Agar plate culture lets you grow germs evenly across a jelly-filled dish so you can see what stops them. This project streaks E. coli onto agar dishes and then exposes each one to a different spice to watch which ones block growth. Because the jelly food feeds the bacteria across the whole surface, any gap in growth shows where a spice killed the germs.

Some foods can stop germs from growing without even touching them. In this experiment, a quarter teaspoon of spice sits on the lid of an upside-down agar dish, and its vapors drift down onto E. coli bacteria below. When coriander vapor alone was enough to block every bacterial colony, it showed that a natural food's germ-stopping power can travel through the air.

One food safety step is choosing ingredients that naturally fight germs. This experiment tests whether common spices can kill food-spoilage microorganisms. Coriander stopped all bacterial growth on the agar dishes — showing that what you add to food can matter as much as how you store it.

E. coli is a common bacterium that scientists use to test whether substances can stop germs from growing. In this experiment, you streak E. coli across agar dishes and expose it to spice vapors. Some spices block all bacterial growth, showing how this gut bacterium responds differently to different compounds.