Yogurt Lab Discussion

     Because I was starting this lab with little introduction, I was a little confused throughout the experiment. Therefore, I am not that confident in the results.
     In tube 1 (just milk), the milk was sour but the texture was normal. Airborne bacteria probably contaminated the milk and then divided during inoculation. The milk was spoiled, but these particular bacteria were not yogurt-ness bacteria, so the texture did not change.
     In tube 2 (milk and yogurt), the substance was thicker and had a smell like yogurt. I was unsure whether this was because the milk actually turned into yogurt or because yogurt was added. However, I am assuming that the yogurt really did change the composition of the milk because the whole sample changed even though we only added a tiny amount of yogurt. The bacteria in the yogurt must have created the original yogurt, as well as altering our milk sample.
     As we expected, tube 3 (yogurt, milk, and ampicillin) was absolutely unaffected by the experiment. The smell and consistency were normal, as was the pH, because all the bacteria that could have altered the milk were killed by the ampicillin.
     Like tube 1, tube 6 (milk and E. coli) also resulted in a sour smell with normal consistency. The smell of this sample was overwhelmingly sour and made me want to throw up. E. coli seems to spoil milk but not turn it into yogurt.
     Our pH readings may have been a little skewed, but it is clear that every tube subjected to bacteria had a lower pH than the tube with ampicillin. Tube 1 had the lowest pH (5), and tubes 2 and 6 had a pH of 6. These numbers don't seem to make sense because the milk with lowest pH should curdle as casein proteins denature. Tube 2, however, was the only one that curdled.
     There were a few sources of error that may have affected the results of the experiment. First of all, if the inoculating loops touched any non-sterile surfaces, the tubes could be contaminated with outside bacteria. Also, the colors on the pH scale are so similar that someone could conclude a strip shows a pH of 5 when it is really closer to 7. Finally, we may have used the vortex for too long, which potentially could kill the bacteria by breaking open the sturdy cell walls.
     Despite some confusion, I believe our results turned out fairly accurate. Most importantly, we had a great time in our first lab of the year.