Many of us eat yogurt for breakfast everyday; at my school, there's usually a tub of Chobani sweetened greek yogurt cups or some form of the thick, industrially produced version. However, the yogurt we know today bears some distinct differences to traditional yogurt, and fermented milk products. Yogurt is a byproduct of the Turkish name for fermented milk, and it originates from Southeastern Europe, specifically from the Caucasus mountain region. It has been mentioned in Ayurvedic documents written in Sanskrit as early as 6000 BC, and has existed for millennia as a means of preserving raw milk. At a time where pasteurization and homogenization of milk had not been discovered, there were limited ways of preserving milk, so people turned to drying or fermenting it in order to extend its shelf life. As such, every culture that produces dairy also has some product of fermented milk. The process of making yogurt usually relies on raw milk, because it contains a greater diversity of cultures. They are usually thermophilic bacteria, which are active at elevated temperatures between 110 and 115 degrees Fahrenheit, and the two most prevalent strains are L. acidophilus and L. bacillus. They are the only two strains required by law to be added to commercial yogurt, but many others such as Bifidobacterium bifidum or Lactobacillus casei are added due to their health benefits. Sandor Katz says in his book The Art of Fermentation that “According to geneticists Joel Schroeter and Todd Klaenhammer, humans “essentially domesticated these organisms over the last 5000 years through repeated transfer of LAB cultures for production of fermented dairy products”. Similar to many other fermented products, the drop in pH of the environment protects the milk from unwanted pathogens, which is achieved through the metabolic activity of LAB, which ferments lactose, broken down into glucose and galactose into lactic acid. The flavor of yogurt comes from this fermentation, which adds sourness, but according to a UCLA article on yogurt fermentation, “A mixture of various carbonyl compounds like acetone, diacetyl and acetaldehyde are also major contributors to the tarty yogurt flavor”. Making yogurt requires a starter culture, which contains the diverse series of bacteria that act upon the milk. The mix is then heated until it reaches a temperature of around 180 degrees, which allows the yogurt to thicken, due to the denaturation of certain proteins. It allows the proteins to form a gel and eliminates potential competitors, as yogurt is fermented until a pH of 5 has been achieved. This is the point at which the casein micelles lose their tertiary structure and the denatured proteins interact with other kinds, creating a semisolid structure and contributing to the final viscosity. After it is heated, the cultures are added, the milk is cooled until set and then fermented for anywhere from two days to upwards of a week. The rate of cooling and the initial temperature of the milk affect the final flavor of the yogurt, depending on the increased enzymatic and metabolic activity at higher temperatures. If the yogurt is cooled faster, it tends to be sweeter, whereas if it is left at room temperature, it can develop more acidic notes. Yogurt has been used in medicinal ways for thousands of years, but in the west, Ilya Metchnikoff, the pioneer microbiologist who studied longevity in Bulgaria gained notoriety when she attributed health to yogurt. This movement later spurred Dr Isaac Carasso to build a yogurt factory in Barcelona in 1919, which became known as Danone and then later changed to Dannon when he moved to America, creating the first industrial yogurt company. The yogurt Carasso made used a blend of bacteria isolated from Bulgarian yogurt, such as Lactobacillus delbrueckii (a subspecies of bulgaricus), and Streptococcus salivarius (subspecies of thermophilus), both of which have become commercial standards for the starter culture. However, this yogurt is not as strong in its resistance to unwanted microbes, as the diversity of yogurt cultures improves their stability. According to microbiologist Jessica Lee, with a single strain of bacteria, “a phage outbreak can quickly kill the entire bacterial population and end the fermentation process”, and even two isolated strains are vulnerable, as “eventually local bacteriophages evolve to be able to infect the few strains that make up that starter and slowly kill them off”. However, with multiple varieties of organisms present within the culture, if bacteriophages kill one strain, others can take over and protect the yogurt from spoilage. Thus, many yogurts are made using the "backslopping" method, where some of the original culture is added to the mix in order to jumpstart the selective environment that successful fermentation relies upon. There are many kinds of yogurt-like products in the world, but I will not be discussing kefir in this post. This is due to the fact that kefir is a little different, as it relies on a SCOBY (symbiotic colony of bacteria and yeast) that has evolved to create its own stable niche. According to Sandor Katz, kefir is a “symbiotic entity that self-reproduces; [and]combining each of the individual bacteria and fungal members will not result in a new kefir grain”. Since it involves a community of 30+ microbes that reproduce together via coordinated cytokinesis, and are connected by a series of biological molecules, the SCOBY requires another separate post to understand its complexity. Some of the yogurt products around the world are:
Yogurt is a perfect example of the diversity of global fermentation practices, as so many cultures rely upon milk as a dietary staple. It can be served thick, thin, sweet or savory, and it is gaining popularity in the culinary world as a way to thicken and add fat or flavor without as many calories as cream. The possibilities are endless: yogurt sorbet is becoming common, yogurt sauce is a staple in many cuisines, and dried yogurt (kashkh) is even added to some stews to enhance the fermented flavor. If you have the opportunity, try to look for real yogurt made from raw milk; try it once, and it might change your view on yogurt as a regular, sometimes boring breakfast option.
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Ah, chocolate: almost everyone loves it, and it's going extinct rapidly (time to stockpile :)). However, you might not realize how much work goes into the bar that you eat, and that the quality of the chocolate has a lot more to do with fermentation than you think. Going from cacao to cocoa can take up to a month, and it all starts with the fruit shown below, which through the process of microbial degradation creates the flavors we love in our chocolate, bitter, slightly acidic, sometimes spicy, and aromatic. This fruit, when mature contains mainly glucose and fructose, stored in the disaccharide form of sucrose. The beans are inside the white pulp, which has a low pH (3-4) and is high in sugar, because of the presence of pectin, saccharides, and citric acid, which later act as metabolites for micro-organisms. Well, why ferment chocolate in the first place, you might ask? The fermentation of the fruit has several purposes:
We all love chocolate, right? (Well, at least I hope you do; if not, I don't know if I can be friends with you). But how does it get its flavor? As it turns out, producing chocolate starts with the cacao beans, which are originally in the form of a fleshy, sweet fruit. It is still a so-called spontaneous curing process, in which microbes from the air inhibit the beans and transform their flavor. At the first stage of fermentation, yeasts dominate the cocoa environment, with their depectinizing activity that transforms the pulp into a liquid from a gel form. Hanseniaspora opuntiae/uvarum is often present at the beginning, due to its low ethanol and heat tolerance, but it is later replaced by saccharomyces cerevisiae, which thrives in that environment. The initial yeast fermentation reduces the pulp viscosity and allows for air to get into the fermenting mass, which encourages the aerobic-respirating bacteria to develop. The most important job of these yeasts is to produce ethanol from carbohydrates, i.e alcohol fermentation, namely sucrose. This disaccharide is then converted through invertase hydrolysis mechanisms in the yeast metabolism into glucose and fructose, the latter of which isn’t broken down by yeast. The ethanol produced will partly diffuse into the cocoa bean cotyledons (the embryonic leaf of seed-bearing plants) and either be oxidized into acetic acid , consumed by aerobic yeasts or disappear through sweating or evaporation. This all is an exothermic process, and it raises the temperature of the cocoa mass to 35–40°C within 48 hours. Yeasts are critical to the final flavor of the chocolate, as they create some of the acidity in the final bar, while developing volatile compounds that determine how a bar tastes. These organisms also produce acid, which acts as a buffer against bacterial contamination. After 24-72 hours, the air in the fermentation pulp allows for the growth of aerobic enterobacteria, namely LAB (lactic acid bacteria) and AAB (acetic acid bacteria). Ironically, some papers have found that LAB isn't necessary for the development of chocolate flavors. Nevertheless, it is a crucial step in the fermentation process, as LAB controls bacterial growth, encouraging fermentation through the control of the environment and acidity level. Glucose that is still available after yeast growth is fermented into lactic acid, acetic acid, carbon dioxide and/or ethanol, similarly to fructose. Although LAB is most active at this stage, since temperature, acidity and ethanol concentrations increase later on, LAB eventually declines in population size. The third and final stage is aerobic fermentation, where acetobacter species oxidize the ethanol produced by the yeasts into acetic acid, and the lactic acid produced by the LAB into acetic acid and acetoin. Sometimes, mannitol is also formed, as shown by Figure 1, but it depends on the type of acetobacter and yeasts initially present, and the type of bean. As these bacteria also cause an exothermic reaction, the mass's temperature increases to 45–50°C and even higher, limiting micro-organism growth and killing off the cacao and the yeast. As the acetic acid concentration increases and the cotyledon pH lowers (from 6·3–7·0 to 4.0–5·5), internal membranes of the bean cotyledon compartments degrade, so that substrates and enzymes mix. This is a key step in the fermentation of the bean, as it allows the seed germ to die due to the low pH (see Figure 2), and for all of the proteins and phytonutrients within the bean to break down into their constituents. Important flavor precursors are produced through this bioconversion, such as reducing sugars, hydrophilic peptides and hydrophobic amino acids, which later encourages the Maillard reaction during conching (roasting). Many companies now use starter cultures designed to inoculate cocoa communities, as it jumpstarts the fermentation process for bulk quantities. Valhrona, the high-end French chocolate company, has even invented a new fermentation technique that sets their chocolate apart: they add the pulp of local fruits to the fermented cocoa mash. According to their website, “the natural yeast and sugars of the fruit pulp work just like the sugars from the natural cocoa pulp in the first fermentation, and kick off the alcohol and acetic fermentation once again.”
Cacao originally belongs to the Mesoamerican continent, and it formed an integral part of Pre-colombian society. It was offered as a form of currency, worship, and trade; used for religious sacrifice, medicine, and often it was consumed unsweetened, in the form of a drink called Cacahuatl in Nahuatl, the ancient language of the Aztecs. Atole was/is another popular drink, made from corn, cacao, sometimes a little piloncillo (Mexican brown sugar), vanilla and canela (cinnamon). However, when the Spanish conquistadores came in 1519, chocolate transformed into a sweetened good and a major form of commerce for the European society, combined with the sugarcane trade from slaves and indentured servants in the Caribbean. Although the Spaniards managed to keep chocolate secret for a hundred years, it was eventually introduced to the French when the daughter of Spanish King Philip III wed King Louis XIII in 1615. Chocolates thus began to show up prominently in European pastries and confectionary shops, and were prized for their exclusivity. Europeans thus began to colonize cacao-producing areas and install plantations, as a means of making a large profit. When diseases brought by the European explorers killed native Mesoamerican laborers, African slaves were imported to work on the plantations. Chocolate was originally reserved for the aristocratic, however, as it was so expensive; it became accessible to everyone in 1828, when Dutch chemist Coenraad Johannes van Houten invented the cocoa press. The machine could extract cocoa butter from the roasted cacao beans, leaving behind a dry mass that could be pulverized into a fine powder to mix with other liquids and ingredients, poured into molds and solidified into what we know today as chocolate. This is proof that fermentation is essential to our lives: something many of us consume every day undergoes a rigorous process of decomposition and chemical transformation, under the guidance of a certain microbial community. Think about that the next time you take a bite: how far that bean has traveled to get from the fruit to your bar. Before I go into the specifics of certain ferments, I want to give a broader definition. Fermentation comes from the Latin food fervere, meaning “to boil”, and Noma in Copenhagen refers to it as “the transformation of food through enzymes produced by microorganisms, whether bacteria, yeasts, or mold”. It has been used as a method of preservation and flavor enhancement for thousands of years, starting in the Mesopotamic region and China, and chefs today are revolutionizing the variety of products that are subject to this process. According to Arielle Johnson, scholar of food science at MIT: “Microorganisms live in or on their food source, and biochemically transform it to extract energy, producing metabolites in the process. In general, a pool of larger molecular weight, and usually less flavor-active molecules - like starches and sugars - are transformed into a more diverse group of tastier, smaller molecules, such as amino acids, organic acids, esters, sugars, and aromatic compounds.” Fermentation relies on the control of the environment, specifically the salinity level, moisture content, pH (potentiation of hydrogen ions), and temperature, which affect the activity of the microorganisms. There are thousands of species that act upon substrates, but I will describe some of the most common ones below.
It's undeniable that fermentation carries health benefits: in many foods, new vitamins are introduced, like cyanocobalamin and pyridoxin (B12 and B6), as well as acetate (vitamin E). Furthermore, certain compounds like anti-nutrients that prevent absorption or raffinose, the compound in beans that causes gas and bloating are rendered inactive through the fermentation process, as microbes consume them as fuel. Although the link has not been proved for certain, there is some evidence in the scientific community that suggests that fermentation can improve the health of the gut microbiome, and improve the immune system's resiliency, which is currently under investigation.
Fermentation has become an intrinsic part of our lives, from cheese to chocolate to bread, and a new wave of this tradition has begun to influence how the restaurant world shapes its cuisine. At Noma, René Redzepi and David Zilber have built an entire fermentation chamber dedicated to researching various ingredients and microorganisms, which they incorporate into their menu. While fermenting at home doesn't have to be as complex as squid garum or black garlic miso, simple saeurkrauts or kimchi can easily be made (and nothing compares to a version you make yourself!). As this is a topic river, I aim to cover only some of the basics, but I will get more in depth with specific products in the future. Controlled rot. Almost decaying, straddling the line between edible and dangerous. Despite the negative connotation or the smell, fermentation has existed for thousands of years as a method of preservation. It improves the nutritional profile of ingredients, retains moisture and texture, and introduces new flavors not present in the original food. Sounds almost too good to be true, right? The best part is that it is within reach to ferment at home, as we eat fermented foods everyday (think yogurt, bread, wine, even chocolate!) and it would be nice to learn how to make these products ourselves. Every culture has a fermented product, as before the refrigerator, that was the way that people extended the shelf life of their meal. Some, like kimchi have even become cultural hallmarks, constituting part of a national identity and regarded as an integral tradition.
Through the course of this blog, I aim to explore global fermentation methods, explaining the cultural significance, history, science and method of preparation of each. There will be some recipes along the way, as it is a process of discovery, trial and error, but they are only suggestions for what can be done with ingredients. There are hundreds of books out there on the subject, and numerous websites with far more depth than I could cover, but I want to distill that information so that it is more accessible. Hopefully, the blog will accomplish two things: 1)convince people that fermentation is not as daunting as it sounds, and it is delicious to try at home, and 2)food and culture are intrinsically bound, and fermentation represents just one facet of their intersection. As I explore the world, from kimchi to yogurt to vinegar, it is my wish that those who read this may understand why fermentation holds potential to make food that much better. I truly hope that you enjoy reading as much as I, and that as you try new things, you might even discover that you never knew how much you had missed. - Ben |
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May 2020
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