The Science Behind: Yeast

If you look in the fridge or pantry of a baker, you may find some living, single-celled microorganisms — or, as they are more commonly called, yeast. Yeast has many different strains,— or types — the most common one being Saccharomyces cerevisiae. These different strains are bred for gas production and the flavor they will produce. So, if you want to be super classy, you could breed your own yeast strain, name it, create some seriously special breads, and establish your own unique chain of bread bakeries. Or, if you’re like me, you can grab the cheapest box of yeast from the store and keep making your humble loaves of bread.

Above are the three main types of yeast (from left to right): cake yeast, active dry yeast, and instant yeast(Image Credit: Bread, Cakes and Ale).

There are three main types of yeast: instant/quick-rise yeast, active dry yeast, and cake/fresh/compressed yeast, and they all result in different flavors, last for different amounts of time, must be moistened in some way to work, and demand personal treatment. Instant yeast — also known as quick-rise yeast — is a smaller form of dry yeast that can be added directly to dry ingredients without having to soak it beforehand. Active dry yeast is partially dehydrated yeast that is formed into granules. To use active dry yeast, you must soak it with warm water and a pinch of sugar before adding it to the dry ingredients. Cake yeast — also known as fresh or compressed yeast — is made from a mix of yeast and water that has enough moisture for it to be compressed into blocks. Apparently, professionals swear that cake yeast is the bomb-diggity when it comes to flavor. However, cake yeast is very expensive, only lasts about two weeks, and is hard to find in the United States.

Two other ingredients that affect yeast growth are salt and sugar. Salt calms down the yeast’s growth rate and sugar feeds the yeast. It’s like relaxing in a bath of waffles. You have food, and you can relax. However, like all great things, too much salt or sugar will hurt your dough (Image Credit: Giphy).

But how does yeast make stuff poofy? First things first, you need flour, water, and yeast. When these three essential ingredients are mixed, enzymes in the yeast cause starch molecules in the flour to break down into simple sugars so they can be used for energy. As you continue to mix and knead the dough, tiny air bubbles are trapped and dispersed throughout the dough. As your dough sits, the yeast uses energy from the sugars it consumes to survive and reproduce. The byproduct of this is carbon dioxide and alcohol. This process is called fermentation. These byproducts go into the premade air bubbles and cause the dough to rise, but if your bread has a weak and not-so-stretchy gluten network, then the byproducts won’t be able to form as many large bubbles.

If you use too much yeast, your bread won’t taste too great. The amount needed depends on the temperature the bread will be at as it rises and how long it will be rising. If the bread will rise for a short time and/or be in a hot place, more yeast will be needed. If the opposite it true, you can use less (Image Credit: BBC Good Food).

The time it takes for bread to rise varies greatly from recipe to recipe. The main way to mess with the time it takes for a loaf of bread to rise is by changing the temperature it rises at. By increasing the temperature, you speed up the yeast. However, if you do this, the yeast won’t work as well and the bread won’t taste as good. By lowering the temperature, you calm down the yeast, causing it to slow down. This gives the bread more time to develop flavor. This extra flavor development can be blamed on bacteria. As the dough rises at room temperature, the yeast hogs all the sugar, leaving nothing for the bacteria. But when the yeast is slowed down, the bacteria has a chance to finally feed itself, leading to more flavors.

In most recipes, bread dough rises twice. During the first rise, heat and alcohol build up in the center and the yeast is packed into clusters. When the dough is punched down or stirred, the hot and cold spots are evened out, the alcohol buildup is released, and the yeast clusters are broken up (Image Credit: Reddit).

Flavor is also developed as enzymes in the yeast break down starch molecules. As the yeast consumes the sugars, it produces carbon dioxide and alcohol, as I mentioned before, but it also produces organic acids and amino acids, which are tasty. In addition to adding flavor, the acids and carbon dioxide in the dough also make it more acidic, which causes even more chains of molecules to break into smaller ones. This creates flavor because when molecules in protein, starches, and fats are broken down into their building blocks they become delicious.

Like all organisms, yeast can die. When opening a container or packet of yeast, it should smell earthy, and, well, yeasty. If it doesn’t, you can make sure it’s still alive by combining it with warm water, a pinch of sugar, and some flour. After some time, the mixture should grow (image Credit: Imgur).

When the dough is at last put in the oven, the carbon dioxide expands and moves through the bread, and the alcohol begins to evaporate, transforming into gas bubbles that help the bread rise. The alcohol’s evaporation also results in the mouth-watering aroma that wafts from bread. Researchers at the University of Southern Brittan in France found that when people walked by a bakery with this aroma in the air, they were more likely to help a stranger than those without the aroma in the air. Now that you have a reason to make bread, it’s time to bake. You’re welcome.

Works Cited

Corriher, Shirley. “Yeast’s Crucial Roles in Breadbaking.” Fine Cooking, no. 43, Mar. 2001. Fine Cooking, www.finecooking.com/article/yeasts-crucial-roles-in-breadbaking. Accessed 23 Sept. 2017.

Douglas, Julie. “Why do I need yeast to make bread?” How Stuff Works, Stuff Media, 14 June 2013, www.stufftoblowyourmind.com/blogs/yeast-bread.htm. Accessed 23 Sept. 2017.

Joachim, David, and Andrew Schloss. “The Science of Baking with Yeast.” Fine Cooking, no. 127, Feb.-Mar. 2014, pp. 24–25. Fine Cooking, www.finecooking.com/article/the-science-of-baking-with-yeast-2. Accessed 23 Sept. 2017.

Lawandi, Janice. “The Science Behind Yeast and How It Makes Bread Rise.” Kitchn, Apartment Therapy, 15 Dec. 2015, www.thekitchn.com/the-science-behind-yeast-and-how-it-makes-bread-rise-226483. Accessed 23 Sept. 2017.

McGavin, Jennifer. “What Bakers Should Know About Yeast.” The Spruce, 13 June 2017, www.thespruce.com/bread-making-yeast-faq-1447197. Accessed 23 Sept. 2017.

Thomson, Julie R. “So What The Hell Is Yeast, Anyway, And How Does It Work?” HuffPost, Oath, 10 June 2014, www.huffingtonpost.com/2014/06/10/yeast-all-about-_n_5473635.html. Accessed 23 Sept. 2017.

— Isabella S., Pennsylvania

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