In Search of the Perfect Loaf: A Home Baker's Odyssey (11 page)

While yeast may be spread by wasps, lactic acid bacteria are also found in many places: in the mouth, in the digestive tract, on fruits and vegetables, in feces, and in compost piles. But they are not floating around “in the air,” as I’ve also heard so often from bakers, and which I believed for years. Neither yeast nor bacteria survive long in open air, which is why it’s unlikely that a traipsing bacteria or yeast cell will blow into your kitchen and inoculate your infant batch of sourdough starter. These organisms need to travel on some kind of agent—saliva, juice, insects, skin, fruit—but eventually they can become established in the microclimate of a bakery, or even brewery, and then, yes, they can be found in the air. But the science is clear: they aren’t in your kitchen at the outset.

Scientists are just starting to tease out
the origins of these microscopic cells, and they are finding strong evidence that they originate in the bowels of various animals. From there, they migrate into flour or dough. One study found that
Lactobacillus reuteri
in a rye sourdough matched a strain found in the entrails of rodents. Another species in wheat sourdough was identical to one found in the human intestine. Still other strains mirrored those found in the vagina. (This gives new context to the role of the seventeenth-century French
geindre
, mounting the dough in a fetid basement baking room as he kneaded the mass, sweating and sputtering and inoculating the substance with his various effusions. Maybe this made for a lively fermentation.)
But lactobacilli are far more prevalent
in the viscera of pigs, mice, chickens, and rats than in humans. Michael Gänzle, an authority on the science of sourdough at the University of Alberta in Canada, who coauthored the groundbreaking study on the intestinal origin of lactobacilli, told me that rodents likely infect the grain at the farm, mill, or bakery.
Or they might arise
, as one paper delicately put it, from “fecal contamination in the sourdough production environment.”

Insects may also play a key role
. In a South African study, thirty species of lactic acid bacteria were isolated from the guts of fruit flies, including those bacteria commonly found in sourdough starters. When I first heard about this study, it suddenly hit me that this may be the reason that fruit flies congregate above the starter bubbling away on my kitchen counter. They love the stuff. I actually created a fruit fly trap by putting ripe sourdough in a plastic container, covering it with plastic wrap and punching holes in the top. The fruit flies dive in like kamikazes and then perish. The reason:
fruit flies lay their eggs
when they smell ethanol from a fermented substance, for it signals that their larvae will have access to a complete diet of sugars, high-protein yeast, and even alcohol, for survival. Maybe they were the source of the bacteria in my sourdough. But when I put it to Gänzle, he told me that this hasn’t been studied enough to get a definitive answer.

Sadly, these microbiologists destroyed a myth that I and so many bakers had accepted for so long: the idea that sourdough reflects a particular region.
Lactobacillus sanfranciscensis
, first discovered in 1971, for example, was long thought to be unique to San Francisco and gave the city’s sourdough bread its tangy flavor. It’s a nice story but the species has now been found globally and is among the most prevalent type of
Lactobacillus
in sourdough. Interestingly, it hasn’t yet been found anywhere else in nature, aside from sourdough and the guts of South African fruit flies.

Ultimately, the bacteria that do take up residence in sourdough reflect the ecology of the substance. This, in turn, is determined by the amount of water in the starter, the frequency of refreshment, the ambient temperature, the type of flour, and how much starter is used to rebuild a new batch. Change these factors and the microbiota within the mix might change as well. Feed the leaven at a temperature between, say, 68˚F and 80˚F (20˚C to 27˚C), once or twice daily, and odds are about one in four that you will eventually get
Lactobacillus sanfranciscensis
in your starter. But if, like industrial makers of sourdough, you keep the temperature of your leaven at 100˚F (38˚C) and feed it every few days, far more
acid-tolerant bacteria
will arrive, such as
Lactobacillus reuteri
.

I’ve learned to manipulate sourdoughs to work with various flours, and I now believe that the starter has more influence on the flavor of the bread than the flour itself. That said, the type of flour used to feed the starter will affect the bread’s taste as well. If you mix the sourdough with rye, it will taste more earthy and less grassy than wheat. If you mix the starter so it resembles a stiff ball, and keep it at a rather cool temperature of around 67˚F (19˚C), it will develop a tangy edge. That’s because the bacteria producing the sour-tasting acetic acid will dominate in a cooler, stiffer culture. Produce a leaven that resembles pancake batter and ferment it at 80˚F (27˚C) and you will instead favor the production of lactic acid, which resembles the rounder notes of yogurt. The most extreme example I’ve encountered is a
German Detmolder rye sourdough
described in Jeffrey Hamelman’s book
Bread
. The sourdough is fermented and refreshed at three different temperatures for varied lengths of time to influence the taste of the final loaf. There’s no need to go to these extremes—you’d need a temperature-controlled cabinet to achieve such Prussian precision in making a sourdough culture—but it does help illuminate what a bit of flour, water, organisms, and fermentation can achieve. Whatever the method, if the starter is fed regularly and maintained at a consistent temperature, the microbes will likely remain consistent, too.
That is why scientists have found
highly stable bacterial cultures when looking at bakeries’ sourdough starters.

But the biota in my sourdough will probably not match yours, even if I gave you a bit of my starter to begin with and you lived down the block.
So far, more than fifty-five species
of
Lactobacillus
have been identified in sourdoughs, yet a study of
nineteen Italian sourdough cultures
showed that each was unique—that is, none shared the precise same mix of organisms. Another study found that
cultures can even change
when moved from one setting to another. Of course, this tends to undermine the romantic notion of keeping a culture alive for years, decades, even centuries, and passing it on, so that it spreads out, multiplies, but maintains its original essence. Bakers have relied on sourdough since antiquity and it’s taken on mythic status. “Here, take some of my culture that has been kept alive for 250 years,” someone might say, which is a lovely but meaningless gesture. A culture can be nurtured this way, but unless all the conditions mirror the original, it is unlikely to harbor the same combination of yeast and bacteria. Nature loves diversity, whether we like it or not.

Several years ago, I had the chance to meet New York baker Jim Lahey (the guy behind no-knead bread). I coveted the loaves he made at Sullivan Street Bakery and their light, airy quality. I would just rip off a piece and chew it as I walked down the street. The bread had an unforgettable texture and taste. When I met him, a few years after I first discovered the bread, I brought along a loaf for him to critique. This was in the days when my own starter, I realize, was rather weak and the loaves were dense, but he complimented me. When we walked through his baking room, I asked if he would share some of his sourdough—a request I’ve made to a number of bakers over the years. Like all the rest, he didn’t hesitate. He reached into a bin and pulled out a golf-ball-size piece of sourdough, putting it into a pint container. He mentioned that it had originally come from Italy.

I took it home on the train and dutifully kept the starter alive for a couple of years, thinking that I was tapping into some secret colony of Italian microorganisms. I found, however, that it didn’t perform any differently than other sourdough cultures I had made. I now realize that within a couple of weeks it had probably adapted to my kitchen microclimate and feeding schedule, picking up whatever wild yeast and lactic acid bacteria were already in residence because I baked frequently with sourdough. They probably beat out the original Italian relatives in the starter, or more likely, the pushy New Yorkers who had already displaced the Italians. The starter wasn’t really the point, though, when it came to the light, airy quality I coveted in his breads. As I later learned (practice, practice), his bread had more to do with fermentation (using commercial yeast), hydration (a lot of water), and fabrication (gentle handling of a very viscous dough) than it did with the starter. Or, at least, that’s what I concluded when I tried to reverse-engineer the bread.

So let’s toss aside the myths about sourdough starters: that only San Francisco sourdough can be made in San Francisco; that you can nurture a culture from somewhere else that dates back two hundred years without changing it; that if your two-hundred-year-old starter dies, you will never get it back (there’s a good chance the organisms that repopulate the new starter will turn out to be the same as before, all else being equal). Or that all the sourdough methods I tried worked because they were good methods (they probably were, but they might also have worked because wild yeast and bacteria were probably thriving in my kitchen since I bake with sourdough regularly). Starters are actually hyperlocal, with an ecology influenced by the hand of the baker, this farmer of microorganisms, and his particular feeding regime. And isn’t that ultimately what local is? Making decisions within the confines of your bioregion, even if that happens to be a slurry of flour and water sitting on your kitchen counter?

In the early days of baking, however, I understood none of this. I just knew that if I took a quarter cup of starter out of the refrigerator and mixed it with warm water and flour, it would rise after eight hours or so. If I hadn’t baked with the substance for a week or more, I’d feed it twice, or even three times, before I mixed the dough. By the end of that feeding schedule, I could tell the difference. The starter was more lively, it bubbled and made the difference between a lofty loaf and a dense one. I learned these lessons only by practice and observation, and in doing so, I generally veered away from what I was reading in books. In the end, the process led me to my house loaf: a mixture of white flour, whole wheat, and rye that might be called
pain de campagne
and has had a presence on our table for more than a decade.

It’s not original, but it was clearly my bread, with a taste and texture that arises from those organisms that I’ve learned to cultivate so well. But this loaf had a rich lineage, a long line of influence, not only from the books of people like Nancy Silverton and Dan Leader, who have built businesses on the backs of their humble sourdough starters, but from a movement of artisan bakers. At some point, I knew I had to visit them and learn where my bread came from.

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