Banana stem typically has two types of layers. A hard inner layer which is edible. A porous outer layer which has to be discarded. Make a slit on the outer layer and remove it. You should be left with just the hard inner layer.

  

Use a peeler to gently scrape of some of the hard inedible portions of the inner layer.

  

Now slice the stem into circles. While cutting you will get a lot of thread like fibers sticking to the knife. Use your hand to pull those fibers apart and discard them.

  

Now chop of the circles into small cubes. Add the chopped banana stem to a bowl of water. Add a little bit of yogurt or lemon extract to the water and mix well, to prevent the banana stem from colorization. Keep immersed for 10 mins.

  

Take 2 small wooden sticks ( I used a wooden skewer), immerse it into the water and gently move it in a rotating motion. Once you pull out the stick outside, you will see some fiber sticking to the stick. Discard the fiber and repeat the process for a couple more times.

  

The banana stem is now ready to be turned into a delicious recipe.