To get started, you’ll need to make your agar and fill some petri dishes. Use a clean, microwave-safe container to mix the agar with water and then boil it. A quart-sized bowl works great. These proportions make enough nutrient agar to prepare two petri dishes. Stir these together well:

• ½-teaspoon agar (1 1/5 grams)
• ¼ cup (60 milliliters) of hot water

• Bring the agar mixture to a boil for three minutes to completely dissolve the agar.

CAUTION: Adult supervision is required to boil water. If you are using a microwave oven to boil the mixture, be careful not to let it boil over. The mixture should be clear with no particles floating in it after boiling.

Remove the mixture from the microwave or the stovetop and allow it to cool for three to five minutes before moving on to the next step.

Take the lid off of the petri dish and carefully cover the bottom half of the petri dish with the warm nutrient agar mixture.

Loosely cover the bottom portion and allow the mixture to cool and harden for at least an hour. You can offset the lid so excess moisture can escape.

• NOTE: Just like gelatin, agar needs to boil for a certain amount of time to properly gel. If necessary, pour any unset mixture in each Petri dish back into the bowl and microwave it again until you see it boil. Watch it boil for 10-15 seconds before turning off the microwave, but don’t let it boil over. Make sure there are no floating particles. Pour the hot agar mixture back into the dishes just like before and it should solidify within an hour.

Once the agar is set and cooled, it’s time to collect some bacteria on the end of a cotton swab. Roll a clean cotton swab in your mouth or test something even more gross, like the keys on a computer, a cell phone case, the pump handle of a soap dispenser or the remote control.

• NOTE: You might want to collect a sample from a computer keyboard on half of the Petri dish and leave the other half for the test in Steps 8 and 9. Remember, you must use clean cotton swabs for each sample. In order to get a good sample, lightly dampen the cotton swab with water. Be sure to roll the swab on the surface you’re testing so that it’s completely covered and has picked up as much bacteria as possible. You want to cover the entire cotton end of the swab with invisible bacteria.

Lift the lid off the petri dish and lightly draw a squiggly line in the agar with the end of the cotton swab. Roll the swab in your fingers as you draw the line. Replace the lid and label the dish with the date and the name of the item you tested.

• NOTE: Moisture coming from the agar can be a problem. Many people turn the petri dish over during this time to prevent moisture from dripping onto the growing colonies.

• SUGGESTION: Place no more than a drop of a hand sanitizing gel in the middle of one of the squiggles. The hypothesis is that the antibacterial chemical in hand sanitizer will keep bacteria from growing there.

Use a sanitizing wipe to thoroughly clean one of the surfaces you tested in Step 6.

With a clean swab, redo the squiggle test in the other half of the Petri dish from Step 6 to confirm your cleaning efforts.

Before growing anything, some people place each Petri dish into separate zipper-lock bags. Place the upside down dishes into a warm, dark place to grow. A temperature around 98 degrees Fahrenheit (37 degrees Celsius) is best, like in a closed container on top of a cable box. In a short time, you’ll be greeted by an amazing variety of bacteria, molds and fungi. You likely see more and larger colonies over the next few days. You shouldn’t see too much growth where the hand sanitizer was used — you might even see a halo around each location, which is called the kill zone. Measure and compare the size of the kill zone to determine the effectiveness of different antibacterial agents.

• REMEMBER: Do not open the dishes once things begin to grow. You could be culturing some serious bacteria and not even know it. The comfort is that they were around you all the time anyway and now you can see them. Just be careful.

Bacteria, like what you’re growing, will often stink and make their presence known after a short time. These are not toys or curiosities you’re growing. Proper disposal is essential for both safety and sanitation. Seal all the petri dishes in larger zipper-lock plastic bags. You can add a generous shot of chlorine bleach to the bag before sealing for an extra level of destruction.

• REMEMBER: When you’re done, do not open the bags. After you’ve analyzed the cultures, dispose of the sealed bag containing the petri dishes with bacteria into the trash.

At the end of the growing period, observe the petri dishes and write down, draw or photograph what you see. Turns out, Mom is right — it is super important to wash your hands with soap and warm water whenever you can.