Wash spinach, making sure you discard any wilted and brown leaves.
Fill a large bowl with cold water. Add a bunch of ice cubes to the water and set aside. You need your water to be ice cold.
Boil a kettle (about 3-4 l of water, so you may need to boil it a couple of times).
Add spinach to a large colander and place in a sink. Pour the boiling water over the spinach slowly, making sure to get all the spinach to wilt. Use more boiling water if needed. Leave the wilted spinach for 2 minutes.
Using tongs, place the wilted spinach into the bowl with ice water and chill for 3 minutes.
Drain the spinach. Using your hands form small balls of spinach squeezing any extra moisture out.
Lay the balls out on a chopping board or a baking tray in a single layer and pop them in a freezer for 2-3 hours. Once frozen, transfer to freezer-freindly ziplock bags.
Use within 4-5 months.