Leavening Legends and Cultural Creations

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There are three preindustrial systems for leavening breads: steam; pure cultures of yeast; and yeasts and bacteria working together in sourdough starters. Steam is the simplest leavening system. Bake a thin disk of dough on a hot surface and it’ll puff up like a ball. Loaf breads are too thick to be steam-leavened. You can test that yourself by mixing up a dough of flour and water and baking it in a bread tin. A mixture of flour and water has no taste, is the recipe for glue, and makes a loaf bread that’s an inedible brick. Loaf breads only become easy to bite into, beautiful to look at, and lovely to eat because they’re fermented.

Fermentation is magic. Fermentation is what brings flavor, aroma, and a light crumb to loaf breads. Prior to the development of chemical leavenings, making a loaf bread without the help of yeast wasn’t possible. Baking soda, along with other industrial leavenings, aerates bread, but doesn’t change the underlying flavor of the dough. Chemical leavenings aren’t robust enough to create breads with large air holes in the crumb. They also don’t make breads taste good. Fermentation is required to make a richly flavored bread with large air holes. Pain de campagne, for example, can only be made with yeast, either in the form of pure strains purchased in packages or with the wild yeasts and bacteria that colonize sourdough cultures.

According to confirmed archeological research, the oldest bread excavated so far was made 14,400 years ago in what is now Jordan. This was thousands of years before the first farmers, so these breads were made with wild wheat and barley. These early breads were made from sifted flour worked into a dough and baked directly on embers or super-heated ground. The technique of ember-baking flatbreads is still common in Rajasthani villages, and ground-baked flatbreads are still common among the Bedouins in Sinai and North Africa. This early method of baking is described in the Bible, in the Gospel of John:

As soon then as they were come to land, they saw a fire of coals there, and fish laid thereon, and bread. John 21:9

Whether you bake your disk of unfermented dough over glowing embers or in a hot wood-fired oven, the bread’s character and taste will be created by the light browning of the crust. Fermented breads also get flavor from their crusts; the flavor of the crumb comes from the fermentation process itself.

Leavening or Fermenting?

To make a palatable loaf of bread, you have to fill it with air holes. Fermentation creates the CO2 that’s trapped within the dough’s gluten structure, providing bread its open crumb. Fermentation also lowers the dough’s pH, giving it taste, and creates flavors that give it a lovely aroma. Sugar-loving yeasts are always the primary agents of dough fermentation. The name of the yeast most commonly associated with bread fermentation is Saccharomyces cerevisiae. This is the yeast that’s freeze-dried and sealed into convenient packets; a majority of the time, it’s also the dominant “wild” yeast in sourdough starters. Remarkably, S. cerevisiae is also the workhorse that ferments grains and fruits for beer and wine. While different strains of S. cerevisiae are associated with bread, wine, and beer, all the strains are more or less interchangeable, meaning you can make beer, wine, or bread with any one of them.

If you go online to look at yeast suppliers for brewers, winemakers, and bakers, you’ll quickly see that brewers and winemakers approach yeast differently from bakers. They’re focused on how different strains of yeast produce interesting flavors in their beverages. Bakers are primarily interested in how efficiently yeast strains produce CO2. Bakers have traditionally used yeast for practical reasons. Breads made with 1 to 2 percent dried yeast by weight of flour can be out of the oven 4 to 6 hours after starting. This compares with the 16 hours or more required for a batch of bread using a sourdough starter. Breads that are yeast-fermented for expediency tend to have a soft crumb and a neutral flavor. But it doesn’t have to be that way. When bakers cut back on yeast, or lower the fermentation temperature, then, in addition to producing CO2, the yeast has time to produce flavors within the dough, and also to further lower the dough’s pH, which adds complexity to its taste profile. The crumb also becomes chewier. Slow-fermented yeasted breads can have taste profiles similar to many sourdough breads. I encourage you to order yeast from wine and beer yeast suppliers to see how different yeasts might affect your breads. Start experimenting by cutting yeast back to no more than ¼ teaspoon per pound of flour — roughly 3½ cups — and giving it 12 to 48 hours to ferment. A good way to develop flavor with yeast is to use a pre-ferment starter, such as a poolish. “Poolish” is a fermented batter made with a couple of pinches of yeast and 1 cup each of flour and water, and left on the counter overnight.

The scientific name, Saccharomyces cerevisiae, is its own mnemonic. “Saccharo” means sugars in Latin, reminding us that this is a sugar-loving organism; and its second name is close to cerveza — “beer” in Spanish— making it easier to remember that it’s a sugar-loving organism associated with fermentation. This multitalented yeast is a semi-domesticated organism. Being semi-domesticated means that, like cats, it seems to have adopted us without changing all that much from its wild progenitors. In a sense, both cats and this species of yeast adopted us for the same reasons. The foods we store and process around our dwellings attract the kinds of foods these creatures like to eat — cats eat small birds, mice, rats, and snakes, and yeast organisms eat the sugars associated with grains, fruits, bread doughs, and fermenting beverages. The yeasts also discovered that they could thrive inside our bodies by helping us digest sugars. Yeast is our friend. It’s part of our human ecology.

Gray Sludge, God’s Good

Historically, beer-making cultures, such as the British, favored yeasted breads, while winemaking cultures, such as the French, tended to favor sourdough breads. Our contemporary discussion about “natural leavening,” the healthfulness of sourdough over yeast, and the bias many of us feel in favor of sourdough, tends to have its origins in French ideas about bread and what makes it good or bad. For centuries, French bread writers have been extolling the virtues of sourdough and talking down yeasted breads. France is the world of wine, not beer. There wasn’t a village brewer to go to for yeast, so they perfected sourdough.

Our own Anglo-American culinary tradition recognized yeast as a miracle product. Well into the 1600s, “God’s good,” was one of yeast’s synonyms. People had no idea what it was scientifically, because they didn’t have the microscopes needed to actually see individual yeast cells. Thus, they had a mystical answer to the question, “What is this gray substance that both leavens bread and makes a grain mash and fruit juice alcoholic?” It was God’s good. While people didn’t know that yeast was a budding fungus until the second half of the 19th century, they knew where to find it and how to use it, which is all that ever really mattered to bakers.

Historically, if you didn’t brew your own ale, then you went to the brewer and bought some of the gray sludge that could be skimmed off the top of fermenting ale, or that was left at the bottom of the vat after the ale had been drawn off. A late 18th century American term for yeast was “emptins.” People had an empirical understanding of how to use it. Yeast works most efficiently when the dough is near 75 degrees Fahrenheit. Depending on season, old bread recipes specify mixing dough with water that ranged from warm to hot. They also almost always used a pre-ferment. In early British and American recipes, the pre-ferment was called a “sponge.” It was a batter made of mixed up yeast and flour. More flour was sprinkled on top, and was left to ferment until the flour showed signs of active fermentation, at which point the rest of the flour, water, and salt was added to the dough. Pre-ferments are always the best way to get flavor out of yeast.

Getting a Rise out of Taste

Sourdough starters are well-understood by scientists, but poorly understood by most bakers. There’s a lot of myth and mystification. In many ways, sourdough is today’s God’s good. We may not be certain exactly what it is, but we love what it does. What’s helpful to understand is that sourdough starters consist of a harmonious colony of Lactobacillus bacteria and sugar-loving yeasts in a ratio of roughly 100 bacteria to 1 yeast. It’s the yeasts that produce the CO2 that gets trapped in the dough. The lactobacilliproduce lactic acid, which gives sourdough the potential to make a more sour-tasting bread than one only leavened with yeast. The slower fermentations characterized by sourdough leavens also mean that both the yeasts and the bacteria have time to trigger cascades of biological processes that produce attractive flavors. It’s the combination of bacteria and time that enables sourdough breads to develop such complex taste and aroma profiles. Sourdough bacteria are also thought to make subtle changes to the dough that, for example, improve its keeping qualities and lower its glycemic index.

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While yeast alone can’t take doughs to the lower pH levels that are possible when they’re working in concert with their lactobacilli partners in starters, whether or not a dough tastes sour has more to do with dough management than whether it’s leavened with yeast or sourdough. For the bakers reading this, if the total amount of starter in your dough is in the range of 5 percent, the dough won’t taste sour, but if you start with 30 percent, it will taste sour. The more frequently you refresh a starter — three times per day, for example — the less sour it’ll taste. The more mineral content in the flour used to make the starter — “ash” in baking vocabulary — the stronger the sour will be. Thus, a rye starter produces a bread that’s more sour than one made with a white flour starter. If you make a yeasted bread, but let the dough ferment in the refrigerator for several days, it’ll develop a flavor close to a mild sourdough.

Cultural Fervor and Leavening  

Where there’s magic, there can also be controversy. Historically, cultures that favor beer have also favored yeast and denigrated sourdough, while countries such as France have celebrated sourdough (though not sour-tasting breads) and explicitly rejected yeasted breads as inferior. This cultural divide is clearly demonstrated by this late 19th century American trade card for Warner’s “Safe Yeast” (left). The trade card captures a centuries-old critique of sourdough by Anglo-American yeast bread culture: Sourdough was thought to cause indigestion and lead to bad health. It was decades after the germ theory of disease was discovered in the 1860s that this misunderstanding was finally put to rest. Previously, the idea that sour bread could make you sick was disseminated in medical texts, which blamed sour foods, including sour bread, for gastroenteritis.

Today, we have an inversion of this particular historic Anglo-American attitude. Sourdough breads are now widely considered to be more authentic and natural, to have a preferable taste, and to provide probiotic and other health benefits. Stand in any line in an artisan bakery, and it’s clear that many people eschew the yeasted breads so easily available in grocery stores. Chad Robert’s wildly popular book Tartine provides the recipe for his bakery’s star bread, which would’ve been a commercial failure had that bread been yeasted. We rarely think of bread in terms of fashion, nor do we tend to think of ourselves as bread fashionistas, and yet. The recipe for the best bread isn’t written in the stars. It’s written in our hearts.

Best Bread: Yeast Packet or Starter?

Yeast alone, or along with the bacteria in a sourdough starter, offers each of us a lifetime of experimentation. There isn’t a best leavening true for all time, just as there isn’t one bread best for every meal. Pure strains of yeast and sourdough starters have been around for thousands of years. They’re both ancient and integral parts of the loaf bread tradition. Neither is better than the other. Each has its strengths. The last couple of decades have seen a fantastic creative focus on sourdough breads. If this same intensity of focus and creative energy were to be focused on yeasted breads, I think we’d all be astonished at what could be created. Bread is an invention. It isn’t an agricultural crop. Yeast and sourdough are both gifts. They’re both God’s good.

William Rubel has been baking bread since he was 11 years old, and he enjoys an improvisational approach to baking, often using his outdoor oven to test traditional recipes. He’s the author of Bread: A Global History, and is one of the world’s preeminent bread historians.

Published on Nov 19, 2019


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