And the award for the world's most paranoid dieter goes to...

January 5, 2006 8:33 PM

Are there any simple tests that can be done (besides tasting) to determine if a given sample is diet coke or regular coke?

Without using taste or smell, is there a simple way to distinguish between coke and diet coke?

One possible way to distinguish: test strips that react differently to the sweeteners in each one? There are strips you can buy that will tell you if you have ketones in your urine, if a substance is an acid or a base, etc etc. Maybe something similar would work? Maybe the PH is significantly different and PH test strips could be used?

posted by skjønn to Science & Nature (33 answers total)

I remember seeing in chemistry class that if you a can of diet soda and a regular soda in a tub of water, one of them sinks -- can't remember which one. Thus, the specific gravity must be different, and if you have a known volume, you could weigh them.
posted by cameldrv at 8:47 PM on January 5, 2006

Well, the sweetener in Diet Coke is aspartame, which is a phenalalanine/leucine amino acid dimer. Brief googling hasn't led me to test strips for aspartame. I'm guessing you might want to try searching for diagnostic strips used to keep phenylketonuric (sp?) babies healthy. These are kids that can't metabolize phenylalanene, and so can't have the sweetener used in Diet Coke.
posted by killdevil at 8:53 PM on January 5, 2006

Response by poster: Thanks cameldrv: I think this is it: http://www.middleschoolscience.com/dietcoke.htm

The only thing is, I'm working with samples that are not in cans.
posted by skjønn at 8:53 PM on January 5, 2006

Response by poster: killdevil, do you know that these test strips exist or do you just think they might exist? Thanks to the both of you btw.
posted by skjønn at 8:55 PM on January 5, 2006

Actually, researching a bit further, aspartame is the two amino acids phenylalanene and aspartic acid. See here. I feel sure that there's an easy test for parents of phenylketonuric children, though I don't know for certain.
posted by killdevil at 9:03 PM on January 5, 2006

This 6th grader used a refractometer to measure the sugar content in various liquids (including Coke). Seems like that would work for you..
posted by smackfu at 9:12 PM on January 5, 2006

trying pouring some into a glass. diet coke fizzes much more.
posted by dawdle at 9:15 PM on January 5, 2006

Response by poster: For reference:

Coca-Cola (Classic)
Carbonated water, high fructose corn syrup and/or sucrose, caramel color, phosphoric acid, natural flavors, caffeine.

Diet Coke
Carbonated water, caramel color, aspartame, phophoric acid, potassium benzoate (to protect taste), natural flavors, citric acid, caffeine.
posted by skjønn at 9:17 PM on January 5, 2006

Response by poster: pH of various sodas
Ok it looks like the pH test strips may be the way to go. Can anyone recommend a pH test strip that will be good enough to distinguish between a pH of 2.63 and 3.39 reliably? I want to carry these around in my purse.
posted by skjønn at 9:25 PM on January 5, 2006

I'm completely curious about the reason behind this experiment in identification. Please tell us?
posted by chiababe at 9:27 PM on January 5, 2006

If it's a case of different specific gravity, a wine maker's hydrometer would probably provide an answer. Much cheaper than a refractometer, and available at a wine making store for about $7.
posted by slogger at 9:29 PM on January 5, 2006

isn't diet coke "blacker" than regular? i've heard waitress persons say this when trying to remember which drink goes where.
posted by muddylemon at 9:33 PM on January 5, 2006

Benedict's solution tests for the aldehyde group in simple sugars and should turn red from the fructose in the regular coke. I don't think regular chem lab pH strips will give you distinguishable results.
posted by zadermatermorts at 9:33 PM on January 5, 2006

Best answer: My first guess would be glucose test strips. This person claims to have tried them and found they didn't work with every type of sugar used to sweeten drinks, however. But that's some random guy on the internet, so who knows. I'd probably buy some strips if they're cheap and at least give it a shot.
posted by mragreeable at 9:35 PM on January 5, 2006

Response by poster: chiababe: I'm on a weight loss diet. I drink diet soda (yes it helps me and no I don't want to get into a discussion on why diet soda is bad).

Recently my weight loss has been stalled. I've been sticking to my plan pretty well so I was mystified until today...

My little sister took a drink of a diet coke I had bought from the Mobil food mart. They sell a 32 ounce fountain drink for 69 cents. "This isn't diet!" she protested.

So we went and got some regular and diet coke and taste tested it with the sample in question. Indeed, it wasn't diet.

I've been drinking at least 64 ounces of non diet soda a day with god knows how many calories for a week now. No wonder my weight loss has stalled.

Anyway, call me crazy, but I am so determined never to let this happen to me again.
posted by skjønn at 9:37 PM on January 5, 2006

To be honest, I'm completely baffled that anyone could drink even a single mouthful of regular coke and not realize that it's not diet. Even coke zero, which tastes more like regular coke than it does like diet coke has a noticeable chemical aftertaste to it.

You can also tell, though, just by touching them. Regular coke is far stickier than diet. Dip your finger in regular coke and rub it off and you're left with a sticky finger. Do the same with diet coke and it basically disappears.
posted by jacquilynne at 9:48 PM on January 5, 2006

I'm with 23skidoo - I know that spilled Diet Snapple isn't sticky while normal Snapple is - wouldn't the same be true for Coke?

I've been drinking Pepsi Blue Coke Zero which is zero-calorie but tastes almost like real Coke. Not sure if it's sticky.
posted by nicwolff at 9:54 PM on January 5, 2006

Since you're getting it from a fountain, the pH test might not be reliable. If it's a place that can hook up the wrong soda, I'm sure they can do the mixture wrong. A slightly watery coke would have a higher pH than a properly mixed one.

Idea: Pour a quick blast of diet or normal coke. Taste it. Pour a quick blast of the other. Taste it. If they're different, you're probably safe. If they're the same, then, er, you're probably not and complain. (I'm assuming that if the normal coke was switched to diet coke (and diet to normal), a normal coke drinker would complain on the spot, even if you can't tell the difference, there's a lot of die-hard coke drinkers that can.) I've never been to a place that would care if you do this, but who knows.
posted by skynxnex at 10:00 PM on January 5, 2006

That mobil food mart should be careful. All it would take is one diabetic....
posted by gergtreble at 10:03 PM on January 5, 2006

Response by poster: Awesome!! AskMe to the rescue again :) I'll be purchasing some Diastix tomorrow.
posted by skjønn at 10:13 PM on January 5, 2006

A cheaper/easier solution than buying testing strips and using them every time you buy a soda:

Just buy the soda in a can or bottle, instead of getting the fountain drink.

I drink an obscene amount of diet soda, and I know it's diet because the can says so.
posted by JekPorkins at 10:19 PM on January 5, 2006

Without using taste or smell

I don't know about you guys, but I can clearly see a difference between the two. Diet Coke appears redder/browner to me, with the clearest difference being the color of the bubbles and froth at the surface.
posted by frogan at 10:50 PM on January 5, 2006

Well, for an expensive option, PNNL developed a sound-based technology that could be used on closed containers to determine the contents of that container (the substance had to have been "tested" under known conditions & the size/shape of the container and the temperature had to be known for it to work). This device can distinguish coke from diet coke without opening. However, I think the devices run like 20,000 dollars or something. article at seattle times only mentions the coke vs pepsi bit, but I believe it does diet coke vs regular too. (Link requires registration, but its free so use bugmenot).

Rachael

(Disclosure: I used to work for the company developing it commercially, although not on this device.)
posted by R343L at 11:20 PM on January 5, 2006

i believe that when poured, diet coke has brown bubbles, regular coke has cream colored bubbles.
posted by tumble at 11:41 PM on January 5, 2006

You could use a brix meter/refractometer, too.
posted by milkrate at 12:12 AM on January 6, 2006

if you use both to "write" on paper, then let them dry and hold the paper over a lighter or match, you should detect browning where the classic coke was as the sugar caramelizes. obviously the paper will brown too (you need to be careful, it's also likely to catch fire), but in the case of sugar solution you should see the "writing" go brown; for diet coke you won't.

(this is a guess based on childhood "secret writing" tricks.)
posted by andrew cooke at 3:32 AM on January 6, 2006

also, they taste vey different, at least here in chile
posted by andrew cooke at 3:33 AM on January 6, 2006

Regular coke dries sticky while diet does not. My diabetic grandmother would clean her glasses with diet coke if it was the only thing available at the time.
posted by malp at 5:34 AM on January 6, 2006

I'll be really interested to see what you find out. Please come back and tell us.

I want to suggest another possibility, though: It may be the the taste difference is a result of the drink not being Coke, rather than not being diet. It could be a cheaper diet soda. It's not unheard of. I worked in a restuarant once where the cola was some cheap generic from Sysco. Customers ordered it as "Coke" or "Diet Coke" and we referred to it by those names -- even on the menu. In fact, I worked there for quite some time before I discovered it wasn't really Coke.

I'm a big Diet Coke drinker; I had noticed it tasted odd, but to be honest, I had thought it was simply badly mixed Diet Coke (too much seltzer, not enough syrup). I was surprised to learn they were saving a fraction of a cent per serving by going with a cheaper syrup. It was still Diet, it just wasn't Coke.

The reason I found out? A customer questioned it one day. Actually called me over and said "Are you sure this is Coke?" That spurred a research excursion to the pumps in the basement. Viola! The owners admitted it wasn't Coke. Their defense on the menu angle was that they had switched and just never reprinted the menus, and "most people don't notice". I'm sure people did notice, like me and my customer; it's just that most people didn't mention anything about it, chalking it up to a bad Coke experience.
posted by Miko at 7:23 AM on January 6, 2006

My non scientific method for testing is essentially.... diet fizzes more!
posted by rc55 at 8:36 AM on January 6, 2006

Sugary drinks dry sticky; sugar-free drinks don't.
posted by Doohickie at 10:47 AM on January 6, 2006

Miko: Coke has been known to sue restaurants over that. They freak the fuck out.
posted by klangklangston at 1:57 PM on January 6, 2006

They freak the fuck out

huh -- makes sense. I thought it was pretty low-down myself, and I'm not the world's most-recognized brand with a giant global distribution network. They are one tough company. Anyway, just as a Coke drinker myself, I thought it was really unfair. When you want a Coke, only a Coke will do. Still, I'm sure a lot of restuarants try this and just hope not to get caught.
posted by Miko at 2:18 PM on January 6, 2006