Now more than ever, we turn to carbs for comfort during this pandemic. Taking my place among the growing brood of pandemic bread bakers, I set my sights on making soft dinner rolls from scratch. Since I spent most of the bread-making process idly waiting for the bread to rise and then bake, I had time to think about the real bread-winner in this recipe: the yeast.
Before and after images of the dough rising. Look how much the yeast has made the dough rise in only one hour!
Specifically, I wondered:
How is dry yeast manufactured?
How does yeast make bread rise?
If yeast and mold are both fungi, what is the difference?
How is dry yeast manufactured?
The production of yeast begins with a small culture of yeast called seed yeast that is maintained under controlled conditions so that wild yeasts from the environment do not interfere.
The next step multiplies the small culture of seed yeast into huge vats of stock yeast in a process called cultivation. Under conditions controlled for temperature, pH, and vitamin and nutrient availability, the yeast are fed cane or beet molasses and are aerated to promote rapid division of the yeast cells. The brand of yeast I used, Red Star Yeast, cultivates the yeast in tanks as large as 40,000 gallons!
After the yeast is mass produced in the giant tanks, centrifugal pumps isolate the yeast from the culture medium in which the yeast cells had cultivated.
The yeast is concentrated, filtered, finely extruded and cut into granules, and dried into dormancy at high temperatures. Then, the dried yeast is either vacuum packed or packed under nitrogen to keep out unwanted oxygen and moisture, preserving the shelf-life of yeast until it is ready for the use by bakers.
How does yeast make bread rise?
The yeast in a packet is “activated” by rehydrating it with a liquid. In the recipe I used, I stirred it in warm milk and white sugar, both upon which the yeast feeds. The yeast metabolizes the sugars in two ways: respiration and fermentation. When oxygen is present, the yeast undergoes respiration and produces carbon dioxide as a byproduct, which is trapped by the gluten in the flour. After the oxygen in the dough is depleted, the yeast switches over to fermentation (aka anaerobic respiration) and produces ethanol alcohol, contributing to a beer-like aroma. As the bread bakes, bubbles of carbon dioxide and evaporated alcohol and moisture leave behind fluffy, airy bread.
If yeast and mold are both fungi, what is the difference?
Yeasts and molds can be both harmful and beneficial. Think bread yeast vs athletes foot or blue cheese vs moldy bread. The main difference is that yeasts are unicellular while molds are multicellular and occur in long filaments known as hyphae.
When you see a fuzzy mold spot on a slice of bread, you should not eat the rest of the bread because the hyphae have likely spread throughout the whole loaf, invisible to the naked eye.
Making Soft Dinner Rolls
If you would like to make your own soft dinner rolls, I highly recommend this honey-butter glazed roll from Sally’s Baking Addiction. It turned out perfectly- pillowy, warm, and buttery!
Because I was in a hurry, I jump started the proofing of my bread by placing it in a slightly warmed oven. Doing so shortens the rising process because the yeast’s metabolism increases at higher temperatures (i.e., higher metabolism equals more gasses produced). I managed to shorten the rising process by an hour in time for my family to eat these for dessert!
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