Place the baking soda into a small oven-proof dish.
Bake the baking soda for 1 hour.
Remove the dish from the oven.
Let the baking soda cool completely.
Carefully transfer the baking soda to a sterilised glass jar. Take care not to touch the baked baking soda with your bare hands as it may irritate the skin.
To Make the Lye Water
Make the lye water just before you need to use it.
To make lye water for use in most recipes, you need to use a ratio of 1:4, i.e. 1 part baked baking soda to 4 parts water.
So for 1 teaspoon of lye water, mix 1/4 teaspoon baked baking soda with 1 teaspoon water.
Any unused lye water can be discarded down the kitchen drain.
Kitchen Notes
HOW MUCH BAKING SODA TO USE If you need to use lye water only occasionally, I recommend baking about 1/2 cup of baking soda at a time and storing it in a glass jar or glass spice jar. The baked baking soda keeps fairly well indefinitely in a sterilised jar, but make sure you label it accordingly.
OVEN TEMPERATURES All recipes on this website state temperatures for a regular oven (i.e. a conventional oven without fan). If you have a convection oven with a fan, please consult the manufacturer's handbook on how to adjust the temperature and baking time accordingly.