Review Answers for Breads and Batters Lab 1. What makes bread rise? The pressure of expanding gas (from a leavening agent) pushing against gluten fibers causes bread to rise. 2. Why do whole wheat breads rise less than white breads? Whole wheat flour is more dense than white flour, so whole wheat breads rise less. FYI: Wheat flours form more gluten than other flours such as rye and soy, so it is necessary to combine wheat flour with other flours to get an acceptably porous loaf of bread. 3. List the three types of natural leavening agents. 1. air 2. steam 3. carbon dioxide 4. What is yeast? Yeast is a microorganism (Saccharomyces cerevisiae) that gives off carbon dioxide as a byproduct of fermenting carbohydrates. 5. What three things does yeast need to do its work in baking? Under these conditions, what does yeast produce? 1. carbohydrates (starch in flour and/or sugar) 2. water to allow it to rehydrate 3. time to digest the carbohydrates Under the right conditions, yeast produces carbon dioxide. 5. Why do you need to knead yeast bread dough? 1) to develop gluten from the glutenin and gliadin precursors in wheat flour 2) to incorporate air into the structure 3) to disperse the yeast throughout the dough Also, kneading dough is good exercise for your wrists and is very relaxing! 6. What does it mean to "proof" yeast? "Proofing" yeast means to provide yeast with needed warm water, carbohydrate, and time to work, and wait to observe the little bubbles that indicate that gas is being given off, "proving" that the yeast is alive and working. 7. What is gluten? How does it function in baking? Gluten is a protein complex that develops from manipulating glutenin and gliadin (and a liquid). Gluten becomes elastic, enabling it to stretch under the influence of a leavening agent, providing structure to breads. The structure hardens when heat finally denatures the proteins, producing a nicely shaped bread. 8. What does it mean to "proof" dough? "Proofing" dough means to allow it to rise before baking. This increase in volume "proves" that the leavening agent (carbon dioxide) is being produced and is stretching the gluten strands properly. 9. What is baking soda? Baking soda is NaHCO3--sodium bicarbonate, which is a basic (alkaline) ingredient. 10. What other ingredient is needed in a bread recipe that relies on baking soda for leavening? The combination of a base and an acid results in a salt plus water and carbon dioxide as byproducts. Since baking soda is a base, it is necessary to add an acid to any recipe relying on baking soda as a leavener. The acid might be cream of tartar or be a naturally acidic ingredient/flavoring in the recipe. 11. When an acid and a base are combined, what byproducts are produced? An acid and a base produce a neutral salt plus water and carbon dioxide as byproducts. The carbon dioxide is the actual leavening agent. 12. What is baking powder? Baking powder is a self-contained combination of an acid (often cream of tartar) and a base (baking soda). Double-acting baking powders contain two acids, generally one that acts at room temperature and one that acts at oven temperatures, providing extended leavening action. FYI: baking powders usually contain an additional ingredient such as cornstarch, which both absorbs moisture and acts as a filler to keep the acid and base from reacting in the can. 13. What is the difference between bread flour and all-purpose flour? Bread flour is relatively coarse and gritty, made from hard wheat, and tends to work exceptionally well in developing gluten in yeast breads. All-purpose flour is relatively fine and powdery (though not as fine and powdery as cake flour) and is good for a wide range of uses. 14. What is the difference between self-rising flour and all-purpose flour? Self-rising flour is flour that has baking powder/baking soda plus an acid already added to it. So if self-rising flour is used instead of all-purpose flour, any baking powder or baking soda called for in the recipe should be eliminated.