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|Homemade Petri Plates and Media|
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Homemade Petri Dishes
Look around your kitchen and you might find a set of custard dishes, preferably without stems. These will make very good petri dishes when covered with a double thickness of aluminum foil. You will want to half-fill them with your homemade nutrient agar. For future reference measure the half-volume of one of them.
Homemade Nutrient Agar
You need to purchase some cans of either beef or chicken consumé soup. These are essentially "nutrient broth" in event you need liquid medium for an experiment.
From a health foods store, purchase some agar (or agar-agar).
To a sauce pan, measure out the amount of consumé, and then weigh out some agar powder to that the consumé will be about 2 percent in agar (2 grams of agar per 100 ml of consumé). (Yes, you would be doing yourself a favor by obtaining a metric set of kitchen measuring equipment. While not common in North America, they are used elsewhere in the world, and thus produced in huge quantities. Your kitchen supply store will probably have some so that immigrants can use their former cookbooks.)
With constant stirring, bring the mix to a boil and stir continuously for an additional minute or two to dissolve the particles of agar. Remove from the heat.
Pour your hot mix into the custard dishes so that each is about half full.
Cover each dish with a double layer of aluminum foil, and be sure that the apron of the foil hangs down at least a half-inch (1 cm) from the dishes' tops.
Load you dishes carefully into your home pressure cooker. You may need to place a supporting rack atop the bottom layer of dishes to support another layer. Such racks can be made of rigid 1/4 inch hardware cloth cut in circles to fit your pressure cooker.
Click this for instructions on how to use a pressure cooker.
Once the dishes and media have been sterilized, you may allow them to sit until they gel. (In event that they do not gel, you will have to add more agar powder, as that which you purchased was not pure and was diluted with some sort of non-gelling filler.)
AND THERE YOU HAVE IT! You now appreciate having commercially prepared media!
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