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A simple experiment to demonstrate the effect of temperature on fermentation by yeast


Apparatus and Materials


Waterbaths
set to a range of suitable values - chosen from 25, 30, 35, 40, 45, 50, 55, 60 C
(in addition to room temperature 15 - 20 C ?)
thermometers

Beakers:
1 large (1000 ml ?) for mixing - preferably marked on side
(10 x) 100 ml beakers
(10 or 20 x) 10 ml measuring cylinders
rubber bungs to fit above
forceps
Materials (sufficient for 10-12 treatments):
800 ml (red?) grape juice (UHT is OK)
100 ml yeast suspension (ready prepared)
[5g sucrose, 15g dried yeast, 125 ml water - mixed in 500ml beaker & incubated at 30 C for 30-120 minutes before use]
plastic rod for mixing

Method


Measure out the grape juice into the large beaker using markings on the side of the beaker as a rough guide.
Mix the yeast suspension using the plastic rod, and add the yeast suspension to the grape juice (quantities not critical - no need to worry about froth!).
Mixing each time using the rod, pour about 75 ml of the mixture into each smaller beaker, and place each into a water bath to come to its operating temperature.
Check that the water level in the waterbath is deep enough to cover the contents of the beaker, but not enough for it to float and possibly capsize.

After say 5 minutes, pour the mixture into a measuring cylinder, so as to completely fill it, not just to the top of the measurement lines. Holding the measuring cylinder over a tray or beaker, lightly insert the rubber bung. Some overflow must be expected!

PourSeal



Invert the measuring cylinder in the beaker and replace it in the water bath.

Using forceps, remove the bung, ensuring that mouth of the measuring cylinder is still under the liquid. Note the time.

InvertForcepsUnsealRemove bung



Repeat the process for the other temperatures.

It is possible to get more than one measuring cylinder in a beaker at one time, and to remove and re-use the same rubber bung.

Record the results (level of gas - read with measuring cylinder held vertical) at regular intervals - say every 5 or 10 minutes. Remember that the scale is upside down and there will be a point at which the gas level is below the scale markings. You may need to estimate the value or reset by re-filling the measuring cylinder and keeping a running total.

Gas



Time
/min
Volume of gas at the following temperatures:
/ml
. 1520 2530 3540 4550 5560
/ C
0               
5              
10              
15              
20              
25              
30              
35              
40              
45              
50              

Although easily criticised, this experiment usually works well in a double lesson and usually gives a clear optimum temperature.


In practice, it is easier to set up than this theoretical experimental setup (from an exam paper)!
Yeast tubes (theoretical) experiment

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