What Is the Difference Between Right Twix and Left Twix? Ask Paul

Rigorous scientific testing finally answers the question.

Published July 20, 2022.

Terry asked: Is there an actual difference between the two Twix bars in a single package?

Twix, for those who aren’t familiar with it, is a candy bar consisting of a crumbly cookie that’s topped with caramel and enrobed in milk chocolate. It’s traditionally sold in packs of two slender bars.

About 10 years ago, the makers started a clever advertising campaign, urging customers to form an opinion about which of the two bars in a Twix package—labeled Right and Left—they preferred. But aren’t they the same, everyone wondered?

Twix marketing responded with amusing obfuscation. Right Twix, they say, “features chewy caramel on crisp cookie, cloaked in velvety chocolate” whereas the left bar is “smooth caramel on crunchy cookie, enveloped in creamy chocolate.”

In 2017, they even started selling 2-packs of Twix labeled as containing “Two Left” or “Two Right” Twixes.

Are they really different? It seems unlikely, but not impossible.

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A Scientific Test

Science has a simple way of finding an answer to this sort of question: sensory discrimination testing. It’s a formalized way of evaluating whether tasters can actually tell the difference between two foods.

One of the most well-known discrimination tests is the triangle test. In this setup, each taster is given three identical-looking samples, and told that two of them are the same, and one is different (which is the truth). The tasters (as many as possible, but usually at least 30) are asked to taste each sample in order and indicate on a form which one they think is the odd sample out. If they have no idea, they must give their best guess.

When the results are tabulated, we count how many of the tasters correctly identified the odd sample. If about half of the tasters got it right, the implication is that there’s no discernible difference between the two products. But if far more than half the tasters identified the odd sample, the two products are shown to be different.he more correct answers, the more significant the result.

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I set up a simple test. I bought 12 Twix bars from a variety of retailers, half in packages marked “Left” and half in ones marked “Right.” I opened all the packages, keeping Left and Right separate, removed the ends of each bar for uniformity (and for a snack), cut each into short segments, and divided them all into two containers, Left and Right. Then I rounded up some willing tasters.

Each taster received a plate containing three Twix segments, either two Right and one Left, or two Left and one Right. I ensured they were laid out in a variety of configurations: RLR, LRR, LLR, and so forth. Each Twix segment was labeled with a meaningless numeric code. I asked each taster to write down which of their three was the different one.

Then I tallied the results. If you want to try this test at home and derive your own results, stop reading here, and send me your results.

Are Right Twix and Left Twix Different? What the Science Says

I only found 11 tasters to participate at short notice, which does not provide very robust statistical significance. So it’s not impossible that my results could be explained by coincidence or error. But, of my 11, 5 of them correctly identified the odd sample, and 6 of them failed to identify the odd sample. On that basis I'm comfortable saying: There is no difference.

Paul Adams is America's Test Kitchen's senior science research editor. He's a former restaurant cook, food journalist, and science reporter.

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