We recommend boiling only three of the World's Healthiest Foods—spinach, Swiss chard, and beet greens—to help reduce the oxalic acid found in these leafy greens.
Use a large pot (3 quart) with lots of water and bring to a rapid boil. Add spinach, Swiss chard, or beet greens to rapidly boiling water and boil uncovered. (The acid is released through the steam vapors as well as being leached into the boiling water.) After the water has returned to a boil, boil spinach for 1 minute and Swiss chard and beet greens for 3 minutes. Drain and press with a fork to remove excess water. We don't recommend using the boiling water for soup or for other cooking due to its acid content.