Floaters: How Does a Penicillium Mold Grow and What Does it Look Like?

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Author: Janice VanCleave


How does a penicillium mold grow and what does it look like?


  • baby-food jar
  • dishwashing liquid
  • warm tap water
  • apple cider
  • magnifying lens


WARNING: After performing the experiment, discard all molds and the foods on which they are grown. SKIP THIS EXPERIMENT IF YOU ARE ALLERGIC TO MOLD.

  1. Wash the jar with warm, soapy water and rinse with warm tap water.
  2. Fill the jar with apple cider.
  3. Place the open jar of apple cider in a warm, dark place.
  4. Use the magnifying lens to study the surface of the apple cider in the jar; make daily observations of the surface of the cider for two weeks.


After a few days the surface of the cider appears to have round, fuzzy blue-green floating pads on it. These circles resemble floating lily pads. In time, the growths cover the entire surface of the liquid.



The powdery growth on the surface of the apple cider is the mold penicillium. The time it takes for penicillium mold to grow depends on the temperature of the room. In a warm room, signs of growth may appear in two to three days. This blue-green mold is one of the most common and widespread of all fungi. The base of the floating penicillium pad is made up of threads called hyphae. This tangled mass of hyphae is called a mycelium. At the top of each hypha thread are blue green spores. The large number of spores gives penicillium its bluish-green color and fuzzy appearance. Besides its medicinal purposes, penicillium is used to make cheeses such as Roquefort. This cheese is blue because of the large numbers of spores present.



Try It With A Microscope

Microscope Procedure

  1. Collect a sample of the mold by gently brushing an art brush across the surface of the mold.
  2. Tap the brush on a clean microscope slide.
  3. Observe the slide under low power.
  4. Adjust the mirror below the slide to produce as much illumination as possible.
  5. Move the slide around to view different areas.

Microscope Results

Dark clumps and specks as well as threadlike structures are seen across the viewing field.

Let's Explore

  1. Would the penicillium mold grow in a closed jar? Repeat the original experiment, placing a lid on the jar.
  2. Does the type of fruit juice affect the results? Repeat the original experiment using other fruit juices such as cranberry, grape, and cherry.

Show Time!

    1. Will mold grow on solid foods? Place a slice of bread in a sealable plastic bag. Add ten drops of water to the inside of the bag. Seal the bag and place it in a dark, warm place for ten days. Use a magnifying lens to observe the surface of the bread daily for signs of mold. Make colored diagrams of your observations.
    2. At the end of ten days, ask an adult to cut a thin slice from the bread piece. Place the slice on a microscope slide. Slowly move the slide around as you observe it under low power, with the slide brightly lit from above by a desk lamp. Make a colored diagram, and display with diagrams of the bread mold observed with the magnifying lens.

Check It Out!

The penicillium mold is used to make the antibiotic called penicillin. Find out more about the penicillium mold. What is an antibiotic? How did the British scientist Sir Alexander Fleming discover that penicillium mold had antibiotic properties?

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