Gather your ingredients so that you have everything close at hand on the counter or table.
In a large saucepan, boil water and add oil. You may also add food coloring at this time if you only desire one color.
Remove from heat and add the peppermint flavoring for scent. Stir in the all-purpose flour, salt, and alum. Mix well, using a long-handled wooden spoon.
When the dough is cool enough to work with, you may divide the dough into separate bowls. One for each color.
Work each color in by kneading the dough with your hands. (You may want to use plastic gloves to protect your hands from food coloring.)
Place in covered container and refrigerate. This playdough recipe will stay fresh in the refrigerator for several months. Makes 4 large of playdough.