Sourdough Hands: How Bakers And Bread Are A Microbial Match

Lindsay Patterson wrote . . . . . . . . .

If you bake a lot of sourdough bread, your hands might look like your loaves. Bacterially speaking, that is. The microbes found on bakers’ hands mirror the microbes within their starters — the bubbly mix of yeast, bacteria and flour that’s the soul of every loaf.

That’s the surprising finding from a sourdough bake-off experiment, coordinated by ecologists Rob Dunn and Anne Madden. Fifteen sourdough experts from around the world arrived at a Belgian baking center with brand-new homemade starters, fed from the exact same ingredients sent from Dunn’s lab. But before the bakers could get their hands into the dough, they held them out to Madden for bacterial swabbing.

Partnered with analysis of the starter’s microbial ecosystem, Dunn and his collaborators were able to draw a close connection between bread, bakers and their bacterial species.

“It’s a reminder that we have a really intimate relationship with our food,” says Dunn. “Not only do we impact the species in our food, but the species in our food impacts the species on or in our bodies.”

In his new book, Never Home Alone, released Nov. 6, Dunn explores the species behind what he calls the “wild life” of our homes. “There’s a lot more life in our houses than we think,” he explains. “To the extent that we’ve thought about it, we’ve tried to kill it.”

It’s no surprise, then, that Dunn’s survey of indoor species (including insects) lands him in the bakery with sourdough, which is brought alive by microbes. The experiment delves into how cooking with fermented foods might affect the microbes of the people who make them. In the book, Dunn describes how he formed the hypothesis that our bodies and environments influence the taste of our food.

The following interview has been edited for brevity and clarity.

Where did the idea that hands and home affect the flavor of food come from?

I had a couple of conversations that led me toward this concept of son-mat, the Korean word for "hand flavor," that there was something that the hands offered to the food. If I were a poet, that would just be "love" and "sentiment." But I'm an ecologist. So the only thing I could think about in the context of that word was that there were actually species moving from people's hands into the food. And if there were species moving from hand, there must also be species moving from homes. The boundary between the body and the home is super fluid.

How did you come up with an experiment to test that idea?

We teamed up with the Puratos Center for Bread Flavour, which is a super cool bread museum, research and conference center in the tiny German-speaking part of eastern Belgium. The ideal experiment would have people from different regions, both men and women, from different styles of bakeries. That would maximize the kinds of ways that their bodies and bakeries might influence what they were contributing. That’s where Puratos was super helpful, because they were able to recommend bakers around the world who could come together at this bread center to do the experiment. The hope was to get them all to make the same starter except for the microbes, then bring them together, and all make the same bread. So we could test the starter, we could test their hands, and we could test the consequences for the bread itself.

What were the results?

The starters were super different, and those differences were in part associated with who made them, and where they made them. There was an essence of the baker in the starter the baker made, and that was conveyed in the bread. That was one result.

The other one, which our design wasn’t perfect for, but was the crazier one to me, was that we’d swab the hands of the bakers to figure out what was on their hands, and it was the same thing that was in the starter. We hadn’t thought to wonder if the baker’s hands themselves would be unusual. But lo and behold, the baker’s hands looked like sourdough. So yes, the bakers did influence their starters, but the other way around was true too. The life of baking seems to influence the bakers.

Can you describe what you mean by “Their hands looked like sourdough”?

The most common sourdough starters are lactobacillus bacteria and their relatives. And the most common yeasts are saccharomyces yeasts and their relatives. If we look at the average human hand, those bacteria and those yeasts are really quite rare — three percent maximum of fungi on the hands. On the bakers, they were in some cases up to 60 percent of the bacteria in particular on the hands. Which is to say that the hands looked more like sourdough in terms of the microbes they had more than they looked like the hands of the plumber or the professor.

So, based on their bacteria, if you were to try to pick sourdough hands out of a lineup, those hands might look like the starter itself?

Yeah, they would probably look like a funky starter.

People have such a personal connection to their starters. Would you say that that’s backed up by the science at this point?

Yes. Clearly, our data suggests that something about baking seems to be changing the hands of the people who do the baking. To me, it suggests that your hands are in a way taking a measurement of your life. Right? And so if it’s a life spent with your sourdough starter, if it’s a life spent in food, they’re going to record a different story than if it’s a life just swiping left and right on your phone.

How much bread do you have to bake to have sourdough hands?

That’s a good question, and I don’t know the answer. But if I were to speculate, I bet it doesn’t take a lot of baking to change your hands a little bit. But if you really want those total baker hands, I think that’s touching bread as much as you touch people.

Source: npr


The Biology of Sourdough

Patricia Gadsby and Eric Weeks wrote . . . . . . . .

About 34 years ago, Frank Sugihara recalls, he and Leo Kline, a fellow microbiologist, set out to “solve the mystery of San Francisco sourdough.” The two scientists were working with baker’s yeast in a Bay Area lab run by the U.S. Department of Agriculture, so perhaps it was inevitable they’d wind up studying San Francisco’s signature bread. This crusty loaf, with its chewy bite and sharp acidulated tang, was a long way from Wonder Bread, and few tourists left the airport without a loaf. Local lore attributed the bread to Basque migrants from the Pyrenees who arrived in San Francisco during the gold rush. Local bakers swore that no one could reproduce it outside a 50-mile radius of the city. When they gave dough to bakeries elsewhere, it inexplicably lost its “sour.” But was it—is it—truly unique?

Sugihara laughs. “It’s hard to say.”

The practice of making sourdough is as ancient as bread itself. For 5,000 years or more, humans have mixed flour and water, waited for the mixture to ferment, and when it was good and sour and full of gas, used it as leavening to make dough rise. They found that they could propagate their leavening by saving a bit of unused dough to sow the seeds of foment in the next batch. No one knew then that these “seeds” were actually living microorganisms—it was Louis Pasteur, in the mid-1800s, who showed that fermentation was caused by microbes. That knowledge led to the commercial production of baker’s yeast, strains of Saccharomyces cerevisiae bred for speedy growth. Today baker’s yeast rules. It makes short work of pumping carbon dioxide into dough, and it always delivers. Still, the old, slow bread-making ways didn’t disappear. Sourdough, for example, not only survived in San Francisco—it has gained new respect from artisanal bakers and sourdough hobbyists.

“Here’s a sourdough bâtard from Artisan Bakers in Sonoma,” says Danielle Forestier, a French-trained master baker in Oakland, just across the bay from San Francisco. “I’m checking the package,” she reports over the phone. “It’s made of unbleached flour, water, and salt. Three ingredients, lots of taste, great texture.” Yet a typical supermarket white bread has more than 25 ingredients and additives and still tastes vapid.

The difference is those fermenting bugs. The baker’s yeast in supermarket bread creates a virtual monoculture of S. cerevisiae. The sourdough bâtard, on the other hand, is a product of natural fermentation involving wild yeasts and bacteria. Almost all the bacteria are lactobacilli, cousins of the bacteria that curdle milk into yogurt and cheese. “These lactobacilli outnumber yeasts in sourdough by as many as 100 to one,” Sugihara says. It’s the acids they make that give sourdough its tartness. Not only that, say European researchers, the bacteria also contribute carbon dioxide as well as aromatic compounds that infuse bread with flavor and delicious smells.

Keeping a sourdough culture alive requires good time management and something like affection. An ecosystem begins to form as flour mixes with water to make a starter dough. Enzymes in the flour split starches into sugars. There are swarms of yeasts and bacteria everywhere—in the flour, in the environment, and on the baker. They converge on the sugars “like a rabble,” says Jürgen-Michael Brümmer, former head of baking at the Federal Institute for Grain, Potato, and Lipid Research, in Detmold, Germany. Not to worry, he says: The bugs will sort themselves out, and the “bread friendly” ones will come out on top.

As lactobacilli convert sugars to lactic and acetic acid, the dough noticeably sours, going down to the pH of mayonnaise, around 3.8. Most microorganisms drop out of competition at this point, but yeasts that tolerate acid come into their own and convert sugars into carbon dioxide and ethanol. Gas bubbles and fruity smells signal that fermentation is under way. Served regular meals of flour and water—”refreshments” in sourdoughspeak—selected organisms will multiply day by day. By day six or so, the culture should teem with bugs and be ready to raise dough. Not all the culture is used, and the remainder is fed flour daily so it can live on to make bread another day. A well-fed culture can last years. “I call it microfarming,” says Rick Kirkby, at the Acme Bread Company in Berkeley.

In their landmark San Francisco sourdough studies, Sugihara and Kline showed how nicely yeasts and lactobacilli live together. The principal yeast they found now goes under the name Candida milleri, and the principal bacterium, a species never found in nature before, is called Lactobacillus sanfranciscensis. Unlike baker’s yeast, C. milleri is exceedingly tolerant of the acid that the bacterium produces. What’s more, C. milleri doesn’t digest maltose, one of the sugars derived from flour starch. This is unusual for a yeast, and lucky for the bacterium. L. sanfranciscensis, it turns out, can’t live without maltose. That tight, mutually helpful relationship may have allowed some San Francisco bakeries to keep their sourdoughs alive for more than 100 years.

Once scientists knew what to look for, they started finding L. sanfranciscensis in starter doughs in other countries—in French levains and German Sauerteigs, for instance, and in the dough for Italian panettone. Wherever it shows up, says Michael Gänzle, a microbiologist at the Technical University of Munich in Germany, it probably comes from bakers’ hands.

What to make of the claim, then, that San Francisco sourdough can’t be authentically made elsewhere? Will a San Francisco starter stay true to form in, say, New York? Many bakers contend the culture will lose its zip. “Local bugs join the party, and before long you’ve got Lactobacillus newyorkensis,” says Jeffrey Hamelman, director of the baking education center for King Arthur Flour in Vermont.

Perhaps. Cultures are dynamic. Mess with their living conditions— room temperature, mealtime, brand of flour offered—and they will change. But how much? An ongoing project in France may offer a clue. “Generally, we find the yeasts stay the same,” says Bernard Onno, a French microbiologist looking into the biodiversity and dynamics of sourdough. But in stable, established cultures, he says, “the lactobacilli vary—not the species but the ratios between the species in the dough.” Perhaps, then, if you transplant San Francisco sourdough to New York, you should expect some reshuffling within the bacterial inhabitants. The culture, however, isn’t always to blame for taste changes. “Fifty percent of taste comes from culture,” Onno says, but the other 50 percent comes from savoir faire—the baker’s craft.

“I think you can make San Francisco sourdough pretty much anywhere,” Sugihara says. “It’s such a self-protective system.” Now 82, he still consults for bakeries around the world. “They do a good job of sourdough in Japan,” he says, “but they mainly sell it to foreigners.” He has also persuaded one large Japanese bakery to perk up its white bread with a shot of sourdough. “They call the bread My Heart,” he says with a chuckle. “As in ‘I left my heart in San Francisco.'”

Source: Discover Magazine

Read also:

Lactobacillus sanfranciscensis : The Key to the Perfect Sourdough

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Growing Conditions

Lactobacillus sanfranciscensis has been cultured for many years through a procedure called “backslopping”– that is, the repetitive re-inoculation of a starter by adding flour and water, and never using the entire starter at any given time. This ensures that the bacteria are given plenty of nutrients to grow and multiply, prolonging the life of the starter. Over time, backslopping produces a steady ratio of certain bacteria, and thus a baker develops his or her own special flavor. Commericially-sold starters often include the basics, along with L. delbrueckii, fermentum, and plantarum.

Perfect function of L. sanfranciscensis relies on a balance of certain environmental conditions. Though bakers can specialize in certain techniques, additions, and temperatures, Ganzel et al (1998) revealed that L. sanfranciscensis itself does have an ideal environment to perform at its best, albeit broad (Figure B) . The group studied the contribution of ionic strength, pH, temperature, and metabolic end products (lactate, acetate, and ethanol) on the stability and metabolism of L. sanfranciscensis and its yeast counterpart C. milleri. They found that L. sanfranciscensis grew best between 30 and 37°C, whereas C. milleri responded well to temperatures below 26°C — this is consistent with the “baker’s rule” that temperatures between 20 to 26°C are preferable for yeast fermentation.

L. sanfranciscensis thrives best in a pH range of 3.9 to 6.7, and it is able to grow in up to 4% NaCl. It can tolerate over 160 mmol acetic acid and temperatures between 30°C and 37°C. By contrast, its symbiotic partner C. milleri thrives between 20°C and 27°C. It can handle a larger range of acidity, pH 3.5 to 7, and up to 8% NaCl. However, this yeast’s growth is completely inhibited by 150 mmol acetic acid. Thus, a process that encourages lactic acid production at higher temperatures and fermentation at lower temperatures must be considered in the creation of a proper sourdough. If acetic acid must be added for sourness, it should be done after fermentation to prevent yeast inhibition. Acetic acid may also be produced naturally by the addition of fructose or by increased aeration.

Although sourdoughs are normally prepared without salt, some bakers still opt to use some in their mix. Ganzel’s group found that adding salt to the dough inhibited lactic acid bacteria, including L. sanfranciscensis. This allowed for a faster growth rate of yeast, which were less sensitive to the addition. Thus, salt may be added to encourage fermentation and slow the rate of souring. The bacteria also had a specific range of acidity that encouraged growth. L. sanfranciscensis grew best at pH greater than 4.5, and did not grow well at all under pH 3.8. During the process of sourdough growth and fermentation, the pH drops significantly. Thus, lactic acid production occurs rapidly and stabilizes once pH drops to 3.8 and L. sanfranciscensis is unable to grow. This must be considered in the addition of acetic acid to some commercially-produced sourdoughs– the pH should match that of a sourdough acidified by L. sanfranciscensis at a pH of 3.8. Furthermore, since S. cerevisiae can tolerate lactic acid but not acetic acid, it is important that the addition of acetic acid to commercially-produced sourdoughs occurs after fermentation so that the bread has a chance to rise.

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Lactobacillus sanfranciscensis : The Key to the Perfect Sourdough . . . . .

Read also:

Lactic Acid Fermentation in Sourdough . . . . .

Video: Why Sourdough Bread is Healthy

Watch video at vimeo (1:50 minutes) . . . . .

Video: How to Make a Sourdough Starter Using Pineapple Juice Method

Watch video at You Tube (11:32 minutes) . . . . .

The History of Sourdough Bread

Vanessa Kimbell wrote . . . . . . . .

Bread is older than metal; even before the bronze age, our ancestors were eating and baking flat breads. There is evidence of neolithic grinding stones used to process grains, probably to make a flat bread; but the oldest bread yet found is a loaf discovered in Switzerland, dating from 3500 BCE. The use of leavening was discovered and recorded by the the Egyptians; there is some discussion about how this process happened, and the degree to which there was an overlap between brewing and bread-making, but obviously without a handy time machine it’s going to remain one a debating point among historians of ancient food. What is not in doubt is that the ancient Egyptians knew both the brewing of beer and the process of baking leavened bread with use of sourdough, as proved by wall paintings and analyses of desiccated bread loves and beer remains (Rothe et al., 1973; Samuel, 1996).

Wild yeast is used in cultures all over the world in food preparations that are so seeped in culture and history that they have been made long before any form of written words. The Sudanese, for example make kisra (fermented dough made with sorghum), The Ethiopians use wild yeast to make injera (teff), Mexicans make pool a fermented corn drink, Ghanaian kenkey and Nigerian use fermentation for their maize to make ogi, Indian idli breakfast cakes, made with rice, beans or chickpeas, and the Turkish make bona `( a ferment drink) generally with wheat, maize, sorghum, or millet and Nigerians ferment the cassava to make gari or fufu with.

Until the time of the development of commercial yeasts, all leavened bread was made using naturally occurring yeasts – i.e. all bread was sourdough, with it’s slower raise. Indeed, one of the reasons given for the importance of unleavened bread in the Jewish faith is that at the time of the exodus from Egypt, there wasn’t time to let the dough rise overnight.

From Egypt, bread-making also spread north to ancient Greece, where it was a luxury product first produced in the home by women, but later in bakeries; the Greeks had over 70 different types of bread, including both savoury and sweetened loaves, using a number of varieties of grain. The Romans learned the art of bread from the Greeks, making improvements in kneading and baking. The centrality of bread to the Roman diet is shown by Jevenal’s despair that all the population wanted was bread and circuses (panem et circenses). We have sourdough recipes from seventeenth century France using a starter which is fed and risen three times before adding to the dough. The French were obviously far more interested in good tasting bread over an easy life for the baker.

The introduction of commercial yeasts in the nineteenth century was to the detriment of sourdough breads, with speed and consistency of production winning. By 1910, Governmental bills preventing night work and restricting hours worked made more labour intensive production less sustainable, and in response, the bakers moved again towards faster raising breads, such as the baguette. It’s only since the nineteen eighties that there has been demand again for sourdoughs in the UK, to the extent that in 1993, regulations were issued defining what could be sold as a sourdough bread. In Germany, again, the use of sourdough was universal until brewers yeasts became common in the fourteen and fifteen hundreds. The overlap between brewing and baking was reflected in monasteries producing both bread and beer, using the heat of the oven to dry malted gain and the yeast to raise the bread. However, the big difference was that in Germany, sourdoughs continued to be used for rye breads, even as bakers’ yeasts became more popular for all other types.

While yeast is still used with rye flours, the sourdough is used to increase acidity, which prevents starches from degrading. This use in Germany is also seen in other countries with a strong rye bread tradition; Scandinavian countries and the Baltic states. Like France, the Germans have regulatory protection of what can be sold as sourdough.

The prospectors and explorers in the United States in the nineteenth century were referred to as sourdoughs as it was a practice to keep the mother leavening on your person, to make sure it didn’t freeze in the bitter winters. Personally I think that it was to get the yeast’s going, with the warmth so they would be more active and make better bread rather than as a freezing prevention measure. As a result, the bread in San Francisco was predominately sourdough, with bakeries such as the Boudin Bakery still baking today after having been founded in the mid nineteenth century.

Here in the UK, greater and earlier urbanisation, and the later invention of the Chorleywood process enabling the mass production of bread using softer English wheats moved baking away from small scale and artisanal production towards larger industrial methods. However, with the current triumph of television baking, and a re-invigoration of interest in the quality of the food we eat after the nadir of the post war period, interest in sourdoughs from smaller bakeries and home production is once again on the rise.

Source: The Sourdough School