Pour one cup of milk in each jar. Use the lids to seal the jars. Rotate the jars back and forth several times and observe how freely the milk in each jar moves. Repeat step 4 each day for 7 days, or until a change appears in one of the jars. Discard the milk in both jars.
Microbes are microorganisms, which are tiny living things visible only under a microscope.
Bacteria, mold, and yeast are microbes commonly found on food. These 3 types of microbes do have beneficial effects. For example, bacteria are used in making buttermilk, molds are used in making cheeses such as Roquefort, and yeast is used in making bread. Bacteria can make milk sour, yeast can make pickle juice develop a film, and a black mold that looks like a beard can grow on bread. It is not advisable to try to make spoiled food fit for eating by skimming away film or trimming away moldy areas.