How to Use Gelatin as a Culture Medium for Growing Bacteria

Pick a nutrient to add to your culture. Different bacteria require different types of nutrients to sustain their growth, so the nutrients you'll need depend on what you want to grow. The best way to find out is through trial and error -- if you prepare multiple cultures with different nutrients in each, for example, you might end up with different bacteria in each culture. Pick a source of nutrients similar to what the bacteria you want to grow might encounter in their normal environment. Soil, compost, manure, beef broth and dry vegetation are all good choices.

Fill your saucepan part-way full of water. Add the baby food jars, the mixing jar and the measuring cup, then bring the water to a boil and boil the contents for about 10 minutes. This step ensures your jars are as sterile as possible. Some bacteria can survive boiling, so if an unexpected inhabitant turns up in your culture, you may have inadvertently found one of these highly heat-resistant strains.

Pour some of the boiling water out of your saucepan carefully and without breaking or removing the jars. Using an oven mitt or a pair of tongs, remove the baby food jars and other glassware and place them upside-down on the paper towels to dry. Be aware that hot glassware and boiling water can cause serious burns -- ask an adult for help with this part if you are under the age of 15.

Allow the measuring cup to cool, then use it to add 2 cups of water back to the saucepan. Add a small amount of the nutrient you chose earlier on and bring the mixture to a boil. Boil it for three to five minutes.

Add 1/4 cup of the boiled mixture to the jam jar and sprinkle on a packet of gelatin. Allow it to cool. Meanwhile, heat the remaining mixture in the saucepan back to a boil.

Pour 1/4 cup of the boiling mixture from the saucepan into the jam jar. Gently swirl the jam jar to mix up its contents.

Pour the jam jar's contents into your baby food jars. Recap them and keep them in the refrigerator until you are ready to use them.

Use a clean cotton swab fresh from the package across a surface of your choice to pick up some bacteria. You could, for example, swipe the swab across your bellybutton or use it to pick up a little pond water -- both environments that contain interesting bacteria. If you need to moisten the cotton swab first, do so using boiled water only.

Wipe the swab across the surface of the gelatin in a baby food jar. Do not puncture the surface of the gelatin in the process. Try to spread the microbes out across the surface of the gelatin.

Recap the jar and decide where you want to put it. Different conditions, like heat and light, may favor the growth of different kinds of bacteria. If you cap the jar loosely, you'll allow more oxygen to enter, while a tightly capped jar will limit the amount of oxygen. Experiment with different conditions and see what happens with each.

Wait a few days to see what grows in your jar(s).