The Noma Guide to Fermentation

1.

Primer

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What Is Fermentation?

What Makes Fermentation Delicious?

Setting the Table for Microbes

Wild Fermentation

Backslopping

Cleanliness, Pathogens, and Safety

Potential of Hydrogen (pH)

Salt and Baker's Percentages

Building a Fermentation Chamber

Thinking Outside the Kraut

Substituting Store-Bought Ferments

Weights and Measures

What Is Fermentation?

Before we dive into the practical ins and outs of fermentation, let's first clearly define what it is.

At the most basic level, fermentation is the transformation of food by microorganisms—whether bacteria, yeasts, or mold. To be slightly more specific, it is the transformation of food through enzymes produced by those microorganisms. And finally, in the strictest scientific definition, fermentation is the process by which a microorganism converts sugar into another substance in the absence of oxygen.

The word fermentation comes from the Latin word fervere, meaning "to boil." The ancient Romans, upon seeing vats of grapes spontaneously bubble and transform into wine, described the process using the closest analogue they could think of. And while those bubbling vats of grapes had nothing to do with boiling, they were true ferments in the scientific sense, as yeast-produced enzymes transformed the sugars in the grapes into alcohol.

However, not all the processes we consider to be fermentation fit neatly into tidy definitions of it. For instance, while koji is faithful to the definition, Noma's garums are not. In koji, the mold Aspergillus oryzae penetrates grains of rice or barley and produces enzymes that convert the grain's starches into simple sugars and other metabolites. This is what's known as a primary fermentation process. The garums in this book, on the other hand, are the product of a secondary fermentation process. To produce garum, we mix koji with animal proteins in order to take advantage of the enzymes produced during the primary fermentation process.

We don't differentiate between primary and secondary fermentation processes in this book, but you may find it helpful to have these definitions under your belt as you find your way with fermentation.

What Makes Fermentation Delicious?

Taste is a function of the human body, and to understand what tastes good to us, we have to understand its role in our evolutionary history. All our senses serve to aid in our survival. Our senses of taste and smell have been shaped over hundreds of millions of years to incentivize us to eat foods that are beneficial to our bodies. Our tongues and olfactory system are unbelievably complicated organs that take in chemical cues from the world around us and transmit that information to our brains. Taste lets us know that a ripe piece of fruit is sweet and thus full of calorie-rich sugar, or that a plant's stalk is bitter and potentially poisonous. We are born with aversions to certain flavors (a sense that becomes reinforced by experience), leading us to gag at the stench of rotting flesh decaying at the hands of pathogenic bacteria, while we register the scent of meat roasting over fire as mouthwateringly delicious, because it indicates to our brains that we're about to eat something rich in proteins.

There are numerous biological processes at work in any given fermentation, but the ones that matter most to us from a taste perspective are those that break down large chains of molecules into their constituent parts. The starches in foods like rice, barley, peas, and bread are actually long chains of linked molecules of glucose, a simple sugar. Proteins, which can be found in large supply in soybeans and meat, are constructed in a similar fashion from lengthy, winding chains of amino acids—small organic molecules essential to all aspects of life on earth. One of those amino acids, glutamic acid, registers on our taste receptors as umami—the elusive, crave-able quality that connects foods like mushrooms, tomatoes, cheese, meat, and soy sauce.

So what makes fermentation so good? On their own, starch and protein molecules are too large for our bodies to register as sweet or umami-rich. However, once broken down into simple sugars and free amino acids through fermentation, foods become more obviously delicious. Koji made from rice has an intense sweetness that plain cooked rice doesn't. Raw beef left to ferment into garum has a savoriness that speaks to us on a primitive level.

Simply put, the microbes responsible for fermentation transform more complicated foodstuffs into the raw material your body needs, rendering them more easily digestible, nutritious, and delicious. Our affection for the tastes those microbes produce has allowed them to evolve and stay in our company. Humans have been fermenting for so long that many of the microscopic agents responsible can be considered domesticated, just like household cats or dogs. But while pets can stare longingly at you if they're hungry or cold, microbes are a bit trickier to read. It's a mutually beneficial relationship, but one that needs a bit of work to keep everyone happy. That's the job of the fermenter.

There's a thin line between rot and fermentation, and that line might best be understood as an actual line, like the kind you'd find outside a nightclub. Rot is a club where everyone gets in: bacteria and fungi, safe or unsafe, flavor enhancing or destructive. When you ferment something, you're taking on the role of a bouncer, keeping out unwanted microbes and letting in the ones that are going to make the party pop.

You have several tools at your disposal in trying to encourage certain microbes or deter others. Some organisms are more tolerant of acidity than others. Likewise with oxygen, heat, and salinity. If you're familiar with what your preferred microbe needs to function, you can wield these factors to your benefit. Each chapter in this book will go into great detail about the conditions you need to create successful fermentation, but for starters, here's an overview of the players that will be working for us.

Bacteria

Among the earliest forms of life, bacteria are single-celled organisms that are present in uncountable quantities in nearly every corner of the globe. Only a fraction are known to science. There are malignant bacteria that can produce toxins capable of killing much larger organisms. At the same time, there are billions of beneficial bacteria living on and inside of us. At the end of the day, the majority of them are harmless to us.

LAB are rod- and sphere-shaped bacteria that are present in abundance on the skins of fruits, vegetables, and humans. We use them for their ability to convert sugar into lactic acid, giving pickles, kimchi, and other lacto-fermented products their characteristic sourness. Because they produce lactic acid, they are able to tolerate low-pH environments. They are also halo-tolerant (salt-tolerant) and anaerobic, meaning they thrive in the absence of oxygen.

Like LAB, AAB are readily abundant rod-shaped bacteria, ever present on the surface of many foods. They generate the sharp sourness of vinegar and kombucha by converting alcohol to acetic acid. We often use them in conjunction with yeasts that first convert sugars into alcohol. They can tolerate the acidic environments they create, and require oxygen to create acetic acid, thus classifying them as aerobic bacteria.

Fungi

Fungi encompass a huge swath of life on earth, from single-celled yeasts to molds to gigantic puffball mushrooms. Multicellular, filamentous fungi like mushrooms and molds grow by gathering nutrients through tendril-like hyphae that together form a web-like system known as a mycelium, similar to the roots of a plant. They secrete enzymes through their mycelium, effectively digesting the food in their surroundings, then absorbing the nutrients from their environment.

An extremely handy species of yeast, Saccharomyces cerevisiae is responsible for three of humanity's most important culinary pillars: bread, beer, and wine. Bountiful in the natural world, as demonstrated by producers of spontaneously fermented bread and wine, S. cerevisiae makes a living converting sugars into alcohol. It breaks down glucose to harness the chemical energy needed for its life processes, while producing carbon dioxide and ethanol as by-products. Different strains or subspecies are harnessed for their particular qualities, which can lead to wide variations in flavor. For instance, the strain of S. cerevisiae that is used in bread baking isn't desirable for producing beer or wine. Yeast can survive and multiply in the presence of oxygen, but alcohol fermentation takes place anaerobically. Saccharomyces dies at temperatures in excess of 60°C/140°F.

A genus of long, cylindrical yeast, Brettanomyces is used in the production of beers with sour qualities because of its ability to produce acetic acid as a metabolite. Brettanomyces also occurs naturally on the skins of fruits, and can be purchased readily as "saison yeast." It can survive in oxygen, but produces ethanol anaerobically. Like other yeasts, it cannot survive temperatures above 60°C/140°F.

Perhaps the most important microbe in this book, A. oryzae (pronounced oh-RAI-zee) is the sporulating mold also known as koji. It's been bred for hundreds of years to grow extremely quickly in hot and humid environments when given access to the plentiful starches in products like cooked rice or barley. (Generally speaking, 30°C/86°F and 70% to 80% humidity are ideal for Aspergillus; temperatures above 42°C/108°F will kill it.) Koji secretes the enzymes protease, amylase, and a small amount of lipase, which break down proteins, starches, and fats, respectively. We harness these enzymes in the production of our misos, shoyus, and garums.

A relative of Aspergillus oryzae, Aspergillus luchuensis (pronounced loo-CHOO-en-sis) metabolizes starches and proteins and produces citric acid as a by-product. It's traditionally used to brew the bases of Asian spirits like Korean shochu and Japanese awamori, as the distillation of the alcohol leaves the citric acid behind. Though it's a lesser-known species, it's extremely delicious.

Enzymes

Enzymes are not microbes—they aren't even alive—but rather biological catalysts that facilitate chemical transformations within organisms or organic matter. You can generally identify them by the suffix -ase, as in protease (an enzyme that breaks down proteins) and amylase (from the Latin word amylum, meaning "starch," which breaks down exactly that). They are a class of proteins built through evolution to serve specific but different functions. Exactly how they work is rather complicated, but you can think of the ones featured in this book as a cross between keys and scissors. They're keys in the sense that they are tailored to fit specific locks, acting on one organic molecule while leaving others alone; and they're scissors in that they can cut ribbons into shorter lengths. Generally speaking, enzymes work most efficiently in warm, fluid environments, but if heated too high, they can be "cooked" to a point where they no longer function.

Wild Fermentation

The ferments we undertake at Noma all depend to varying degrees on wild fermentation. That is to say, we create environ-ments that are conducive to the growth of naturally occurring beneficial microbes, and detrimental to malevolent ones. With our lacto-ferments, for instance, we depend entirely on a wide set of lactic acid bacteria in the environment—on the fruit or vegetables we're fermenting, on our hands, floating in the air—to turn sugar into lactic acid and other flavorful metabolites. By allowing nature to do its thing, we get layers of nuance and complexity in our ferments that wouldn't be possible if we dictated exactly which microbes were allowed to work. Wild fermentation is a non-inoculated and often very diverse fermentation. Simply put, it's how fermentation was first performed, and it's still tried and true.

For our kombuchas, vinegars, and koji, we do introduce bacteria, yeast, or fungus into the equation in order to get the results we're looking for, but we still allow and encourage wild fermentation. The same goes for especially large batches of lacto-fermented products. For instance, when we're fermenting hundreds of kilos of asparagus at a time, we add powdered lactic acid bacteria (LAB) to the brine. If for some reason the naturally occurring LAB had trouble getting started, we'd be exposed to the risk of some other malignant microbe taking hold. A boost in the LAB population is a nice bit of insurance against losing all that product when you're working on a large scale.

Backslopping

Backslopping is a vital technique in prepping microbial environments for fermentation and will come up numerous times in this book, especially in the production of kombucha and vinegar. The idea is basically to give the substance you intend to ferment a boost of beneficial microbes by adding a dose from a previous batch of that same ferment.

By pouring a healthy amount of, say, perry vinegar into a jar of fresh perry, we both lower the pH of the solution and add a healthy shot of acetic acid bacteria (AAB). Lowering the pH (acidifying) has the effect of slowing or stopping any unwanted microbes that aren't acid-tolerant from acting on the perry, and ensures that there's a healthy population of AAB to ferment the perry into perry vinegar. Backslopping stacks the deck in favor of the microbes we want to succeed.

Of course, if this is your first time making one of the ferments in the book, you won't necessarily have a previous batch to use for backslop. In that case, you'll have to find a similar substitute. For our vinegars, we suggest unpasteurized apple cider vinegar as a replacement. For our kombuchas, you can use a similarly flavored unpasteurized kombucha or the liquid that your SCOBY (the "mother" culture of yeast and bacteria that produces kombucha; see cooperative frementation) comes packaged in. The downside is that you're going to dilute the pure flavor of the vinegar or kombucha you're making. That's fine, though, as it gives you a perfect reason to make the same vinegar or kombucha again—this time using a portion of your first batch as backslop.

Cleanliness, Pathogens, and Safety

Cleanliness is something we take very seriously in the kitchen, out of both pride for our workplace and respect for our colleagues. However, a clean and sanitary workplace is doubly important in the fermentation lab, in order to prevent unwanted pathogens from invading a ferment and causing it to taste off or, worse, become dangerous to eat. At Noma, we always err on the side of caution. If something you've made smells wrong—not just funky like fish sauce, but nose-stingingly rotten—trust your nose. If you taste a small sample and it turns your stomach, remember that your body is designed to reject things that may be harmful to you. When in doubt, throw it out. If you're ever unsure of a fermented product, toss it. The weeks or months of your invested time are not worth risking your health.

Potentially harmful microbes are ever present in the environment. Bacteria can multiply speedily, with or without oxygen, at temperatures ranging from 4.5° to 50°C/40° to 122°F, especially in moist, nutrient-rich environments. Of course, that describes the exact circumstances in which many fermented goods are produced. Both the World Health Organization and the United States Department of Agriculture recommend cooking foods sensitive to pathogenic contamination above 70°C/158°F before consumption. Now, that's a fairly severe safeguard, and obviously not possible for many ferments. That being said, you should be cautious, but not worried. Fermentation is meant to be a rewarding and exhilarating practice, but remember that you're playing with live ammo.

Throughout this book, we do our best to provide clear instructions that will produce safe and delicious products if followed closely. Don't eyeball measurements or take shortcuts. When a recipe calls for a specific salt content (above 10 percent by weight) or pH (below 4.5), it's to ensure that you're fermenting safely. But of course, the first step in preventing unwanted microorganisms from taking hold in a ferment is to make sure your equipment and hands are clean before they come into contact with food. While this is less important in certain cases, it's critical in other instances. When making koji, for example, you'll need to be sure the incubation chamber is properly sanitized before introducing the inoculated grains. And when working with your hands, wear nitrile or latex gloves to prevent contamination (except in places where a little bacteria from your skin can help things along, as with lactic-acid fermentation).

Now, what do we mean by "clean"? There is a difference between the level of cleanliness you would expect to find in a university biology lab and that in a home or restaurant kitchen. Let's define some terms. Cleaning means that you've removed visible dirt from the surface of objects. Soap and water will clean a surface but do very little to reduce the surface's population of microorganisms, good or bad. Sterilized implies that you've eradicated all life-forms—viruses, bacteria, fungi—on your equipment and your work surfaces (and sometimes even in the product you're looking to ferment). This is a level of certainty required in hospitals and microbiology labs. You'll never need something as serious as an industrial-strength autoclave for a recipe in this book. What we're looking to do for the recipes here is sanitize. To sanitize a piece of equipment or work surface implies that you've removed most microbiological life. That will be sufficient for our purposes. Running your equipment through a hot cycle in a dishwasher or steaming or boiling it for a few minutes is more than enough to ensure that you're working clean and sanitarily. If your equipment is heatproof, dry-heat sterilization is another option. Ceramic, glass, and metal containers and utensils can be baked in the oven for 2 hours at 160°C/320°F to ensure that they're free of contaminants.

For equipment or work surfaces that you can't pop into the dishwasher, there are common sanitizers intended for food production and fermentation like StarSan (available at many home-brew shops), distilled white vinegar (a sanitizing agent favored by grandmas the world over), and even household bleach diluted with water to 20 milliliters per liter (as long as you rinse with fresh water afterward). At Noma, for large items like crocks and buckets, we disinfect using ethanol diluted with filtered water to 60 percent alcohol by volume (ABV)—40 milliliters water for every 60 milliliters ethanol. (We dilute it because if the percentage of ethanol is too high, it can actually coagulate the proteins that make up the cell walls of many microbes and prevent them from dying.) We put the solution in a spray bottle and spray whatever needs to be sanitized, let it sit for 10 to 15 minutes, then wipe it off with a paper towel.

Finally, while a great deal of time is spent in this book introducing the amazing microorganisms responsible for fermentation, it's equally important to acquaint ourselves with the microbes that can make things go sideways. With a thorough grasp of pathogenic bacteria and molds, and what conditions they can tolerate, you'll be better equipped to keep them out of your products.

Clostridium botulinum

C. botulinum is the sporulating bacteria responsible for botulism. It is an anaerobic bacteria that thrives in nutrient-rich, warm environments. Its spores are commonly found dormant in soil and water, waiting for favorable conditions to propagate and release potent neurotoxins. Ingesting just a microgram of botulism toxin is enough to cause serious illness. You cannot taste or smell botulism toxin, and thus the only way to guarantee safety is through careful attention to best practices.

Though cases of botulism poisoning are rare, it's usually found in improperly refrigerated animal products or improperly canned vegetable products (where canning temperatures were not hot enough and/or the canning liquid was not sufficiently acidic). Given that the spores of the bacteria are often found in the soil, special attention should be paid when fermenting roots, bulbs, and tubers. When making black garlic, for example, you're keeping a root vegetable in an anaerobic environment at a warm temperature. However, C. botulinum cannot survive at a sustained temperature of 60°C/140°F. Your responsibility is to ensure that your heating chamber doesn't dip below that threshold.

C. botulinum also has great difficulty growing in fluid mediums with a water activity below 0.97 (achieved by salt concentrations of 5 percent or higher) and in acidic environments with a pH below 4.6. Many ferments in this book begin with salt concentrations lower than 5 percent and a pH above 4.6. However, the combined effect of moderate salt content and a gradually decreasing pH is usually enough to safeguard against malevolent bacteria. For instance, a vegetable brined at 2 percent salt will have a high enough salt content to inhibit C. botulinum while beneficial lactic acid bacteria lower the pH. If a ferment reaches a pH below 5 within the first two days and ends up below 4.6 by the time of completion, it is generally recognized as safe.

Escherichia coli

Many strains of E. coli are actually harmless and part of a normal gut flora, but some varieties can cause severe food poisoning. These bacteria are usually transmitted through poor hygiene or contaminated meat products. Cross-contamination of work surfaces and utensils is one of the more common causes of E. coli–related illness. Proper and thorough washing of vegetables in cold water will greatly reduce populations of the pathogen, should they be present. For products like beef garum, salt concentrations of 10 percent or higher will kill off the microbes. On top of that, the high temperatures at which garum ferments offer an added layer of protection.

Salmonella

Salmonella is a genus of rod-shaped bacteria often found in raw poultry products and unpasteurized milk and on unwashed fruits and vegetables. Doing everything you can to avoid cross-contamination from raw poultry is paramount in avoiding Salmonella food poisoning. For example, if you're cooking chicken wings for chicken wing garum, be sure to clean and sanitize any utensils before putting them back into action with the final, prepared ingredients. Like E. coli, Salmonella has a minimum water activity level of 0.95, meaning that salt levels above 10 percent will kill it off.

Pathogenic molds

There are thousands of wild and invasive molds that would jump at the opportunity to eat your fermentation project before you get the chance. Many microscopic mold spores are airborne, while others travel in water or on the backs of insects. Not all of them will necessarily be harmful, but if you didn't put the mold there yourself, it's best not to take the chance.

There are many instances in this book where we are trying to create the ideal environment for beneficial mold growth, so the best preventative measures you can take against pathogenic molds are cleaning and sanitizing. By eliminating any unwanted guests at the outset, you ensure that they won't spoil the party later. Another method is to overwhelm competing molds. With koji, we inoculate steamed barley heavily with A. oryzae spores in order to elbow out the competition. With ferments like garums and shoyus, the salt content retards mold growth. Frequent stirring and cleaning of the container walls will bring any spores on the surface out of contact with the air and drown them in a salty sea. For kombucha, keeping the surface of your SCOBY moist by basting it with liquid is often enough to keep it acidified and mold-free. Last, molds are easier to spot than other pathogens. When making something like miso, you can simply scrape away any mold that forms on the surface.

Potential of Hydrogen (pH)

Potential of hydrogen, or pH, is a hugely important measurement in chemistry, and a key factor to consider in fermentation. Simply put, it helps you measure acidity. The pH scale was first conceived in the Carlsberg Labs in Copenhagen near the turn of the twentieth century. It measures the difference in concentration in an aqueous solution between hydrogen ions (H+) and hydroxide ions (OH−), with every increase in numerical value from 0 to 14 indicating a tenfold change in ionic concentration.