Boil 12 ounces of water with the electric kettle. Every electric kettle has a different amount of time needed to heat the water to boiling, so refer to the instructional manual for how long this will take.
Place two ounces of loose-leaf tea leaves into a teapot, then pour six ounces of water (half of what is in the electric kettle) over the tea.
Set your timer to 30 seconds. Wait for the time to elapse, then pour the teapot's contents through the sifting sieve and into the other teapot. The tea leaves will be separated from the first brewing, and the liquid will contain the caffeinated contents.
Place the tea leaves back into the empty teapot, then pour the boiling water that remains in the electric kettle back into it. Allow the tea leaves to steep for the amount of time specified on their packaging, which is usually five to 10 minutes.
Empty the teapot containing the caffeinated first brew, then pour the second teapot's contents into it. Hold the sifting sieve in between the two teapots to separate the leaves from the liquid.
Place the D+Caf test strip into the teapot containing the second brew, then remove it and see what percentage of caffeine remains in the tea. The reading will indicate that the tea contains around 20 percent of caffeinated content, which is the exact amount for the tea to be considered decaffeinated. Read your D+Caf test strip's instructions for the amount of time needed to get accurate results, as test strips differ by manufacturer.