The Fascinating World of Fungi
- Wednesday, February 01, 2006
Wait a couple more days until there's a large area of mold on the food. Which set of bread has the most growth on it, the one in the light or the one in the dark? What about the scraps? Do some scraps have more mold than others?
As you discuss what you see, you might also want to write down your observations and make sketches. Use a magnifying glass or a microscope, if you have one, to look at the mold spores close up. What do you see? (To view under a microscope, use a sharp knife to carefully scoop up some of the mold and set it on a microscope slide. Look at the mold under low and then high power.)
For further study, come up with your own experiments that help answer the following questions: Which foods are most susceptible to mold, ones high in starch or high in protein? What difference does the presence of sugars make? If mold grows best in a slightly acidic environment (5-6 pH), how might you make it grow faster? Think about what foods are more acidic; for instance, vinegar and lemon juice are highly acidic at 2-3 pH, while apples have an acidity of 3-4 pH.
How Can You Prevent Mold Growth?
Almost every processed food has some kind of preservative in it, to keep it from spoiling. White bread usually has far more preservatives than regular wheat bread. Fruit and vegetables are harder to preserve, although often apples are coated in a thin protective wax. Refrigeration often keeps food preserved for at least several days, because the cold temperature inhibits mold and bacteria growth.
Use the peelings from 2-3 apples, pears, or oranges for this experiment. Put an even amount of peels on four paper plates and set them in a place with some sunlight. Now sprinkle about a teaspoon of salt over the peels on one plate, and label the plate "salt." Do the same for another set, but this time with sugar. For the last one, choose your own "preservative"--it might be from the spice rack or it could be a mild household cleaner from under the sink! Which set of treated peels do you expect to be most resistant to mold growth? Which do expect to have the most growing on it?
Observe mold growth on each after 2-3 days. Look again each day after that for the rest of the week. How does the mold compare on each? Was it how you predicted it would be?
Have you ever made bread? For non-sweet breads, usually you have to mix active dry yeast with water and then mix it with dough and let it rise. The yeast breaks down sugar molecules in the dough and converts it to carbon dioxide (CO²) gas, alcohol (which evaporates as the bread cooks), and water. The CO² is what causes the bread dough to rise. Look at a piece of bread, homemade or store-bought. Do you see the "holes" in it? These are caused by bubbles of CO² from the yeast.
What difference does temperature make to yeast growth? Test this by adding a teaspoon of active dry yeast to a cup of cold water and a teaspoon to a cup of warm (but not boiling) water. Observe them both. How does the yeast act in each? Use your eyes and your nose! In the warm water, the yeast turns slightly foamy almost instantly and gives off a strong "fermenting" smell. As they begin to reproduce, the round yeast cells begin to dissolve in 1-2 minutes and form a thick, sticky coating on the water. Stir the yeast into the water and see what happens. It will form globs of yeast that stick to the spoon. Now compare the yeast in the cold water. In the same amount of time, it will also form a coating on the water's surface, but without looking dissolved. You'll still see lots of dry yeast on top, and when you stir the water, the yeast is not so sticky. In the beginning, there's also less of a smell, as the spores take longer to begin fermenting. >From this, you might conclude (correctly) that yeast is most active in a warm environment!
Don't Forget Mushrooms
Although you probably won't be able to see them on store-bought ones, mushrooms have long root-like hairs called mycelium that take care of digestion and absorption. This is actually the main part of the mushroom! The part we're used to seeing, a stem or stalk with a cap on the top, only grows at a certain part of the mushroom's development. These parts are still important, though! They form the "fruiting body" that grows out of the mycelium and release spores, so that the mushroom can reproduce. Underneath the cap are gills, which hold the spores.
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