Swiss Chard, and other leafy greens, have high levels of oxalates which can cause problems by forming stones in our body, especially in our kidneys. Since oxalates are water soluble, the blanching of leafy greens like swiss chard, spinach and beet greens is recommended before eating.
I’ve tried to research whether dehydrating removes oxalates and have not found any evidence that it does. I would suspect that since only H2O is evaporated from the vegetable, the oxalates would be even more concentrated in the dried greens. Can a healthy person consume small amounts of high oxalic foods without problems? Probably.
When I dehydrate swiss chard, I choose to first blanch the leaves. I remove the center rib of the chard and cut the leaves into approximately 4″ pieces. I blanch in boiling water for a minute or so. I then drain the chard and discard the water. I lay the leaves in a single layer on a parchment covered cookie sheet and place in my oven which has been heated to 150 degrees.
I check the progress every hour until the leaves are dry and crumble easily. When they are completely cool, I store them in an airtight container for use in soups and stews throughout the winter.