top.
When the can is opened and the high pressure thus removed, these bubbles rapidly expand
and shoot to the top of the container, pushing out some of the liquid with them.
Thus, the hypothesis is that by tapping on the can, you can dislodge these bubbles and
cause them to float to the top before opening the container, so that when you do open the
can, the gas can expand and escape without taking any liquid with it.
Seems reasonably enough, but does this actually work?
To begin with in our little experiment, we needed a device that could shake our soda
cans exactly the same every single time.
The Shakenator T-3000 we made to do this works such that with each button press, it shakes
the can exactly 10 times with a stroke length of 1.125 inches or 2.9 cm.
Through a bit of experimentation, we ultimately found that at our coldest measured temperatures
about 150 shakes (at about 8.8 complete shakes per second) was around the point where we
started getting very good, measurable results with Coke cans, so went with that for the
number of shakes.
Because temperature is a big factor in how much foam is produced, the device also reports
the temperature after each run, along with the number of shakes and the time it took
for the run to complete.
Now to the experiment.
There are a variety of ways we could have done this, but as we're far more interested
in the amount of foam coming out, rather than the amount of carbon dioxide, we're choosing
to measure the liquid that comes out of a can, glass bottle, and plastic bottle when
the respective containers are: shaken and then tapped on the side, shaken and then tapped
on the top, shaken but not tapped- simply waiting the same time interval as if we tapped
it, and then shaken, and quickly opened upon removal from the machine.
This latter one is particularly of interest as one alternate hypothesis often put forth
on why tapping the can does increase your odds of avoiding a fizzy bath has nothing
to do with the tapping itself, but is because people tapping the container wait a short
interval before opening it, giving some of the carbon dioxide time to re-dissolve into
the liquid and any formed bubbles to rise to the top where they won't push any liquid
out.
Also, just because we were curious, we ran an additional experiment shaking several cans
and then opening them at intervals to see how long it would take for no more liquid
to be pushed out.
Obviously the results here will vary for other shaking scenarios based on a variety of factors,
but we were really just curious at about broad ballpark numbers here.
So what were our results?
Well, it turns out that the actual tapping of the can does nothing.
However, we were very surprised to note that the seemingly insignificant time interval
here of 20 seconds from shaking to open actually did make a huge difference in the amount of
foam produced.
And, in fact, on the runs when we opened the can as fast as possible after being shaken,
even just a change of a few seconds appears to have made a big difference in foam output,
as you'll see from the results which show that that portion, which was the only one
not precisely timed, is the only place we really saw a large variance in resulting foam,
even though every open in that case was within a few seconds of each other.
As for the rest of the subtle variance in other runs, it was interesting to observe
how even the tiniest change in the opening speed of the containers, which results in
the pressure being released at different rates, made a very measurable difference in the foam
produced to the point where I was eventually able to roughly predict the foam output based
on how I judged my opening speed, despite the fact that in all cases with the can and
glass bottles, it only took a fraction of a second to open them completely.
Specifically, using video footage of a dozen openings on each, we measured an average of
0.07 seconds to fully open the glass bottles and 0.22 seconds for the cans.
With the plastic bottles, this was likewise very similarly timed each time, though took
on average about 1.91 seconds to fully twist the cap off, with the slightly wider variance
there resulting in a bit larger range in output foam.
As for tapping in the air vs. on a hard surface, it would seem this did not have a noticeable
effect either way.
And because it actually takes quite a bit of shaking to get a measurable amount of foam
spillage (using a gram as the smallest increment- for reference here the containers in question
contained roughly 340 grams of liquid), we're guessing in real world scenarios where people
are trying to reduce foam by tapping, nobody's tapping the can vigorously enough to make
a noticeable difference in foam output.
It's also noteworthy that whether tapping 30 times or 50 made no real difference here
in terms of the expected outcome.
Another interesting point is that the plastic bottles produced significantly more foam,
despite it taking much longer to fully open them.
As previously mentioned, based on our observations with all container types, even a fraction
of a second change in opening speed made a noticeable difference in foam output.
And given it took roughly 13 times longer to open the plastic containers fully compared
to the average of the glass and cans, one might have initially expected the plastic
containers would produce much less foam as a result, not more.
Given how much carbon dioxide is added significantly affects the taste of the beverage, we're presuming
Coca-Cola does not vary the initial carbonation level added based on container type.
If that's correct, we're guessing that the plastic containers must contain a much greater
number of nucleation sites than glass or aluminum, ultimately producing many more bubbles for
the same shakes.
This brings us to how long we had to wait until no foam was produced.
We initially expected we'd have to go out to intervals of maybe even as much as an hour
to see the foam completely disappear, but we were woefully incorrect on this point.
In fact, our first experimental run of just 60 seconds of waiting ended up producing no
foam whatsoever despite the 150 vigorous shakes and the small geyser produced at a few second
interval given those shakes.
We then broke it down to 10 second intervals and found at the colder temperature it took
just 50 seconds for foaming out of the container to no longer occur and at 40 seconds, while
there was a slight overflow onto the lid area, it was not even a gram's worth and certainly
didn't naturally spill off the container.
At the higher room temperature, the results were surprisingly similar at 40 seconds producing
just slightly more foam than at the 40 second mark in the colder temperature, measuring
in at 1 gram, 0 grams, and 3 grams in our three runs.
Similarly, the 50 and 60 second marks at room temperature mimicked the 40 and 50 second
marks respectively at the near refrigeration temperature.
As to why there is so little foam being produced after such a short interval, it would seem
to us there are two possibilities, both of which may be coming into play.
The first possibility is that the carbon dioxide is rapidly being redissolved in the liquid.
But as we didn't measure the actual escaped C02 compared to an unshaken container, we
can't say for certain to what extent that is happening.
The second possibility is simply that all the bubbles created from the shaking rise
to the top in this time span and, with no further shaking causing more bubbles to form
at the nucleation sites, the undissolved carbon dioxide is simply escaping when you open the
can without pushing out any liquid.
Supporting the idea that this is the bigger factor in this case is footage of the shaken
glass and plastic bottles which show a dramatic drop-off in created bobbles in a relatively
short time span after shaking is stopped, with those created all rising to the top relatively
quickly and no visible bubbles clinging to the sides as is often stated happens when
people talk about the benefits of tapping the container.
Further, while we didn't measure the carbon dioxide output, for what it's worth, observationally
even when no significant foam was produced, there still sounded like a lot more gas escaping
when opening these shaken cans compared to opening cans that had just been sitting around,
which we did several times just to compare the sound back to back.
Though, of course, further experimentation measuring the actual carbon dioxide output
would need to be done to know for sure.
So there you have it.
We now know for certain that tapping a can of soda does absolutely nothing to reduce
foam and it is actually the short time interval taken to tap the can that is reducing foaming
vs. simply opening the can immediately.
It also very much appears that tapping the container vigorously, which while potentially
could have produced more foam via further agitation, did not produce any practical increase
in fizz.
And while your results will vary based on things like temperature, atmospheric pressure,
and how much a given can was shaken, it would very much appear in all cases you really don't
need to wait more than around a minute or so for things to stabilize to the point where
you can safely open the soda container without risk of a foam over, even if you open the
container quickly.
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Bonus Fact: • Just for fun, we also ran this experiment
on cans of Dr. Pepper to see if the results changed at all.
They did not in terms of the main points already made.
However, what was interesting to note was that the Dr. Pepper produced about half as
much foam on average as the Coca-Cola for each of the scenarios.
There are a variety of potential ingredients that can cause a difference here.
For instance, with many diet sodas that contain aspartame, they end up producing more foam
because aspartame lowers the surface tension of the liquid much more than sugar or corn
syrup will.
It's possible Coca-Cola simply contains more surfactants than Dr. Pepper.
Or it's possible Dr. Pepper just contains much less carbon dioxide than Coca-Cola; given
the amount of carbon dioxide dissolved in the beverage greatly influences the taste
and mouth feel, we're presuming there is a reasonable variance from flavor to flavor.
And, anecdotally, it does always seem like Dr. Pepper goes flat much faster than a lot
of soft drinks....
But that's an experiment for another day.
For now, whatever is the underlying cause, we thought it was interesting to note how
much less foam an equally shaken can of Dr. Pepper produces compared to a can of Coke.
So thanks for watching this video, I know this was a little different than our normal
stuff, but I hope you enjoyed it anyway.
And if you did, please do give it a like below and share it with anyone you think might find
it interesting.
We’d also like to again thank ifixit for sponsoring this one as well as our patrons
on patreon.
As you might imagine, rather than the normal 24 or so hours most of our videos take to
produce, give or take a few hours on average, this one took a lot longer, ringing in at
just over 100 hours; so given the expected YouTube ad revenue on a video like this is
woefully small given our average expected views, without the support of ifixit and our
patrons, we really wouldn’t have been able to spend the time and money to research the
answer on a question like this where the answer isn’t definitively known somewhere.
So thanks again to ifixit and you patrons, and thank you for watching.