Tangy sour­dough’s se­cret in­gre­di­ent?

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It’s easy to get a rise out of a lo­cal TV news crew. Es­pe­cially in a slo-mo state cap­i­tal like Cal­i­for­nia’s. So it was on Septem­ber 6, 2007, when KCRA’s LiveCopter 3 hov­ered over a Sacra­mento park­ing lot, at 8:23 a.m., beam­ing images of a slow-mov­ing red van, tailed by a black-and-white po­lice cruiser. As soon as the van pulled over, a man in a white baker’s cap popped out. In­stead of mak­ing a run for it, which is how you ex­pect these things to play out, he la­bored up to a reporter’s mi­cro­phone, arms weighed down by bread dough. “It’s about 40 pounds,” he said. A crowd of by­standers cheered.

The Boudin Bak­ery in San Fran­cisco, the city’s old­est and one of the best-known pur­vey­ors of its fa­mous sour­dough bread, was de­liv­er­ing a key piece of its his­tory to its new­est out­post. Since 1849, the bak­ery has re­lied on a bac­te­ri­aand-yeast-rich “starter”—a small amount of dough that bak­ers reg­u­larly “feed” by adding flour and wa­ter—to breed the liv­ing or­gan­isms that make the bread rise and give sour­dough its tang. Prop­erly cared for, a starter can birth bil­lions of chewy loaves across decades and even cen­turies.

The pre­dom­i­nant bac­te­ria in sour­dough is called Lac­to­bacil­lus san­fran­cis­cen­sis. It’s a species that pro­duces lac­tic and acetic acids, which give sour­dough its dis­tinc­tive and nom­i­nal fla­vor. For decades, food­ies be­lieved, as did Boudin’s bak­ers and oth­ers, that the city’s fog and tem­per­ate cli­mate helped foster these micro­organ­isms. As it turns out, they may come from in­sects.

In July 2017, baker Ian Lowe re­sponded to a bit of news that re­vealed an un­usual con­nec­tion be­tween bugs and bread, and that had at­tracted his com­mu­nity of sour­dough devo­tees: “It’s time bug shit got its due,” he told his more than 28,000 In­sta­gram fol­low­ers.

Each year, some 50 or so bak­ers from around the world visit Lowe at his Apiece bak­ery in Launce­s­ton, Tas­ma­nia, to study his sour­dough-bak­ing tech­niques. Lowe—who has read ex­ten­sively in plant breed­ing, mi­cro­bi­ol­ogy, milling sci­ence, and oven ther­mo­dy­nam­ics, and taught him­self ba­sic chem­istry, bio­chem­istry, and molec­u­lar bi­ol­ogy, to bet­ter un­der­stand the mi­cro­biome of his fa­vorite food—posts his ex­act­ing recipes in a pub­lic Drop­box file for all to share.

That week in July, Lowe had read a newly pub­lished mi­cro­bi­ol­ogy pa­per that showed, more than 40 years af­ter sci­en­tists iden­ti­fied L. san­fran­cis­cen­sis in sour­dough, that the bac­te­ria live in­side in­sects that in­habit wheat fields and grain store­houses. It makes sense that bac­te­ria that can thrive in the fer­ment­ing plant ma­te­rial “would be some­thing that’s part of the ecol­ogy of the grain,” Lowe says. They must all share re­gional ori­gins and thrive in a tem­per­ate range—be­tween 65 and 80 de­grees Fahren­heit. Al­though as a non­sci­en­tist Lowe had no way to prove it, his stud­ies and his life’s work had led him to rea­son that the in­sects’ guts must be per­fect vec­tors for the nec­es­sary micro­organ­isms of fer­men­ta­tion.

These in­sects have been eat­ing the grain hu­mans put aside for mil­len­nia. Now it seems they may have played a culi­nary role in feed­ing our an­ces­tors. Thou­sands of years ago, Ne­olithic cul­tures planted fields of wild wheat, such as einkorn and em­mer, then crushed their grains and mixed them into wa­ter to make a por­ridge. Some baked it on hot stones as flat­bread. No one knows where it hap­pened, but around 6,000 years ago, a care­less cook must have left por­ridge out

overnight and no­ticed the next day that it had bub­bled up. Fer­men­ta­tion! Stuck in an oven, it plumped and pro­duced what we now know as chewy, aro­matic, and life-sus­tain­ing bread.

HO KNOWS IF THIS UR-BREAD was sour­dough, but even­tu­ally that genus of daily carb spread through the Mid­dle East and Europe, be­com­ing a nu­tri­tious sta­ple for much of Western civ­i­liza­tion. The process was sim­ple. Start with flour and wa­ter. Let it fer­ment for a few days, reg­u­larly adding more flour and wa­ter and keep­ing the mix­ture warm enough to al­low the wild yeasts and lac­to­bacilli on the grain to do their job—bub­bling with gas and thick­en­ing. Then add a chunk of this starter to a dough of more flour and wa­ter, let it sit for sev­eral hours, then pop it in the oven and bake to good­ness.

No one could ac­tu­ally ac­count for the mys­te­ri­ous in­ter­nal re­ac­tions of starter un­til the mid-19th cen­tury, when Louis Pas­teur de­ter­mined that yeast was a mi­cro­scopic liv­ing chemist that turned sugar into al­co­hol and gas. That soon led to the in­ven­tion of con­cen­trated baker’s yeast, which trimmed the la­bor-in­ten­sive bread-mak­ing process from days to mere hours. It also yielded a mono­cul­ture fer­men­ta­tion of dough, with less bio­chem­i­cal and nu­tri­ent diver­sity. That ush­ered in the fla­vor­less, mass-pro­duced prod­uct that sits on su­per­mar­ket shelves to­day, full of dozens of mul­ti­syl­labic thick­en­ers and ad­di­tives. In Europe, Old World bread-mak­ing prac­tices, which re­quire spe­cial­ized skill and pa­tience, en­dured even amid the on­slaught of the quick-fix, pack­aged stuff. But start­ing around the 1990s, the ar­ti­sanal move­ment in the United States saw chefs re­ject­ing baker’s yeast and com­menc­ing an ob­ses­sion with sour­dough and the live starter re­quired to make it.

Even so, among bak­ers and re­searchers who study food, “the ori­gin of sour­dough micro­organ­isms is some­what of a mys­tery,” says Anne Mad­den, a post­doc­toral re­searcher at North Carolina State Univer­sity who calls her­self a mi­cro­bial strate­gist. Mad­den and her su­per­vi­sor, ecol­o­gist Rob Dunn, are part of a global yet small club of re­searchers try­ing to solve the mys­tery. Their Sour­dough Project has col­lected more than 550 spec­i­mens of live starter from around the world—some of them handed down through gen­er­a­tions—in an at­tempt to cat­a­log the micro­organ­isms that pop­u­late them.

The first to try to crack the mys­tery of San Fran­cisco sour­dough were T. Frank Sugi­hara and Leo Kline, a pair of mi­cro­bi­ol­o­gists work­ing in the Bay Area in the 1970s for the U.S. De­part­ment of Agri­cul­ture. At the time, bak­ers swore that no one in the coun­try could re­pro­duce the tangy food more than 50 miles away from the city, and that starters trans­planted to other places would rise but usu­ally lose their sour fla­vor. In their land­mark stud­ies, the pair found that yeast and a bac­te­ria that would later be dubbed Lac­to­bacil­lus san­fran­cis­cen­sis, af­ter the city known for sour­dough, worked to­gether to make dough rise and taste good.

A sour­dough starter is an ecol­ogy primed for these two com­ple­men­tary play­ers, with lac­to­bacilli out­num­ber­ing yeast 100 to 1. En­zymes in­side the flour break starch into the malt sugar known as mal­tose. But sour­dough yeast can­not me­tab­o­lize mal­tose. It snacks on other sug­ars in the dough in­stead, cut­ting them down to make sim­pler vari­ants such as fruc­tose and glu­cose, and port­ing them into the fer­men­ta­tion path­ways that ex­tract en­ergy. When they’re done, what’s left over is a tiny scrap of ethanol and the car­bon diox­ide that puts rise in your dough. Mean­while, lac­to­bacilli chow down on the mal­tose and re­lease fla­vor­ful acids as waste.

In sour­dough, yeast and lac­to­bacilli work as a team. But no­body knew where lac­to­bacilli came from. Bak­ers didn’t add the stuff, and other foods that used the same in­gre­di­ents lacked its dis­tinc­tive fla­vor el­e­ment.

Sci­en­tists be­gan look­ing for and find­ing it in starter doughs in Ger­many, France, and Italy—all places with a rich sour­dough his­tory. Many peo­ple, in­clud­ing mi­cro­bi­ol­o­gists, be­lieved it came from bak­ers’ hands. But Clau­dia Pi­cozzi, an as­sis­tant pro­fes­sor at the Univer­sity of Mi­lan, was work­ing on an al­ter­na­tive idea.

P TO THAT POINT, SAYS PI­COZZI, “no one was able to de­tect the micro­organ­isms in the grain or flours” used for mak­ing sour­dough. Then one of her col­leagues thought of in­sects. Or, rather, their guts. “Sev­eral lac­tic-acid bac­te­ria and yeasts have in­testi­nal ori­gin,” says Pi­cozzi, ex­plain­ing her think­ing. “And since many in­sects live on ce­real grains and in­fest flours for baked prod­ucts, we thought we prob­a­bly could trace the ori­gin.”

So she and some col­leagues set about scoop­ing the poop of sev­eral species (among them the charm­ingly named con­fused flour bee­tle) that in­fest grain and flour stores. Af­ter se­quenc­ing the DNA in­side the pests’ poop, they pub­lished their find­ings in the Jour­nal of Ap­plied Mi­cro­bi­ol­ogy with the help­ful ti­tle: “In­sect frass in stored ce­real prod­ucts as a po­ten­tial source of Lac­to­bacil­lus san­fran­cis­cen­sis for sour­dough ecosys­tem.” It turns out, there’s lots of bac­te­ria in bug poo. The re­searchers found more than 130 species. Lac­to­bacilli made up only 0.36 per­cent of that to­tal. But the most com­mon was Lac­to­bacil­lus san­fran­cis­cen­sis.

So why did a mi­nor player in the in­sect gut dom­i­nate in dough? One rea­son for its suc­cess, says Fran­cisco Migoya, head chef at Mod­ernist Cui­sine, the sci­ence-of-cook­ing lab in Belle­vue, Wash­ing­ton, is eco­log­i­cal. “It is ba­si­cally cre­at­ing a poi­son, so the other bac­te­ria are go­ing to die,” says Migoya, who co-au­thored the five-vol­ume Mod­ernist Bread: The Art and Sci­ence. By chang­ing the en­vi­ron­ment it lives in, Lac­to­bacil­lus san­fran­cis­cen­sis out­com­petes its neigh­bors and, as a re­sult, it in­flu­ences sour­dough’s fla­vor.

Stud­ies like Pi­cozzi’s don’t just solve nerdy bak­ing trivia ques­tions. They also of­fer real-world ap­pli­ca­tions to both ar­ti­sanal and in­dus­trial bread-mak­ing. “Such knowl­edge can help us de­sign breads with bet­ter fla­vors and ones that are health­ier for us,” says NCSU mi­cro­bi­ol­o­gist Anne Mad­den. One of her projects ex­am­ines the mi­crobes that part­ner with in­sects such as wasps and bum­ble­bees. She and her col­leagues have found new yeasts on these winged field in­hab­i­tants that she hopes “can make breads with use­ful traits.”

Mad­den’s men­tor, Rob Dunn, who runs an ecol­ogy lab at the univer­sity, says bugs are likely not the whole story. Fur­ther DNA analy­ses might turn up other cooks in the mi­cro­bial kitchen. “The story has many pieces,” he says, “one of which might be in­sects, but so too the body of the baker, the air of the bak­ery, the grain in the field, the mi­crobes in the soil.”

So, as we learn to con­trol the vari­able, we learn to con­trol the prod­uct. The more we master the in­gre­di­ents, the more de­lib­er­ate we can be in cre­at­ing new kinds of baked goods. But un­til we know more, be sure to thank your tiny chefs: the bugs.

It turns out there’s plenty of bac­te­ria in bug poo— the same bac­te­ria that gives sour­dough bread its tang.

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