Les microbes et champignons ont transformé le monde

This discussion explores the profound and often overlooked role of fungi, yeast, and bacteria—collectively referred to as "invasive living beings" or "cooks"—in shaping human food, culture, and even our biology. These microorganisms, though often associated with spoilage, are indispensable in creating a vast array of foods, from yogurt and cheese to wine and smoked ham. The process, broadly defined as putrefaction or decomposition of organic matter by these microbes, is fundamental to many culinary traditions. For instance, unpasteurized yogurt contains millions of live bacteria per gram, such as *Lactobacillus bulgaricus* and *Streptococcus thermophilus*, which convert milk sugars into more digestible lactic acid. Cheeses, with their longer and more complex fermentation processes, host diverse ecosystems of bacteria and fungi. Even industrial beer, though the "cooks" are eradicated before bottling, relies on billions of yeast cells during its preparation to transform sugars into ethanol. Despite these processes, most people don't associate these foods with putrefaction, yet the definition literally describes microbial decomposition. Since the dawn of humanity, our species has contended with the omnipresent threat of microorganisms deteriorating food. Historically, there have been three main strategies: eating food quickly before it spoils, slowing spoilage through methods like salting or smoking, or, most ingeniously, forming alliances with beneficial microbes to transform food into something edible, and often, succulent. Early humans, continually competing with visible predators and discreet decomposers, initially had cooking as their primary weapon against spoilage. However, accidental discoveries of beneficial rot occurred when food was left to spoil under specific conditions. While most uncontrolled spoilage results in unpalatable or even dangerous food—leading to parasitic infections, food poisoning from bacteria like *E. coli* or *Salmonella*, and general disgust—some instances led to extraordinary transformations. Beneficial molds, or ferments, contribute to the aroma of coffee and cocoa. Yeast ferments sugars into ethanol and causes bread dough to rise. Lactic bacteria in yogurt, sauerkraut, salami, and pickles convert sugars into lactic acid, creating an environment uninhabitable for pathogenic bacteria, thereby aiding preservation and enhancing flavor. The domestication of certain fruits, like grapes, for pressing and controlled rotting nearly 8,000 years ago facilitated the creation of wine. By learning to harness these beneficial decays, humanity shifted from competition to cooperation with microscopic organisms. This controlled rotting process, known as fermentation, involves adjusting temperature, salt, oxygen, and water, resulting in foods that are neither raw nor fully cooked, but constantly evolving. Microorganisms break down protein chains, tenderizing meat in sausages, breaking down lactose in milk, and predigesting gluten in bread, making foods more digestible. These ancient collaborations allowed humanity to preserve food, innovate flavors, and adapt to changing conditions. Intriguingly, evidence suggests that intentional fermentation predates agriculture and domestication. Traces of fermented grain beverages found in Israeli caves date back over 13,000 years, predating the invention of farming by 2,000 years. Similar findings indicate grape fermentation before vine domestication and cheese production before livestock raising. This suggests that the Neolithic revolutions might have been sparked by an "aperitif" and an alliance with microorganisms, enabling humans to become sedentary by extending the usability of wild resources. Fermentation also rendered otherwise toxic or indigestible foods palatable and nutritious. Wild grains and cabbage, potentially toxic in large quantities, become safer as bread or sauerkraut. Milk, difficult for adult Neolithic populations to digest, transformed into yogurt became a dietary staple. Olives, inedible fresh, require a salt water bath and bacterial action to soften and remove bitterness. Fermentation also preserves vital vitamins, like vitamin C in sauerkraut, which historically prevented scurvy among sailors. Furthermore, fermentation tenderizes food, making it easier to chew, and greatly increases its palatability. Today, fermentation is ubiquitous. Beer is the third most consumed beverage globally. Depending on the country, 5-40% of consumed food and drinks are fermented, with over 5,000 listed culinary preparations. Western Europe, particularly France, consumes significant amounts of fermented dairy products, leading to the daily ingestion of over 1,000 different species of microorganisms per person. These fermented creations are deeply intertwined with cultural identity, from French cheese and baguettes to German sauerkraut, Japanese soy sauce, and Vietnamese *nem chua*. Some fermented dishes, like Icelandic *hákarl* (fermented shark meat) or Swedish *surströmming* (fermented herring), are renowned for their pungent odors and challenging palatability to outsiders, demonstrating how cultural constructs can temper the universal human instinct of disgust towards putrefaction. This evolutionary legacy, designed to prevent the ingestion of dangerous foods, explains why strong flavors often require careful preparation or accompaniment. For millennia, humans practiced fermentation blindly, lacking understanding of the microscopic world. The invention of the microscope in the 17th century and Louis Pasteur's work in the 19th century finally revealed the role of microorganisms in fermentation, disproving earlier theories of spontaneous generation or mystical "ferments." Pasteur's 1865 patent for pasteurization, a process of eradicating natural microorganisms through heating and cooling, marked the advent of the modern food industry, transforming fermentation into a controlled scientific field. However, excessive selection and standardization can have consequences. The white rind of Camembert cheese, *Penicillium camemberti*, a fungus related to penicillin, prevents other molds and bacteria from growing. Historically, Camembert rinds varied in color, but since the 1950s, a single albino strain has been used, leading to genetic stagnation. This "cloning" prevents genetic mixing, causing the strain to "run out of steam," necessitating research into alternative solutions for its continued viability. Beyond the kitchen, microorganisms deeply influence our internal biology. Probiotics, ingested through fermented foods, become part of our microbiota—the vast community of bacteria in our digestive tract. This symbiotic ecosystem, weighing up to 2 kg in adults, not only aids digestion but also influences our immune system, reduces inflammation, and produces key neuroactive molecules like serotonin. Conversely, our mental activity impacts our microbiota, and strong emotions are often felt in the gut. Recent discoveries highlight the gut's "second brain"—approximately 500 million neurons—which collaborates with microorganisms to form a functional organ influencing mental health. Links between microbiota imbalances and anxiety, depression, and schizophrenia are being actively researched, with studies showing that transferring microbiota from depressed patients to healthy individuals can induce depression. The vagus nerve, connecting the gut to the brain's emotional centers, is a key area of study. Early signs of neurodegenerative diseases like Alzheimer's and Parkinson's can even manifest as gastric problems, underscoring the profound connection between our gut and central nervous system. Our digestive system, though not glamorous, is fascinating. The inside of our intestine, a tube formed during embryonic development, is technically "outside" our body. Its fractal, folded surface, equivalent to a tennis court in area when unrolled, provides a vast living space for our microbiota. To practice lacto-fermentation at home, choose vegetables like carrots, onions, pepper, garlic, and ginger. Use a clean, non-sterile jar with a seal that allows gas to escape. Prepare a brine by dissolving two tablespoons of salt in one liter of water. Rinse vegetables, pack them tightly into the jar, ensuring they are submerged in brine, leaving a few centimeters of air at the top. Close the jar and let it ferment at room temperature for over a week, then refrigerate for several weeks. The resulting "pickles" are a testament to the ancient art of controlled rot, reminding us that forgotten food items can be seen as invitations from microbes to explore new culinary possibilities.