Summer break is here! That means it’s time to bring the classroom home and keep young minds active for the next few months. Here’s a quick scientific activity to spark curiosity and discussion in your own kitchen. This is a good one for kids around fifth or sixth grade, though it could even be adapted for those a little older.

Bread mold.

Yeah, it’s gross. But it’s also really interesting stuff. We don’t like to think about it, but mold spores and airborne yeasts are everywhere, drifting around us and looking for a nice, comfortable place to grow. They like to grow on absolutely everything, but what we think of them on most is bread.

For this experiment, we’re testing the hypothesis that mold grows faster in warmer temperatures.

Take 9 slices of any kind of bread, so long as they’re fairly uniform. (Remember to write down the brand and best-by date – this is science; we write everything down). Press your hand flat on each slice of bread, all nine in a row. Then put each one in a zip-lock back and seal them up. Label three “A,” three “B,” and three “C” with a sharpie. Then put the A bags in the freezer, the B bags in the refrigerator, and the C bags in a cupboard that will stay at room temperature or warmer.

Make yourself a counting grid: take one bag the same size as the ones you put your bread in and draw a grid on it, with lines 1cm apart, using a ruler.

Every day, ideally at the same time each day, use your grid to count how many square centimeters have mold on them, and make a chart. Don’t open any of the bags. If you want to be extra thorough, you can take daily photos to see how the mold is growing.

Keep checking for at least ten days. You should really see some growth! Which set has grown most?

With older kids, this can be expanded by trying to identify what is growing. There are plenty of resources online to compare color, texture, and other details. Can you find penicillium? Do you know how that particular mold changed the world?