Why Foods Spoil - Molds, Yeasts, Bacteria (1957)

[Music] a long long time ago people spent much time in search of food when a hunter killed a large animal there was usually more than enough to eat so the family ate and ate heartily they knew that what they could not eat would soon spoil and go to waste the Hunter's wife must have wished she knew how to keep all this food from spoiling but there were only a few ways to keep food from going bad in those days American pioneers of course knew how to preserve some foods and they learned from the Indians how to keep others sometimes new ways of keeping Foods were found accidentally the news of this would spread from neighbor to neighbor for instance people discovered that foods keep longer in cool places so they stored food in suers underground that would stay cool even in the summer but only recently have we we discovered why food spoil now we can buy food weeks or even months before we will actually eat it food can be sent across the country and kept in grocery stores and supermarkets for a long time with no fear of the food spoiling today we know that keeping food fit to eat means keeping three different different kinds of tiny plants out of the food these tiny plants are called moles yeast and bacteria remember the words moles yeast and bacteria first let's learn about moles by watching some food spoil a slice of bread for instance the slice of bread should be moist tiny mold seeds floating in the air will fall on the bread then the bread should be placed in a dark warm place for about 2 days do you see the fuzz that has grown on the bread it is called bread mold moldy bread doesn't taste good let's look at this bread mold through a magnifying glass mold is a tiny plant that fuzz on the bread is a small garden of mold plants and the bread itself is the garden plot the mold seeds were planted when they fell on the bread from the air notice that the bread mold has many little branches and Roots we can see that the roots of the mold grow deep into the bread just as roots of plants grow deep into the soil do you see the dark cluster at the top of the mold plant on the left with a stronger lens we can see that this round dark cluster is a Sac full of mold seeds we call these seeds spores spores are so light that they float in the air and so they can easily get into our food if you take a brush and brush away the mold on bread you will see dust rise this dust is made up of the thousands of tiny spores that have grown on a single slice of bread most molds spoil food but some molds can be put to work for us certain molds give cheese a special flavor and so some kinds of cheese we have we owe to the different kinds of molds but when molds grow on the wrong Foods they spoil the taste and may destroy some of the food value with a microscope scientists study different kinds of mold and separate those that are useful from those that are not different molds have different colors and shapes there are many kinds of molds just as there are many varieties of plants and flowers in a garden each mold acts on a different kind of food in a different way it is usually easy to discover food that has become moldy because the mold plants grow on the surface where we can see them but some tiny plants that spoil food are almost invisible this orange juice for example is being spoiled by another kind of tiny plant called yeast see these bubbles coming up through the orange pulp in the bottom of the glass they tell us that yeast plants are growing in the food yeasts are too small to be seen even with an ordinary magnifying glass but we can see them through a microscope these bubbles are a gas carbon dioxide which yeasts give off when they feed on sugar and water as the yeasts grow and multiply they make the juice turn sour like molds some yeasts are very useful for instance some yeasts make bread dough rise mother deliberately puts a special kind of yeast in the flour she uses to to bake bread as this yeast grows it too will give off carbon dioxide and this gas is what makes bread dough rise now we can see the air holes in the bread which have been made by the gas escaping from the yeast so it is yeasts which make bread fluffy and Light the third kind of plant that spoils food is called bacteria bacteria are the smallest of all plants they can be seen only with the aid of a strong microscope bacteria can be divided into three groups these pictures show one bacteria from each group one kind of bacteria is round another kind is shaped like a number of little sticks or rods the Third Kind is formed into little chains one connected with the other it is difficult to imagine how small bacteria are if all the people in the world were turn into bacteria they would hardly cover this half dooll coin when meat and vegetables spoil and are no longer good for us to eat when milk turns sour bacteria are the cause once again just as with moles and yeasts some bacteria are useful but because many bacteria are dangerous to our health scientists study them an easy way to grow bacteria is to press your fingers on this special jelly there are sure to be bacteria on your fingers Now cover the dish put it in a warm dark place for 2 days see where the fingers touch the jelly millions of bacteria are growing there they grow in a similar way on food and may make it poisonous there are bacteria almost everywhere we should wash our hands often with soap and water to get rid of as many bacteria as possible otherwise some of the harmful ones may be carried into our body and cause disease we have seen that three kinds of tiny plants May grow on foods and spoil them mold s yeasts and bacteria let's learn how to keep these tiny plants from spoiling food one of the oldest ways of preserving food is drying it long ago people noticed that some foods keep longer when dried in the sun fishermen in many parts of the world dry fish in the Sun the drier the fish the longer it will keep some fish are dried and salted the salt helps take the water out of the fish and keep it dry many kinds of meat keep longer when preserved with smoke let's explain why drying foods helps preserve them to do this we'll try an experiment here are some pea seeds the one on the left has been planted on dry soil the one on the right has been watered the seed in the container with the moist soil is doing well but the seed in the dry soil isn't growing at all this experiment shows that a plant even a tiny plant that spoils food needs water to grow one more experiment these are two healthy young pea plants we'll cool the plant on the right and heat the plant on the left see how the plant on the left begins to wilt after the heat is turned on and the cooled plant stops growing we all know that plants don't grow in cold winter weather molds yeasts and bacteria are plants too here are the clues to two more ways of preserving Foods by heat and by cold food keeps in refrigerators because tiny plants either do not grow or grow so slowly that that it will take a long time before the food spoils very low temperatures like those in a freezer kill some of the tiny plants and slow down the growth of others it would take months possibly years to spoil food kept in a deep freeze of your home or in store freezers a lot of foods are preserved by killing moles yeasts and bacteria with heat canning is one of the best ways to keep food from spoiling the food is placed in jars or cans and cooked then it is sealed so that new moles yeasts and bacteria cannot enter the heat kills the tiny plants that would make the food spoil in this way food will keep for many months without spoiling today many people work in plants which preserve food by heating drying and freezing almost all the milk we drink is is quickly heated to a temperature which kills any dangerous bacteria in the milk we call this pasteurized milk the people who pasteurize milk must be very careful to keep the milk at exactly the right temperature many of the foods we eat today are cooked and sealed tightly in cans at large canaries such as this one food in cans will keep almost indefinitely quick freezing is one of the newer ways of keeping Foods meat fruit vegetables even baked and cooked Foods stay fit to eat for a long time when kept in a deep freeze at very low temperatures this jar contains eggs in this machine eggs are dried so thoroughly that they turn into powder as long as they are kept dry no tiny plants can grow in them many foods can be dried into powder form here special light rays are used to destroy the plants that spoil food in this film we have seen that molds yeasts and bacteria are plants that cause food to spoil we have learned that these plants need food moisture and air to live we have learned how to dry Foods so that these tiny plants cannot grow in them we have seen that low temperatures will kill most tiny plants we have also discovered how to destroy moles yeasts and bacteria by heating Foods these are some of the ways to preserve Foods there are many others we will have more and better food as scientists find new ways to keep foods from spoiling oh h