Yeast Alive! Watch Yeast Live and Breathe
Bring Science Home: Activity 6
Introduction
Have you ever looked closely at a piece of sandwich bread—really closely? Notice all of those tiny holes? They probably got there thanks to tiny living organisms called yeast. Even though these organisms are too small to see with the naked eye (each granule is a clump of single-celled yeasts), they are indeed alive just like plants, animals, insects and humans. In fact, we have some interesting things in common with these little creatures!
Have you ever looked closely at a piece of sandwich bread—really closely? Notice all of those tiny holes? They probably got there thanks to tiny living organisms called yeast. Even though these organisms are too small to see with the naked eye (each granule is a clump of single-celled yeasts), they are indeed alive just like plants, animals, insects and humans. In fact, we have some interesting things in common with these little creatures!
When you breathe out, part of what you are exhaling is a gas known as carbon dioxide. Yeast also releases carbon dioxide when it is active (although it's way too small and simple an organism to have lungs). Yeast are so small you can't see individual ones very well. So how can you tell if they are alive or not? You can enlist a whole bunch of them to blow up a balloon for you!
Background
When you buy a packet of baker's yeast at the store, the organisms inside are in a state of inactivity so they don't need to eat (keeping them cool and dry helps keep them preserved this way). But when you mix them into dough, they wake up and begin eating—and making carbon dioxide.
When you buy a packet of baker's yeast at the store, the organisms inside are in a state of inactivity so they don't need to eat (keeping them cool and dry helps keep them preserved this way). But when you mix them into dough, they wake up and begin eating—and making carbon dioxide.
When you make yeast-based bread, you often have to wait for it to rise. During this step the dough might appear to be growing. But what is really happening is that you're giving the tiny yeast organisms time to eat and create small pockets of carbon dioxide inside the dough, which is what makes the dough seem to grow larger—and which leads to fluffy bread! (Bread products that don't have yeast rise during baking thanks to other ingredients, such as baking powder.)
Why do the yeast organisms "wake up" when you put them into a dough mixture? Like other living organisms, they need food and water. So by putting them in a moist environment with nutrients (such as sugar), they become "active."
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