What/ Why:
In this lab we made yogurt. We made yogurt because it is an easy way to go through lab procedures and a easy way to learn about bacteria. In the lab, what were essentially introducing some bacteria called L.bulgaricus, S.thermophilus, B.regularis, and L.acidophilus to pasteurized milk. It is also a great way to learn about how bacteria is made and multiplied. How: We made the yogurt with 200 ml of half and half, 3.5 grams of dry milk powder, and a spoonful of already existing yogurt. First, we measured our milk and poured it into a mason jar. Second, we heated up the milk in a heated water bath. We left the milk in the water bath for about 15 minutes because around that time, the milk should be around the right temperature we wanted it to be. Third, we measured the dry milk and added that into the milk. Then, we got a dollop of yogurt that was already made and also added that into the milk. Next, we stirred the ingredients up so everything is evenly distributed. We also weighed the jar to see if there was any weight change afterwards when the mixture became yogurt. After that, we placed the mason jar into the incubator that was heated at 23 degrees Celsius and the jar was left in there for about 20 hours. Once the jar was taken out of the incubator, it was placed in the refrigerator for a couple hours. When the yogurt has cooled in the refrigerator for a couple hours, it can be taken out to eat. Observations: When the yogurt was ready to eat I opened the jar and the first thing I noticed was that there were some air bubbles on the top of the yogurt. When we stuck a spoon into the yogurt, we noticed that the spoon stood up and didn't move around. That told me that the yogurt isn't liquidy and it is thick and dense. When I was scooping the yogurt out and was playing with it, I noticed that the yogurt had a sour cream like texture and consistency. When I tasted the yogurt, I noticed that it wasn't what I expected the yogurt to taste. It had a sour and citric flavor and it wasn't as milky as I thought. Since it wasn't sweet enough for me, I added sugar and I thought it made it taste WAY better. Data: As I said before, we weighed the yogurt before it was placed in the incubator and then afterwards. Before it was placed in the incubator, the weight of the yogurt was 433.87 grams. When the yogurt was incubated and refrigerated the weight of the yogurt was 433.77 grams. The only weight difference was about 0.1 grams. Analysis: The yogurt didn't turn out the way that I wanted it to but that helped me learn what nit to do if I ever did this lab again. One change I would do was to not put the yogurt in the incubator as long as we did because I learned that the longer the yogurt is placed in the incubator, the sourer it gets. Next time, I would just leave the yogurt in for about 8 hours instead of 20. I would also make sure that the correct temperature is met because when I was heating up the milk, I didn't check if the to see if the correct temperature (55 degrees Celsius).
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December 2015
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