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COMMENT BOOKS & ARTS CHEMISTRY A festive ferment Harold McGee surveys a seething array of microbially transformed treats — from beard beer and grasshopper sauce to extreme herring and armpit cheese. are is the holiday meal that does not thrive on sugars in nutrient-rich materi- by breaking down flavourless macromol- owe many of its pleasures to invis- als such as plant tissues and animal secre- ecules — starch, proteins and fats — into ible cooks with tongue-twisting tions. As these first exploiters multiply, their component sugars, amino acids and Rnames. Do you enjoy charcuterie and pick- they release a number of chemical weapons fatty acids. These building blocks have les? Bread with cultured butter? A drizzle of that suppress their competition, and so can flavours of their own and serve as precur- vinaigrette on this or that? A bit of cheese? delay or prevent the growth of microbes sors to a host of other small molecules Some chocolates? Wine, beer or cider? that spoil foods with disgusting or toxic that we can taste or smell. The food’s own Then raise a glass to Saccharomyces cer- by-products. The weapons include antimi- enzymes can do similar flavour-generating evisiae, Leuconostoc mesenteroides and crobial peptides, lactic and acetic acids, work from within in the extended time that their ilk, the fungi and bacteria and alcohols, all harmless to us in fermentation buys them. Eventually these that do the real work of turning moderation and some addic- changes go too far and the food becomes blandness into piquant delight. tively appealing. So shredded unappealing — effectively spoiled. That As a technology rather than cabbage and milk readily point is hard to define, and foods such as a metabolic mode, fermenta- turn sour, crushed fruits get Chinese stinky tofu and Swedish surström- tion is the managed micro- heady, and instead of the ming, or extreme herring, delight fans by bial transformation of raw putrid and inedible, we end flirting with it. plant and animal materials up with sauerkraut, clab- into foods that resist spoilage. bered milk and wine. MICROBIAL TEAMWORK Above all, it has been a method Today we easily preserve Food fermentations generally involve a of preserving the bounty of a har- raw foods simply by chilling community of various microbes growing vest or hunt for nourishment in leaner or freezing them, which slows all at the same time or in succession, but it is times. Peoples across the planet have applied biological activity. Yet fermented foods convenient to group them loosely by domi- it to nearly everything edible, from fruits, remain popular because they offer inten- nant organisms. By far the largest group of vegetables, meats and milks to animal hides sified, complex flavours. Stilton is more fermentations uses the lactic acid bacteria in the Sudan and fish heads in the Arctic. savoury than a spoonful of milk, chorizo or LAB, most of which associate with plants EMMANUEL LATTES/ALAMY SAUCE: SOY ONOZATO/AFLO/GETTY; TAKAO NATTO: KIMCHI: IMAGEMORE/GETTY; The most common food fermenta- tastier than steak tartare. The microbes and secrete pleasantly tart lactic acid. The OKSIX/SHUTTERSTOCK.COM; SALAMI: MARC WUCHNER/CORBIS; CHOCOLATE: CUCUMBER: WESTEND61/ALAMY; tions develop spontaneously, because the themselves generate complexity by turn- LAB produce an impressive array of our microbes responsible are ubiquitous and ing sugars into acids and alcohols, and favourite foods. Among them are yogurt, 372 | NATURE | VOL 504 | 19/26 DECEMBER 2013 © 2013 Macmillan Publishers Limited. All rights reserved BOOKS & ARTS COMMENT Delicacies in which fermentation plays a part include, left to right: pickled cucumber; salami; chocolate; Korean kimchi, or pickled cabbage; Japanese natto, or fermented soya beans; and soy sauce. cheese and cultured creams such as crème leavened breads, from Ethiopian injera to do-it-yourselfers fraiche; sauerkraut, Korean kimchi and other Italian panettone. have kept home pickled vegetables; dry-cured salamis and A third group is based on an Asian fermentation alive, similar sausages; Asian fish sauces; and the method for fermenting starchy foods, and in recent years rice–lentil batters for two South Indian and mainly the seeds of grains and legumes, foodies and artisans Sri Lankan specialities, the crêpe-like dosa which yeasts and LAB cannot utilize have been rediscovering and plump idli. directly. Some time before the second cen- its magic. Pickles and vinegars A second main group of food fermenta- tury bc, Chinese brewers domesticated are especially straightforward to tions stems from the yeasts, pre-eminently a species of Aspergillus mould to convert craft, and their variations and labels S. cerevisiae, which produce alcohols and the starch into fermentable sugars, at the seem to be growing logarithmically — as carbon dioxide from fruit juices and other same time generating its own distinctive is the baffling popularity of kombucha, sugar-rich liquids: hence wine and beer aromas. It is with the help of this Aspergil- sweetened tea fermented with what is and their distillates, brandies and whis- lus culture, called qu in China and koji in known among enthusiasts as a SCOBY. kies. If given the chance, certain bacteria Japan, that sake and other alcohols are made These symbiotic communities of bacteria will feed on alcohol, produce acetic acid, from rice. It is also how miso paste and soy and yeasts are solid cellulosic aggregates and turn wine into vinegar — or transform sauces including tamari are made from soya that have been found to include as many as bland and astringent cocoa beans in their beans and grains. Because Western brew- 20 microbial genera. In my experience, too fermented fruit pulp into the makings of ers have always prepared grains very dif- many cooks. I am partial to flavoured sau- richly flavoured chocolate. In thick doughs ferently, by ‘malting’ or partly germinating erkrauts (beets and ginger, Indian spices) and batters made from grain, which con- them to develop their own starch-digesting and local fresh natto, soya beans fermented tain enough sugar to support only limited enzymes, the koji fermentation has been lit- and made slimy by Bacillus subtilis, much yeast growth, the alcohols get cooked out tle known outside Asia until the past decade. superior to frozen imports. and it is the gas that Professional cooks have also caught NATURE.COM matters. It turns the MODERN REVIVAL the fermenting bug, with restaurants now For a Nature Podcast dense mass into a Today’s manufactured versions of fer- proudly offering their own distinctive pick- on fermented foods, light foam with a mented foods are often just approxi- les and cured meats. And a handful of pro- see: structure that is stabi- mated: many ‘pickles’ are just vegetables grammatically innovative restaurants have go.nature.com/elfmp6 lized by heat to make drenched in acids such as vinegar. But successfully adapted koji fermentation 19/26 DECEMBER 2013 | VOL 504 | NATURE | 373 © 2013 Macmillan Publishers Limited. All rights reserved COMMENT BOOKS & ARTS to Western ingredients. In New York City, the Momofuku restaurant group’s Culinary Lab has focused on miso- and tamari-like pastes and sauces made from non-soya bases such as cashews, pista- chios, chickpeas and spelt. Copenha- LIB. DIGITAL CALIFORNIA gen’s renowned Noma and the affiliated Nordic Food Lab have had good results with a yellow-pea ‘peaso’, a barley koji roasted to a chocolate brown and ver- sions of fish sauces made from grasshop- pers and from koji-treated beef. These experiments with fusion fer- mentation are probably just a taste of things to come. The James Beard Foun- dation, a New York-based “Provocation organization rather than of professional flavour has chefs, gave its motivated award for the experiments best reference with what book of 2013 might be called to Sandor Ellix personal Katz’s 500-page fermentation.” The Art of Fer- mentation (Chelsea Green Publishing), a jaw-dropping survey of possibilities from abará (Nigerian steamed or boiled fermented cowpeas) to zur (Polish sour rye porridge soup). Outside the restaurant world, provo- cation rather than flavour has motivated experiments with what might be called personal fermentation. After the Rogue Ales brewery in Newport, Oregon, failed to find beerworthy wild yeasts in its hop yard, it turned to a different local niche: a strain cultured from the brewmaster’s hair follicles now goes into the making of its speciality Beard Beer. And not- ing that we regularly devastate our own microbiome to suppress its produc- tion of the same odours that we enjoy in fermented foods, biologist Christina Agapakis and artist Sissel Tolaas have developed an exhibit to help us to bet- ter appreciate our unsanitized selves: cheeses made from milk inoculated with swabs of volunteers’ hands, feet, noses and armpits (see A. King Nature 503, 196; 2013). After a centuries-long stationary phase during which traditional food cul- tures slowly developed in isolation from each other, the world crock has been stirred and things are really bubbling. A forest of the Carboniferous period as depicted in The Fairy-Land of Science. Will new fermentations grace our future holiday spreads? Even the possibility is EDUCATION worth toasting. ■ Harold McGee is the author of McGee On Food & Cooking and Keys to Good Fairylands of science Cooking, both published by Hodder & Stoughton. Melanie Keene revisits two Victorian children’s science e-mail: [email protected] primers that harnessed interest in the supernatural. 374 | NATURE | VOL 504 | 19/26 DECEMBER 2013 © 2013 Macmillan Publishers Limited. All rights reserved.

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