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Home Ec: The Science of Yeast

I LOVE bread. A tradition of making it from scratch is easy to establish. The aroma of this yeasty wonder baking is pure gratitude and a warm slice with butter is a one-of-a-kind head-nodding smile. But home baked bread is more than yummy, it's science! Of course yeast is the agent that makes bread rise and yeast is an interesting thing to study.

Yeast has several crucial roles in bread baking. Yeast is a single celled fungus. How can such a little fungus be so important? Well, yeast is the driving force behind fermentation that allows a big lump of dough to become well risen. Yeast is a living organism that works by consuming sugar and excreting carbon dioxide and alcohol. Fermentation helps to strengthen and develop gluten in dough and also contributes to incredible flavors in bread.

There are three essentials to any bread dough: flour, water, and yeast. As soon as these are stirred together, enzymes in the yeast and the flour cause large starch molecules to break down into simple sugars. The yeast then eats the sugars and exudes a liquid that releases carbon dioxide and alcohol into air bubbles in the dough. It’s just like blowing up bubblegum! The longer fermentation goes on the more it breaks down big molecules in proteins, starches, and fats into their building blocks, so the more flavorful the dough becomes.

There are two basic yeasts that we buy today: active dry yeast and quick rise, or instant yeast. You can use either in a recipe. You just need to mix the active dry yeast with warm, (not hot) water with a pinch of sugar to activate it. Instant yeast can be added directly to the flour with all the other ingredients. This recipe calls for instant yeast and I don’t happen to keep that on hand so I used my active dry, I just added it to the warm water and let it sit for a few minutes until bubbles formed on top which lets me know the yeast is alive. If bubbles don’t form it means your yeast is expired or you killed it with hot water! About 105 degrees is perfect for dissolving yeast.


Flour is an important ingredient in bread making. The higher the quality the better your bread will taste. It’s better to use bread flour rather that all-purpose. Here’s why. Bread flour is milled from hard red spring wheat. It has a higher protein content so it has more gluten and will rise higher. All- purpose flour is great for soft breads like muffins and banana bread. It will give a more tender crumb.

Water is the last basic ingredient so it should be pure as well. If it has too many chemicals in it, that can be hard on the yeast and doesn’t taste good either.

Today I went to my favorite site for bread recipes, King Arthur Flour and found just what I was looking for. It is quite easy…a yummy and satisfying, not to mention educational, Thanksgiving activity for the whole family!

Soft Rolls

4 1/2 plus 2/3 cup bread flour
2 1/4 teaspoons instant yeast
2 tablespoons sugar
2 teaspoons salt
2 large egg whites
¼ cup vegetable oil   
1 1/2 cups lukewarm water
3 to 4 tablespoons sesame seeds
1. Mix and kneed the dough ingredients-by hand, mixer or bread machine set on the dough cycle—to make a smooth dough.
2. Cover the dough and let rise until it’s noticeably puffy, about 60 to 90 minutes.
3. Transfer the dough to a lightly greased work surface, deflate it, and divide it into 12 pieces (about 3 1/4 ounces each). Shape into balls.
4. Dip the top half of each roll into water, then into the seeds. Place rolls onto a parchment-lined baking sheet. Press gently to flatten.
5. Cover the rolls, and let them rise until puffy, 45 to 60 mins. Towards the end of the rising time, preheat the oven to 400F.
6. Bake the rolls until they’re deep golden brown, 22 to 26 mins. Remove and cool on a rack.

– Sara

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