Fermentation: Yogurt Project

Leslie Gutierrez, Kelly Diep, Shirley
Ms. Malonek
Biology 1/2 
25 November 2014

1. Fermentation Project: Yogurt

   Task: 
   

   • a recipe in metric
   • pictures of you making the product and tasting the product
   • a paragraph describing in detail what type of fermentation is going on

   
   Recipe
   
   

   1. Place 0.946353 Liters of 2 percent milk in a large saucepan over medium-high heat; cook until it reaches 180 degrees, stirring occasionally to prevent scorching, 5 to 7 minutes. Let cool to 115 degrees.
   2. Whisk together 0.236588 Liters of the heated milk and 0.0443603 Liters of plain low-fat yogurt. Stir into remaining milk.
   3. Transfer to a 0.946353 Liters mason jar. Wrap jar (without lid) in 2 clean kitchen towels, completely covering sides and top. Let stand undisturbed in a warm place until yogurt has the consistency of custard, 4 to 5 hours.
   4. Refrigerate uncovered jar; when it's cool to the touch, about 30 minutes, screw on a tight-fitting lid.

   • What type of fermentation is going on?
   • The type of fermentation that demonstrated by creating yogurt is lactic acid fermentation. One produces yogurt through the lactic acid fermentation of milk with harmless bacteria. By decreasing raw milks pH it causes the milk to congeal, or increase in temperature, causing it rot and become yogurt. The bacteria in lactic acid fermentation, lactic acid bacteria, are a diverse group of bacteria that are able to ferment various sugars which then produces lactic acid plus other waste products. In general, lactic acid fermentation is the "anaerobic microbial breakdown of sugar, yielding energy in the form of ATP and releasing waste products, specifically lactic acid." In other words, yogurt is simply milk fermented by lactic acid bacteria. The two species of bacteria that are most commonly used to make yogurt are Lactobacillus bulgaris and Streptococcus thermophilus. These types of bacteria then ferment the sugar found in milk, or lactose, into lactic acid and other compounds with unique flavors. In addition, the lactic acid causes the milk proteins to clump together, giving the yogurt its characteristic thick texture and  its delicious taste. According to education-portal.com, if you pulled out 1 gram of finished yogurt, you could find up to 100 million lactic acid bacteria,  which illustrates overall just how well lactic acid bacteria "are able to thrive by fermenting just lactose." 
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   Source: http://www.marthastewart.com/948811/homemade-yogurt

   

   Leslie cooking the yogurt!
   
   

   

   Leslie tasting the yogurt! YUM! 

   

    November 25, 2014