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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May 2020
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