Mr. Joanis’ Science Class! Name: ________________ Period: ____ What is Yeast? Maintaining Your Own Sourdough Starter Yeast, simply put, is a fungus. What separates yeast from other fungi like the mushrooms that you might find on a pizza or in the stomach of a mustachioed Italian plumber is that yeast is single-celled. All of the different varieties of yeasts are single-celled organisms, as opposed to all other forms of fungus which are made up of more than one cell. The yeast that you might buy at a grocery store is actually a specific species of yeast called Saccharomyces cerevisiae, which is Greek for “sugar-fungus of beer.” S. cerevisiae isn’t the only yeast that can be used for breadmaking, though. Although it is widely used, other wild yeasts can serve the same function we use S. cerevisiae for in the breadmaking, brewing, and other fermenting processes: creating carbon dioxide gas. In breadmaking, yeast serve as a leavening agent – a substance which leavens or makes bread rise. Yeast isn’t the only leavening agent; baking powder is one other substance that can cause bread to rise while baking, and more exist beyond just those two. The carbon dioxide gas that yeast produces gets created when yeast cells break down the carbohydrates in flour. In order to become more familiar with the action and uses of yeast, you will be creating and looking after your own sourdough starter. A sourdough starter is an actively fermenting (creating carbon dioxide gas by breaking down carbohydrates) mixture of flour and water. Sourdough starters are used in the baking of sourdough bread. The fermentation in a sourdough starter occurs as a result of the presence of wild yeast cells that are naturally present in flour. The goal of creating a sourdough starter is to allow those naturally occurring yeasts to multiply. After a sourdough starter is packed with yeasts and other microorganisms, it can be used as a substitute for baker’s yeast in any bread recipe as a leavening agent. In addition to leavening bread, sourdough starters are slightly acidic and change the flavor and chemical profiles of bread. Follow the instructions below and answer the questions that follow: Materials: Water ½ cup of flour Plastic container with snap-on plastic lid (example pictured right) o You can wash and repurpose an old food container o The container should be able to hold at least 2 cups of fluid Spoon for mixing Joanis - 4/21/2020 δ Procedure: Day 1 . Mix 3 tablespoons and 1 teaspoon of flour with ¼ cup of slightly warm water in a plastic container until it has become a sloppy paste. Cover the container with a lid or plastic bad to prevent from drying out, and store in a warm place. Day 2 . Mix 3 tablespoons and 1 teaspoon of flour with ¼ cup of slightly warm water into your existing paste-y mixture. Return it to its warm place. Day 3 . Mix 3 tablespoons and 1 teaspoon of flour with ¼ cup of slightly warm water into your existing paste-y mixture. Return it to its warm place. Day 4 . Mix 3 tablespoons and 1 teaspoon of flour with ¼ cup of slightly warm water into your existing paste-y mixture. Return it to its warm place. Observations: 1. Describe the sourdough starter after mixing it on Day 1. 2. Describe the sourdough starter after mixing it on Day 2. 3. Describe the sourdough starter after mixing it on Day 3. 4. Describe the sourdough starter after mixing it on Day 4. δ 5. Describe the sourdough starter after coming back to it on Day 5. 6. Do you think that the yeasts in the flour were still alive by Day 5? Why or why not. 7. What is yeast? Moving Forward: After your sourdough starter’s 5th day, you can do any of the following things with it… Give it away. Use the whole thing in a bread recipe (you can use your entire starter as a substitute for 1 tablespoon of yeast, ¾ cup of water, and 1 cups of flour). Use two-thirds of your starter in a bread recipe, and conserve the rest (re-grow your starter by repeating the steps in Day 2 through Day 4). Freeze it and use it later. .