This experiment examined the effect of temperature on the growth rate of Saccharomyces cerevisiae. S. cerevisiae samples were stored at temperatures ranging from 5 to 37 degrees Celsius. The highest growth rate was observed at 5 degrees Celsius, with a doubling time of 49.7 minutes. Growth rates were similar and doubling times were around 18 hours at temperatures of 25, 30, and 37 degrees Celsius. Thus, lower temperatures supported faster growth of S. cerevisiae.

1. Experiment 1.
The affect of temperature on Saccharomyces cerevisiae.

2. Introduction to Saccharomyces cerevisiae.
• Saccharomyces cerevisiae is an eukaryotic microbe.
• Approximately 160 species of wild and laboratory yeast.
• Yeast is a facultative anaerobe.
• 1 gram of dried yeast contains approximately 25million cells.
• The word, Saccharomyces cerevisiae, can be broken down into different Latin
words. Saccaro, meaning "sugar", myces, meaning "fungus", and cerevisiae,
meaning "beer", thus translating into "sugar fungus of beer".
• It is believed to have been originally isolated from the skin of grapes (one can see
the yeast as a component of the thin white film on the skins of some dark
coloured fruit).

3. Role in food production
• Bakers yeast…The leavening agent
• Brewers yeast…The fermentation process
• In 1879, Britain introduced specialized growing vats for the production of S.
cerevisiae

4. Method.
• T0 Saccaromycies cerevisae
prepared from nutrient broth
to a dilution of 1000 and
stored at the optimum
temperature for mesophilic
yeast strains of 25 degrees
celsius.
• T2 Saccharomycies cerevisae
prepared in solutions of
10000 and 100000 and stored
at the below range of
temperatures to observe and
measure growth rate;
5 ℃ 25 ℃ 30 ℃ 37 ℃

5. Results.
T2 agar containing the formed yeast colonies (or lack of).

6. Results; raw data calculations.
Calculations used;
Log T2 – 3.95 = ng
0.301
180 = doubling time
ng and here’s what you could have won…
Saccharomyces cerevisiae on agar plate

7. Experiment results.
TEMPERATURE; DEGREES CELSIUS COLONY FORMING UNITS (CFU) DOUBLING TIME
5 110000 49.7 mins
25 10000 ▶18hrs
30 10000 ▶18hrs
37 ◀ 10000 ▶18hrs
Table of T2 results

8. Results.
0
200
400
600
800
1000
1200
0 5 10 15 20 25 30 35 40
GROWTH RATE OF SACCHAROMYCES CEREVISIAE AT VARIOUS
TEMPERATURES.
Temperature in degrees celsius.
Time in minutes.

9. Results.
0 200 400 600 800 1000 1200
5
25
30
37
Growth rate of Saccharomyces cerevisiae at various temperatures.
Time in minutes.
Temperature in
℃

10. Discussion; in relation to experiment
• Sources of error; diluting accurately, using the measuring
pipette correctly, bit of spillage, contamination by skin cells
causing yellow/ orange colonies, institutionalised specimen,
calculating the Log … correctly
• Psychotrophic sample; Saccharomyces response to heat stress
of the experiment, though the temperature conditions were
selected for a mesophile.

11. Discussion; in relation to food safety
• Yeast is used to convert glucose to alcohol and achieve the end product
in brewing, BUT is sensitive to heat (as evidenced by experiment) so
cannot be heat treated to ensure product free from undesirable
organisms
• Requires another hurdle to prevent contaminants hazardous to
health…
• Yeast grow well at acidic pHs. They grow best between pH 4 to pH
6. During growth and fermentation the pH drops to about 4.1-4.2 and
in some cases even lower. Yeast can survive at very low pH, as low as
2.0.
• The low pH of beer, which is generally lower than 4.5, is one of the
main reasons why it provides a poor growth medium for many
bacteria. pathogens like E. coli or C. botulinum cannot grow in beer
and it is therefore safe to even drink beers that have been infected.

12. References.
• Briggs, D.E., Guest, Brookes, P.A. and Stevens, R. (2004) Brewing, science and practice science and practice.
Cambridge: Woodhead Publishing.
• Deegenaars, M.L. and Watson, K. (1998) ‘Heat shock response in psychrophilic and psychrotrophic yeast
from Antarctica’, Extremophiles, 2(1), pp. 41–50. doi: 10.1007/s007920050041.
• Kishimoto, M. (1994) ‘Fermentation characteristics of hybrids between the cryophilic wine yeast and the
mesophilic wine yeast’, Journal of Fermentation and Bioengineering, 77(4), pp. 432–435. doi: 10.1016/0922-
338X(94)90019-1.
• Srivastava, K. and Smith, D. (1979) ‘Growth and survival studies of psychrophilic and mesophilic yeasts’,
Microbios., 99(25).
• Temperature classification (no date) Available at:
http://iws2.collin.edu/dcain/CCCCD%20Micro/temperatureclassification.htm (Accessed: 27 January 2016).
• The Accidental Scientist (no date) Science of bread: Yeast-air balloons activity. Available at:
https://www.exploratorium.edu/cooking/bread/activity-yeast.html (Accessed: 20 January 2016).
• Volk, T. (no date) Saccharomyces cerevisiae, bakers’ and brewers' yeast. Tom Volk's fungus of the month for
December 2002. Available at: http://botit.botany.wisc.edu/toms_fungi/dec2002.html (Accessed: 27 January
2016).