Yeast Growth in Different Media
Abstract
The production of yeast is the most important step in creating alcohol. In this experiment we will test the rate at which yeast is produced in different. By using four different medias we were able to compare the yeast growth in each of the media. The yeast was tested by inoculating colonies in (YPD) yeast extract peptone dextrose, PD (potato dextrose) and ME (malt extract), and finally wort media. Each media was inoculated at 27°C. The data was recorded every 30 minutes as the yeast grew continuously. This was to show the effect of each media on yeast’s growth. The results concluded that the yeast extract peptone dextrose media (YPD) had the most amount of growth.
Introduction
In the process of brewing beer, the knowledge of microorganisms and their chemical reactions is extremely important. When alcohol is produced, the yeast converts sugars, common ones such as fructose, sucrose, and glucose, into alcohol and carbon dioxide as well. In
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the brewing process, the yeast obtains the sugar from hops, barely, or other grains. By following all the details needed for a successful brew, yeast will be allowed to reproduce and develop during the process. By changing the different types of media we can test which media will allow the yeast to develop and grow faster, compared to the other medias.
In our test of the hypothesis that yeast will grow faster in the YPD media, we can assume this would test correctly because YPD is filled with more nutrients. Due to the amount of nutrients in YPD, yeast will will be able to consume them and help enhance its rate of reproduction and development. This will also allow the yeast to have more nutrients for its offspring. This increase in nutrients will also lengthen the amount of time while in the exponential and stationary phase of the graph.
In the testing of yeast growth in different medias, yeast was inoculated onto YPD, PD, and ME media which was then incubated at 27°C for 24 hours. Data was collected from the media every 30 minutes. After data collection was completed, it was placed into an excel spreadsheet and then created into a graph that shows the growth and development of yeast in each media.
Materials and Methods
The experiment uses three growth mediums for the experiment: YPD (yeast extract) PDB (potato dextrose broth) and Malt extract. An overnight cultures were also prepared for this experiment. The yeast culture was inoculated and then placed into the three medias separately, using a sterile pipette for each inoculation. Inoculation can be described as pipetting a sample
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from the culture and transferring it into the media, disposing the old pipette and replacing it with a new one each time. This process will be repeated until all three media have a yeast culture in them. Once the inoculation is complete, the media with the yeast inside it will be incubated for 24 hours at 27°C. The media will also be shaken continuously while in the incubator. Data is collected every 30 minutes while in the incubator, and once completed, a sample will be taken from each media. After a sample is taken from each media, it is transferred into a glass cuvette and then placed into a spectrophotometer. A spectrophotometer is a machine that measure the turbidity of a fluid. When the spectrophotometer is calibrated, the curettes that contained the samples were placed into the machine and had measurements taken. An additional media sample of wort was used and has measurements taken and placed onto the excel sheet along with the other three medias.
The nutrient make up of each media is very different. YPD contains 10g of yeast extract, 20g of peptone, and 20g of dextrose. All of the components are very suitable for yeast growth and development. Peptone is used by yeast to break down the food molecules it ingests and dextrose is an energy source. The second media is PD and contains 4g of potato starch and 20g of dextrose. The final media is malt extract (ME). It contains dehydrated malted barley.
Results
Our results show us numerous details and trends about the yeast growth in the four different medias. The most important result is that the YPD media shows the most growth and development. As you can see from the graph, the final YPD concentration is the highest when
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compared to the other three media. The media with the lowest absorbance is malt extract with a significant lower absorbance than the other media. ME also has the most insignificant continuous increase in absorbance when compared to the other media. When comparing the Potato Dextrose (PD) plot to the other 3 medias, it has the longest growth phase over time, whereas the other media have a sharp increase and eventually reach their maximum absorbance.
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Along the X-axis we have time and along the Y-axis we have Absorbance
Time (min)
YPD
PD
ME
Wort
35
0.169
0.168
0.284
0.247
60
0.18
0.182
0.373
0.291
113
0.225
0.228
0.415
0.373
150
0.285
0.234
0.52
0.45
180
0.404
0.256
0.497
0.605
210
0.471
0.288
0.552
0.717
240
0.576
0.348
0.583
0.879
270
0.802
0.366
0.617
1.112
300
1.067
0.422
0.677
1.309
330
1.358
0.431
0.667
1.489
360
1.652
0.468
0.711
1.702
390
2.033
0.509
0.746
2.056
450
3.402
0.621
0.832
2.921
510
5.611
0.729
0.948
4.023
570
8.483
0.881
0.963
5.612
630
10.792
1.078
0.968
7.324
690
11.312
1.314
0.971
9.037
810
11.578
1.951
0.981
9.156
930
11.734
2.699
0.986
9.434
1050
11.798
4.102
0.991
9.707
1170
11.912
6.013
1.012
9.897
1290
11.989
9.101
1.019
10.098
1440
12.07
11.25
1.021
10.14
Discussion
From our data collection we can assume that our hypothesis is correct, in that YPD media will have the most growth and development due to its multiple nutrients when compared to the other media. YPD most likely supports for maximal growth because it contains yeast extract, peptone, and dextrose. Peptone is what enhances yeast reproduction and dextrose is the energy source for the yeast. In the data collection table at the maximum time recorded of 1440 minutes, the absorption rate for YPD was 12.07 which was significantly higher than the other media. YPD also took the shortest amount of time to reach its maximum absorbance rate. YPD has a very constant increase in absorbance concentration as well. When viewing potato dextrose (PD), it’s absorbance concentration was almost as high as YPD. However, it does not have an increase compared to the YPD media. PD begins its absorbance rate very small and remains that way around minute 630, where it begins to make significant increases in absorbance. Looking at the malt extract (ME) media, it appears that the yeast absorbance rate finishes with the lowest concentration out of the four media. A rate significantly less than the other media. However, ME at the first data collection has the highest starting absorption, but as time increases shows no significant increases in concentration.
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Finally, when viewing the data for Wort media, it has a steady increase with a high starting concentration but does not finish as high as YPD or PD. Therefore we can conclude that YPD would be the optimal media for yeast growth and development, with PD and Wort not far behind.
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