Why does yeast make bread rise and bubble?

The smell of earthy bread and its crusty sliced end with a thick slab of butter with a piping hot cup of brewed coffee with surely make your mornings beautiful. Whether it’s a muffin or a bun, a nicely baked bread is manna from heaven, no matter what time of the day. And sure enough, as the British journalist William Cobbett puts it, “without bread, all is misery.”

Bread is a food that unites most of the civilizations around the globe. It is prepared in a thousand different forms in every distant part of the world. Whether it’s a carbo-loaded white bread or health-buff approved wheat, bread is a staple in our diet. It contains carbohydrates which pumped people with energy to face the day. It also has proteins, salts, and essential vitamins for the proper functioning of the body.

The bread-making process originated in ancient times. The Egyptians are already baking as early as 2000 BC. Their basis is to mix flour with other ingredients like water, fat, salt, and some ingredients that give aeration followed by baking. Their bread making practice was to use a little old dough to “start” the new dough. The two doughs were then mixed and allowed to rise for a couple of hours before baking. (click here for more details)

Every country and culture has shared with the world its type of bread. The Australians have a signature damper, a wheat-based white bread baked in coals. While the steamed buns made with flour reminds us of the  Chinese. With love for banana bread, the US celebrates February 23 as the National Banana Bread Day. Nothing else in the bread family can bring the images of the iconic Eifel Tower and all things French, the way baguette does. Hats off to the boot-shaped country Italy, where pencil-thin appetizer stick bread hails. Stick bread is sometimes served soft and warm topped with cheese and garlic. The Jews made the golden, soft-as-a-pillow braided bread made of eggs, challah. The soft and round leavened bread pita originated in the Middle East some 4000 years ago. The Germans created the pumpernickel, a type of flavorful rye-bread made with coarsely ground rye berries. Courtesy to the Emerald Isles, the world has tasted the most legendary soda bread made of soft wheat flour, buttermilk, baking soda, and salt. The Egyptians invented the sourdough, as its name implies, a bread with a typical slightly sour flavor. (click here for more details)

Bread can be grouped in three main types: those that rise higher and needs to be baked in pans, those with a medium volume like French bread, and those that hardly rise at all or flatbread.

We will not be enjoying a bunch of leavened bread if not for the discovery of yeast. And we owe a huge debt of gratitude to Macedonian bakers, who, while taken as slaves to Rome, introduced the art of making leavened bread. What is the driving force that causes bread to rise?

Yeast! It is a single-celled fungus related to a mushroom, whose cells are still alive when you mix it with dough. Yeast needs to eat, and it loves sugar. Among the 150 species of yeast, we used mostly just one in bread making – Saccharomyces cerevisiae (“sugar-eating fungus”). This little organism helps in the magical process called fermentation, allowing a mass of dough to become a well-risen loaf of bread. During this process, yeast feasts on sugar and burps carbon dioxide and alcohol into existing bubbles in the dough. The bubble trapped within the dough will begin to inflate it, just like someone blowing a balloon. The more the sugar the yeast eats, the more gas that is formed, and the higher the bread rises. (click here for more details)

Aside from yeast’s ability to make bread rise, it also helps strengthen the dough. Stirring together flour and water makes the two proteins (glutenin and gliadin) in flour grab water and each other. These proteins then form a bubblegum-like mass of molecules called gluten. In bread making, developing more gluten strengthens the dough and holds in gases that will leaven the bread.

The development of flavor happens when the dough is chilled, as the yeast’s activity is reduced at cold temperatures. While the yeast is still sleeping, it’s time for the bacteria to thrive, producing many flavorful acids that make our bread delicious.