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Fermented foods are all the rage — you can’t help but notice. This could even seem quite banal if you consider that humans have been fermenting food for millennia and many of the things we eat today are fermented: bread, cheese, yogurt, beer, and wine, for instance, are fermented. The history of fermentation is thus quite long. However, the science behind fermentation — zymology — only began being intensively studied during the 17th century with the chemical assays by Antoine Lavoisier, and a century later with the discovery of the role of yeasts in alcoholic fermentation by Louis Pasteur, and the importance of yeast enzymes discovered by Eduard Buchner.
Fermentation is the activity of microorganisms (fungi and bacteria) that proliferate in a certain foodstuff, thus consuming some nutrients for the obtention of energy. This reaction is mediated by enzymes that hydrolyze the ingredient’s proteins, lipids and polysaccharides, transforming them into different, tastier and more aromatic molecules, and producing compounds such as ethanol, lactic acid, and acetic acid. The latter are pivotal in the protection of the fermented food against the activity of harmful microorganisms. You may not want to think of it this way, but fermentation is actually controlled spoilage. The result is, however, delicious and useful.
But other than making food tastier, does fermentation have any other purpose? Of course, it does. Some of the advantages of fermentation include the extension of the food’s shelf life (think of monumental sea travel and desert crossings), especially in unfavourable climates, but also the detoxification of certain compounds, the inhibition of pathogenic microorganism growth, the preservation of vitamins, and nutritional enrichment by simplification of molecules and concentration of nutrients.
The popularity of fermented foods that were otherwise obscure has surged also due to the interest and work of several chefs and personalities that have invested their time in the discovery of this wonderful world. The Nordic reinvention of fermented foods by restaurants such as Faviken or Noma, the Art of Fermentation by Sandor Katz, Momofuku’s fermentation lab, and the propagation of Asian fermentation techniques and cultures have changed the face of restaurants and private consumers. Also, increasing evidence of the health benefits of probiotic foods has put fermented foods in the limelight. So, let’s talk about a series of fermented foods you might be familiar with, and some that you’ve probably never heard of. Ready?
You can’t miss olives in any decent Portuguese feast. Never make the sad mistake of eating a fresh olive picked from the tree. The truth is that olives in their natural state are truly unbearable, due to the prevalence of oleuropein, an extremely bitter compound. Curing is the best way to remove this compound from the olive. The olive is slit and placed in a brine containing (or not) 1-3% of sodium hydroxide, and the brine is changed a few times. The brining process helps the natural occurrence of fermentation, which is mainly conducted by lactic acid bacteria and also fungi. If the olives are not previously treated the fermentation process is much longer and dominated by fungi, which induce alcoholic fermentation. This type of fermentation completely changes the flavour profile, resulting in more bitter and fruity olives.
COCOA AND COFFEE
Fermentation is mandatory to make this both cocoa and coffee consumable. Cocoa, Theobroma cacao, has its precious grains covered by a pulp that rests inside an oblong fruit. After harvesting, the fruits are opened and the pulp starts to ferment by the natural microflora for a period between 2 and 8 days. The fermentative process doesn’t happen in the grains, but rather in the pulp. During the fermentative period, lactic acid bacteria and yeast will alternatively prevail by consuming the pulp’s nutrients. Eventually, debris from fermentation will drill into the grains, thus allowing the incorporation of compounds with fruity and floral aromas. The process is then completed by drying, roasting, and grinding of the grains. When regarding coffee (Coffea arabica or Coffea canephora), there are several approaches considering its fermentation. The main aim is to remove the outer layer that covers the coffee grain. The most traditional method (dry) consists in drying the whole coffee fruit in the sun, thus promoting aerobic fermentation. The sugars still present in the fruit will favor a diverse fermentative microflora. This type of fermentation is common in regions with little rainfall and results in a coffee with full body and more aromatic complexity. There is also the wet method, where the grains without the mucilage are placed underwater to stimulate fermentation. Another method is the semi-dry, which is in effect a combination of both the dry and the wet fermentations. We couldn’t find solid information regarding the most common fermentation methods for arabica and robusta coffees, so we’ll keep that one on the hold for now. But if we want to talk about the world’s most expensive coffee, then that’s another story. A small tropical rainforest dwelling feline, the civet, feeds on coffee grains. You can guess the rest of the story. During the digestive process, the coffee is submitted to a unique type of fermentation inside the cat’s gut and is released intact in its feces. Those who have tried it say it’s chocolatey and less bitter: one kilo of Kopi Luak coffee can be worth 1000€!
Sauerkraut is simply fermented cabbage, and it’s also the German’s favourite side dish for sausage. The cabbage is finely chopped and covered with salt, pressed and left to ferment at room temperature for a few weeks. The main action is developed by lactic acid bacteria that produce acids (lactic acid and acetic acid, for instance), aromatic esters, gas and small amounts of alcohol. The final result is a vinegary cabbage which is slightly sour, somewhat salty and quite aromatic; a great side for heavy dishes. In many locations, spices such as juniper berries and cumin are added to sauerkraut while it is being fermented.
Katsuobushi is an elaborate Japanese product that comes from bonito tuna (Katsuwonus pelamis). To produce it, the tuna’s meat is boiled and hot smoked for several days. Then, the fish meat is inoculated with fungi (e.g. Aspergillus spp. and Eurotium spp.) and left to ferment for a few weeks. After the fermentation, the meat is dried in the sun and the fungi are removed. The flavour profile of katsuobushi can be translated into smokiness, saltiness, and the ultimate umami flavour, especially due to the presence of ionosinic acid. Katsuobushi is traditionally used in the form of translucent flakes to make dashi, and to season other dishes such as the scary centenary egg (pidan), ramen or takoyaki.
Kefir is a close relative of yogurt, but more acid, tangy and slightly alcoholic. It is believed to have originated from the North Caucasus. The recipe is simple: cow, sheep or goat’s milk is inoculated with kefir grains and left to ferment from around 24 hours. Simple, right? But the secret is in the grains. Kefir grains are a symbiotic complex of yeasts and lactic acid bacteria (e.g. Leucnostoc spp., Lactobacillus spp. and Lactococcus spp.), that are inserted in a polysaccharide matrix named kefiran. The diversity of probiotic bacteria found in kefir has lead to the discovery of several health benefits.
Kimchi is a fruit of ancient tradition and is conceivably the most iconic dish for Koreans. The importance of kimchi as a source of vitamins, minerals, and fibers has been emphasized in the Korean diet. Kimchi can be made from a great variety of fruits and vegetables, and also mushrooms. The familiar nappa cabbage is indeed the most widespread version, but kimchi is often seen made of radish, ginger, soy sprout, melon, and many other base ingredients. As expected, the variety of kimchi styles is also vast. To prepare kimchi, the chosen ingredients must be brined or dry-salted for a few hours. Then, a base of gochugaru (chili powder), jeotgal (fermented seafood), and other seasonings are added and left to ferment at low temperature for a few days to weeks. The fermentation is handled by the microorganisms that are naturally present in the vegetables, and at some point dominated by lactic acid bacteria. The result is an intense flavour, which is spicy, somewhat sweet, quite salty, fresh and sour.
Consumed for millennia in Japan, the true origins of this fermented tea beverage are still unknown. The secret for the elaboration of kombucha relies on the work of a blobby thing called SCOBY*, a symbiotic complex of yeast (ex. Saccharomyces spp.) and bacteria (ex. Acetobacter spp.). The addition of SCOBY to sweetened tea initiates fermentation, and in the right conditions you end up with a slightly fizzy kombucha, acidic and with a hint of sweetness. Truth be told: the taste of kombucha can be somewhat described as tea with vinegar and a tablespoon of sugar, but different fermentation protocols may result in very diverse and contrasting flavors. It should also be mentioned that due to the occurrence of alcoholic fermentation, kombucha has a small percentage of alcohol (0.3-0.5%). *Symbiotic Culture of Bacteria and Yeast
Kvass is such a relevant and traditional beverage in Russia that it even got nicknamed as the ‘Communist Coca-Cola’. Ironically, Coca-Cola itself is now producing kvass. There are hundreds of different recipes for kvass. In general, the principle is the use of dried or old bread, especially rye bread, which is placed in a jar with mint and submerged in boiled water. It is then left to rest overnight. The bread is then discarded, the liquid is saved. Sourdough — which will promote fermentation — honey, and sometimes fruit, are added. After fermenting for a day or two, the kvass will be quite carbonated and ready to be bottled. In the end, kvass will have an alcoholic degree of 0.5 to 2% and have a fresh, bubbly, bread taste with a touch of sweetness.
PRESERVED LEMONS (LAMOUN MAKBOUS)
Preserved lemons are considered a delicacy in North Africa and Asia. The preparation is quite simple: the lemons are washed, sliced into quarters and covered with salt. They are then left to ferment in a warm place (or even under direct sunlight) for a certain period of time, which may vary from a few days to several weeks. Before use, the salt is washed off and the peel is saved, as it conserves the best aromatic features of the lemon, and where a complex umami flavour is also developed. Preserved lemons are used in desserts and to add complexity to savoury dishes.
Miso paste can be obtained by boiling grains of rice or barley, and also soybeans. The addition of Aspergillus oryzae (koji) is the essential starting point of the fermentative process. This first fermentation results in a mixture that is also named koji, and traditionally, this koji goes through a process of barrel aging. At this stage, there is the addition of a great amount of salt to cease the growth of A. oryzae and promote the growth of halotolerant lactic acid bacteria and yeast that will slowly shape miso’s flavor by unfolding proteins and sugars into simpler forms. Along the way, the Maillard reaction between amino acids and sugars will contribute towards browning and deepen miso’s flavor. Miso can be divided according to color: red (akamiso), white (shiromiso), yellow, brown and black and also by flavor profile, from lighter (white miso) to stronger (darker miso). Variations in A. oryzae strains and the fermentation temperature will result in different kinds of miso. Miso is traditionally used for miso soup, marinades, and sauces.
Soy sauce is quite distant from Western culture. It began appearing meekly in Chinese restaurants, only to later gain full-blown exposure during the sushi craze at Japanese restaurants. Next time you’re headed to the supermarket to buy some soy sauce, think twice before buying the cheapest option. Let us explain. These days, the soy sauce industry has two main means of production: traditional and chemical. The traditional method consists of a lengthy fermentation process that involves soybeans, salt, and the fungus Aspergillus oryzae. This ancient method is based on a mixture of boiled soybeans and toasted wheat, where A. oryzae (koji) is inoculated. During the first step of fermentation, several important chemical reactions occur, namely the transformation of protein into amino acids and starches into simples sugars. The second step of fermentation involves an addition of brine to the soy paste to halt the action of A. oryzae. and promote the growth of salt-tolerant bacteria. This is the longest phase — it may last several months or even years — and it will add complexity to the flavours and aromas through the production of acids, in particular of glutamic acid, the major player in the development of umami. In the end, the paste must be pressed to obtain the soy sauce. Meanwhile, most industrial soy sauce is produced by the chemical method. The soybeans are hydrolyzed, mimicking the role of koji, and the colour and flavour are obtained by additives such as caramel and corn syrup. However, a great amount of Japanese soy sauce is in fact obtained by mixing equal parts of traditional and chemical soy sauce, and this product is commonly known as koikuchi shoyu.
Natto is in a limbo between being the next food trend or something that no one wants to hear about. It is hard to explain the flavour and texture of natto, so it’s easier to explain how it’s made. Natto has been produced in Japan for several centuries, and it is really quite simple. Soybeans are boiled and Bacillus subtilis bacteria are added; these bacteria will completely transform the soy bean’s original flavour. The fermentative process lasts around 24 hours at a relatively high temperature. As a result, there is an aggregation of small beans united by a viscous slime that will worm a web of unbreakable strings. These transparent strings are a result of B. subtillis metabolism, a type of biofilm, and are composed of long chains of glutamic acid and polysaccharides. This is the reason why these strings are often called the real umami strings. Of course, it’s not the umami us mortals are used to see around. Natto is usually consumed in salads, as a side for white rice, or even in a melted cheese sandwich. Yet, when heated, natto loses some of its pungent flavour.
You might very well end up doing your own pickles. In part, because of that forgotten jar of fake cucumber pickles in your fridge. You and I have been eating fake pickles for a while, you know. That’s because supermarket pickles are usually made by adding a solution of vinegar with salt, sugar, and spices to a pre-boiled vegetable. This doesn’t allow fermentation to occur due to the inhibitory effect of the vinegar, and also because of the destruction of the vegetable’s natural microbe flora due to boiling. To make fermented pickles, the vegetables must be submerged in a brine. Then, the veggie’s natural microbiota will thrive and ferment in an anaerobic environment. Real pickles are acid (but not vinegary), due to lactic acid fermentation, and also fruity and much more complex.
The composition and consistency of tempeh are very similar to those of tofu. Tempeh is obtained by fermenting with soy with Rhizopus oligosporus ou Rhizopus oryzae fungi for 24 hours. The filaments of these fungi unite and partially digest the soy. The high temperature and humidity of Indonesia present the most favourable conditions for the natural occurrence of this fermentation. As salt is not added during the fermentation process, tempeh is highly perishable. This handicap has meant that tempeh did not suffer from mass globalization, unlike many other soy-based products. The flavour of tempeh is nutty and mushroomy, making it a very plastic ingredient, as it can be grilled, fried, boiled or even stewed.