No matter which type or brand of chocolate bar you prefer to indulge in, there is one thing that all of them have in common: the bar is divided into smaller segments by grooves running through it. The segments are more commonly in the shapes of squares or rectangles, but no matter the shape, the grooves are present in every one of them. Here is why that is.
The grooves are a point of weakness that has been engineered into the slab of chocolate. And for good reason. As Czerski shared in an article on The Wall Street Journal in 2024, “Chocolate is a very sophisticated mixture made mainly of cocoa solids, cocoa butter, sugar and (often) milk.
Because it’s solid at room temperature but melts in your mouth, and that’s because cocoa butter has a melting point of 93-100° Fahrenheit, just right to make both possible.”, it’s clever.
The grooves in chocolate bars are more important than the shapes that they divide the entire bar into from a mechanical point of view, according to physicist Helen Czerski.
“We need chocolate to be solid under most circumstances, so we can transport it with minimum mess. But breaking a flat, solid slab into pieces can be a very haphazard process. Bending the slab takes a lot of force, and hidden irregularities—perhaps an air bubble or a nut—will cause it to break in unpredictable places. So chocolate makers have put the flaws in plain sight by giving the bars grooves. If a person has to break a big unwrapped bar of chocolate in half, they are likely to turn it so the grooves are facing away from them, use their fingers to pull the ends of the bar towards themselves and their thumbs to push the middle away. “But the grooves aren’t just thinner parts of the bar—they’re U-shaped or V-shaped, and when the top of the U or V is stretched outward, all the stress is concentrated at the bottom of the valley. The sharper the indent (the more V-shaped) it is, the higher the stress concentration is at the point. So the chocolate bar will break at the bottom of the valley, and the person does not have to put a huge amount of effort into making it happen. The V-shape is an engineered weakness, put there both to make it easier to break the bar and to control where it happens. The smaller squares or rectangles in a bar of chocolate make portion control easier by giving visual cues. Each cube feels like a natural stopping point, and one is not dependent on hunger alone to decide how much to eat in one go. Moreover, breaking the chocolate bar effortlessly into smaller, equal segments makes sharing much easier. Each square becomes one serving, and equal distribution becomes simple math.
“As you do this, the bar bends outward, stretching the side facing away and squashing the side closest to you,” explained Czerski.
