Trial One: non blinded taste test
Sipping from the two cans straight from the refrigerator I found the tastes very similar and hard to distinguish. "Maybe Pepsi tastes a little better?" I noted. "Both mainly taste sweet. There's a lemony sourness in the background."
"Coke seems to have a bit more of the sour flavor. I want to say Pepsi tastes 'smoother' or is 'more balanced' but I'm not sure what I mean by those words."
"If these were the same cola but someone told me they added a little grapefruit juice to one I would think it was the Coke."
In Blink, Malcolm Gladwell recounts the drama of the Pepsi Challenge, a pivotal moment in the Cola Wars (my favorite war).
In the early 1980s, the Coca-Cola Company was profoundly nervous about its future. Once, Coke had been far and away the dominant soft drink in the world. But Pepsi had been steadily chipping away at Coke's lead. In 1972, 18 percent of soft drink users said they drank Coke exclusively, compared with 4 percent who called themselves exclusive Pepsi drinkers. By the early 1980s, Coke had dropped to 12 percent and Pepsi had risen to 11 percent and this despite the fact that Coke was much more widely available than Pepsi and spending at least $100 million more on advertising per year.
In the midst of this upheaval, Pepsi began running television commercials around the country, pitting Coke head-to-head with Pepsi in what they called the Pepsi Challenge. Dedicated Coke drinkers were asked to take a sip from two glasses, one marked Q and one marked M. Which did they prefer? Invariably, they would say M, and, lo and behold, M would be revealed as Pepsi. Coke's initial reaction to the Pepsi Challenge was to dispute its findings. But when they privately conducted blind head-to-head taste tests of their own, they found the same thing: when asked to choose between Coke and Pepsi, the majority of tasters 57 percent - preferred Pepsi. A 57 to 43 percent edge is a lot, particularly in a world where millions of dollars hang on a tenth of a percentage point, and it is not hard to imagine how devastating this news was to Coca-Cola management. The Coca-Cola mystique had always been based on its famous secret formula, unchanged since the earliest days of the company. But here was seemingly incontrovertible evidence that time had passed Coke by.
Coca-Cola responded to the challenge with the disastrous New Coke formula, which performed better in blind taste tests.
As Gladwell explains, the problem is that when people have just a sip of a drink in a taste test, they prefer a sweeter hit, something to amuse the bouche. But when they buy a case of soda to drink at home, they might prefer a flavor with less sweetness, more "balanced."
The two colas have very similar ingredients.
POTASSIUM BENZOATE (TO PROTECT TASTE)
POTASSIUM BENZOATE (PRESERVES FRESHNESS)
The brands have experimented with a number of ways to add vim without adding calories and now use aspartame in the U.S. market.
I noticed that my 7.5 fluid ounce (222 mL) can of Diet Pepsi had 22 mg of caffeine; the same size can of Diet Coke had 28 mg. I have little doubt that the drug affects the appeal. I remember being in a restaurant once and noticing that I felt happy, not absurdly happy but somewhat unaccountably happy, and realized I had had a few refills of Diet Coke and was probably cheered up by the drug. Caffeine probably wouldn't affect a quick taste test but might provide positive associations over time.
Pepsi One has the highest caffeine content of any cola, lab tested 57 mg per 12-ounce can. Diet Coke has 46 mg, regular Pepsi 39 mg, Diet Pepsi 37 mg, and regular Coca-Cola 34 mg.
Trial Two: blinded taste test
After struggling to distinguish the two colas when I knew what they were, I knew it would be a challenge drinking from the wrapped cans. After a few sips I thought the can on the Right was "more grapefruity?" I sensed that there was no way I could ever identify one unknown drink by itself, any difference between the two was faint. After a lot of sipping I decided that the Right can was Coke, with confidence of 75% (barely better than a 50% guess).
After a while the drinks were not as cold and maybe less fizzy and the Right can started tasting better, the Left can seemed to have more of the sour flavor. I changed my guess to Left = Coke with 60% confidence, which happened to be correct.
I conclude that, for me, the two diet colas are completely interchangeable.