This plan is for the minimum classroom situation or even a science fair type project at home. If your school has more sophisticated supplies such as a pH meter, an autoclave, and laboratory glass and plastic ware, feel free to create a more elaborate protocol.
Small jars such as baby food jars boiled along with their lids and then dried upside down and stored with lids on (This is sterile enough.)
Plastic, disposable, sterile (enough) urinalysis cups with lids purchased from the pharmacy.
Small, clear plastic, disposable drinking cups covered with saran wrap (if both are fresh from the package they are sterile enough).
Use it right from a freshly opened container of whole milk.
Note: For those who have a microbiology course in their background and who recognize this as the famous “litmus milk test,” please feel free to actually do the “litmus milk test” if you have all the supplies and equipment on hand.
The pH paper:
This is a common item in even the most minimum science lab. Alternatively, purchase some urinalysis test strips at the pharmacy. In addition to testing pH, these will do some other assays too. It might be fun to try to interpret the other tests. And an alternative to that is not testing pH at all.
Concerning the choice of bacteria:
You will add bacteria to milk. You will need to think ahead of time about what items to have on hand from which to get bacteria. These experiments will tend to favor lactic acid bacteria of the sort that are routinely consumed in yoghurt.
Sources of bacteria:
Discarding the Experiments and Other Safety Concerns:
Some of the results of experiments will look and smell edible. For example, when you add yoghurt to milk, you will get yoghurt. However, it is considered to be a bad practice to eat anything at all in a microbiology lab so refrain from doing that!
Students with compromised immune systems (either from drug therapies or diseases) should seek advice from their doctors before participating in this exercise or in any project involving bacteria or fungi. If they are allowed to be present, it should probably be as observers in a group rather than handling the experiments directly.
Of great concern in any classroom is how to discard the finished experiments from microbiology classes. For these experiments, use modest amounts of milk so there will be less to throw away. Then, throw it away in a plastic lined trash can, quickly tied up and brought out to the dumpster!