Method
Firstly we drew in different amounts of each substance respectively into each syringe to different ratios detailed in the results table below and squirted each substance into two test tubes, each substance in its own test tube. Then we put both test tubes into the water bath and started the stopwatch measuring the temperatures of each substance at regular intervals. When the temperature of both substances were the same as the temperature in the water bath we stopped the stopwatch, recorded the results and proceeded to mix the rennin with the milk, started the stopwatch again and placed the test tube back into the water bath. At regular intervals we took the test tube out of the water bath and checked to see if the milk had clotted, we decided it had clotted when the milk was quite solid and we would excuse a little milk running from it because we did not have enough time to wait for the milk to clot fully. When the milk had clotted we stopped the stopwatch and recorded the results, we repeated this whole process three times in a 30’C water bath each time using different ratios of milk and rennin to see what ratio was best for the main experiment.
Results
These results tell me the ratio 2:1 for milk and rennin respectively (The third one down) is the best ratio because the milk clots much quicker than the other ratios. This is because the milk only needs the rennin to speed up the reaction, the milk would clot without the rennin so the milk only needs a helping hand to clot quickly. We will use this ratio because we do not have much time to carry out the main experiment and also the cheese makers would want the milk to clot in the quickest time possible so as to make the cheese quicker so it would be more realistic to use the quickest reaction time possible.
Main Experiment
Method
This experiment is very similar to the experiment we carried out before to find the most suitable volume to use except the variable we are changing is the temperature not the volume but we are again measuring the time taken for the milk to clot.
For the main experiment to find out what the relationship is between temperature and the speed of the clotting reaction we will need to use a variety of apparatus:-
- Water bath x5
- Test tubes
- Syringes x2
- Stopwatches x4
- Thermometer x2
- Safety glasses
- Rennin
- Milk
This investigation should be carried out safely because we’ll be wearing safety glasses to protect our eyes from any rennin or milk getting into them and the water is not hot enough to burn. To keep the experiment fair, the only variable we’ll change is the temperature of the water bath, we’ll not change the volume of each substance (milk 2cm and rennin 1cm) or anything else.
Firstly we set up the apparatus by heating each of the 5 water baths to their temperatures, we have decided to use the temperatures 30’C, 35’C, 40’C, 45’C 50’C and 55’C,(range 30’C-55’C). Because there is a 25’C difference between the lowest and highest temperature and so there’ll be quite a difference in the results. Then using the syringes, we measured 2cm of milk and squirted the milk into a test tube and using a different syringe so as to not to mix the substances we measured 1cm of rennin and squirted that into a test tube, then we put both test tubes into a water bath. We used a thermometer to measure at regular intervals the temperature of each substance, like the syringes, we used a different thermometer for each substance. When the substances were both the same temperature as the water bath (in the first water bath 30’C) and each other we added the rennin to the milk and started the stop watch, replacing the test tube with the milk and rennin to maintain its temperature in the water bath. We then waited picking up the test tube at regular intervals and checking to see if the milk had clotted, we decided the milk had clotted if most of it was quite solid and with maybe a little milk running off it. We decided to excuse a bit of milk running out of the test tube because we did not have enough time to wait until the milk had fully clotted.
When the milk had clotted we stopped the stopwatch and recorded the time the milk had taken to clot. We carried out this experiment three times in the same temperature to keep the experiment fair and so we could get three sets of results, get an average and compare results to make sure the results were not overly inaccurate or incorrect. Next we carried out the same experiments in the other water baths, recording the actual temperature of the water bath using a thermometer because the actual temperature of the water bath could be different from what we presume and also the time it takes for the milk to clot.
Results
I don’t think we had to record more than three sets of results because it’s enough to make an average. There’d be no point in using any higher temperatures because if the rennin molecules denatured at 55’C then the molecules would do the same at a higher temperature. I’m glad we recorded the actual temperature of the water bath instead of just taking for granted that the temperature written on the side of the water bath was correct.
Looking at these results I realise my prediction was correct, you can see that the colder the reactants the slower the reaction takes place for the milk to clot because the enzyme molecules are moving around slowly with much less successful collisions with other molecules. But the warmer the two substances, the quicker the reaction, compare the 30’C results with the 40’C results and this proves my point, the reaction took much less time at 40’C than at 30’C. This is because the protein molecules in the enzyme rennin are moving about much quicker because they’ve got more kinetic energy from the heat, with many more successful collisions and so the reaction is going to be faster than at a lower temperature. At 55’C the molecules denatured and so no reaction could take place, the physical shape of the protein molecules in the rennin has changed which means at this heat a reaction cannot take place because the “Lock and Key” theory comes into play which I have detailed about in my prediction. To improve the experiment I would try and get more accurate results because in theory if you have the same volume of both substances and they are heated at the same temperature then you should get the same results. But look at the results table and the graph you can see that the reaction times are not the same which suggests two things:-
- The volumes were not measured accurate enough.
- The stopwatch was not stopped as soon as the milk has clotted, the milk could have been clotted for quite some time with out us noticing.
So as you can see I do not think our results were accurate enough and some results seemed totally wrong, the 2nd and 3rd results for 40’C and 50’C are over a minute more than the first time we did the experiment.
To improve this experiment I would try to measure the volumes as accurate as possible by having the measurements checked by several people instead of just having a quick look at the measurements as I did in this experiment. Also, next time I should check the milk more regularly to make sure I stop the stopwatch as soon as the milk is clotted instead of being a few seconds out like I was in this experiment. One last thing, I’d try to keep the temperature of the water bath at an accurate temperature, not a few Celsius out e.g. (30’C actual temp 28.5’C). Also I’d try to keep the temperature of the water bath constant because as time goes on the temperature of the water bath could change while we wait for the milk to clot.
Other investigations I could carry out to support or find out more about what we have done are:-
- Change the concentration of the rennin to see if the reaction time changes.
- Change the type of milk e.g. to full cream etc, to see if the reaction time changes.
- Change the ratios of the milk and rennin and carry out the same experiment again.
- Use different temperatures e.g. 20’C, 25’C, 60’C, 65’C etc to see if the temperature really does have a big impact on the speed of milk clotting..
Sion Brooks 10N