Charming Chemistry Creations: Yummy Yogurt

Yogurt is my first choice of breakfast’s on the go when I am running out the door to class. I love yogurt for its creamy texture and sweet flavors. Are these attributes common among all yogurt’s or just Yoplait’s?

Yogurt comes from the Turkish word “milk” and also means “thick” (McGee, 48). Common in ancient cultures, yogurt did not hit Europe until the 20th Century. At this time, scientist were able to identify the property of fermented milk and the bacteria produced. It was this bacteria that enhanced the natural bacteria in the gastrointestinal tract and prevented destructive bacteria from infiltrating the body. Yogurt flavors were not always Boston Cream Pie and Wild Strawberry. Up until the 1920’s, only plain yogurt existed. Yogurt is made from fermented milk, bacterial cultures and in some cases, flavorings and sugar. We made plain yogurt from fresh milk and plain yogurt. The plain yogurt was considered our starter and already contained the common bacteria Lactobacillus and Streptococcus. Live cultures can be bought that contain the bacteria, but on our case, we used plain yogurt. The milk was heated which destabilized the proteins (McGee, 48). The heat denatures the whey protein Lactoglobulin. The milk was heated via a double boiler to prevent scalding the milk. A double boiler made it easier to regulate the temperature of the milk to 185 degrees. The milk was removed from the heat and the plain yogurt was added, which means the bacteria was added. At this point, the milk was still liquid and remained the white color. The casein protein was broken down by Streptococcus and allowed to slightly bind with other casein proteins. The casein proteins were able to bind together at a few spots, creating a matrix structure and not chunks as in the cheese. This matrix gives yogurt its thicker texture. The circular structure of Streptococcus allows the bacteria to function at higher temperatures. At this elevated temperature, the bacteria are allowed to grow and ferment the milk by producing lactic acid (Probiotic.org, 2009). The yogurt was covered with plastic wrap to seal in the heat and left untouched for the milk to set. At two hours, the yogurt had not gelled yet, and remained liquid. The finishing appearance of the yogurt is thinner than store bought yogurt because store bought yogurt contains corn starch, which is a thickener. The starch gives the yogurt the creamy texture we know. Greek yogurt is even thicker than normal yogurt because the water the whey are strained out of the yogurt (Greek yogurt vs..., 2011). In the future, I would add more sugar to the yogurt, so it is sweet and the sugar also acts as food for the bacteria.