Why Does a Sandwich Taste Better When Someone Else Makes It?

You are standing in your own kitchen. You used your own bread, your own cheese, your own tomato and lettuce, and you toasted the whole thing carefully. Then somebody else stands in the same kitchen, uses the same ingredients in the same order, cuts it in half and holds out the plate, and the sandwich is unmistakably, irritatingly better. Nothing in the ingredients accounts for it. So where is the difference being kept?

The explanation most often offered online points to a study from Carnegie Mellon University. According to the university’s news release, published on ScienceDaily in December 2010, the researchers Carey Morewedge, Young Eun Huh and Joachim Vosgerau asked people to imagine eating sweets. Participants who imagined eating 30 chocolate sweets went on to eat significantly fewer of them than people who imagined eating only three, or who did a different task. A follow-up experiment with cubes of cheese found the same pattern.

The researchers explained the result through habituation. “Habituation is one of the fundamental processes that determine how much we consume,” Vosgerau said in the release. The study, published in the journal Science, overturned the long-held assumption that thinking about a desirable food simply makes you want it more. Repeatedly imagining eating something, it suggested, can wear down your appetite for it in much the same way that actually eating it does.

It is important to be clear about what the study did not do. It did not involve sandwiches, kitchens or anybody making lunch for anybody else. Applying it to a homemade sandwich is a guess, though a reasonable one: the person making the sandwich spends several minutes looking at it, handling it and thinking about eating it. A related idea has a longer history. In a classic 1981 study, Barbara Rolls and her colleagues found that once people had eaten a food, its pleasantness fell more than that of foods they had not eaten, which is why a new flavour can revive an appetite that seemed finished. They called it sensory-specific satiety. It was first described in 1956 by the French physiologist Jacques Le Magnen, and the term was coined in 1981 by Barbara J. Rolls and Edmund T. Rolls.

There is also the matter of surprise. When you make a sandwich yourself, you know exactly where the thick bit of butter went and which corner got all the cheese. A sandwich somebody else made still has a first bite you cannot predict. No study measured that part, but anyone who has eaten a sandwich cut into triangles by another person will recognise it.

The rest of the answer probably cannot be weighed on anything. A sandwich made for you is a small piece of evidence that someone spent a few minutes thinking about your lunch, and that thought appears to be edible. It also explains the saddest sandwich in the world, which is the one you made for somebody who then left the house, and which you now have to eat yourself.