As a teenager I learned about sorrel and decided to grow it from the Sunset book How to Grow Herbs (1972). It says dismissively: “Sorrel was once eaten as a vegetable, prepared in the same fashion spinach is today and as a green in salads.”
Perhaps the note of suspicion relates to sorrel’s oxalic acid content, though the book makes no mention of it. This organic compound, also produced by our own bodies, can be toxic in large quantities. This is what makes rhubarb leaves poisonous. In particular it is noted for binding calcium and iron, preventing intestinal absorption of these essential minerals, and for producing kidney stones. Eat That Weed provides a good discussion of the cautions around oxalic acid and how foragers can minimize its effects. Note that many spring greens, rhubarb stems, purslane and even spinach contain similar or higher levels of oxalic acid.
We might be tempted to eat too much this time of year. The deep roots provide a healthy crop of leaves that is quickly replenished. From our garden, despite an early April harvest by the groundhog, we have already had one meal from my single vigorous plant. The photo shows it is ready again. Sorrel is also readily available at the farmers’ market. I approach the nutritional issue simply by neither eating it too often nor in large quantities.
Thanks to the oxalic acid, sorrel has a delightfully sour taste, a bit like spinach but more lemony. It might be compared to kiwifruit. Try substituting it in a recipe for spinach squares. As a teenage herb gardener I used to make sorrel soup by sautéeing a handful of spinach in 2 tablespoons of butter, stirring in 3 tablespoons of cream and cooking until thick, then adding 3 cups of chicken stock and heating gently. It can also be used (instead of basil) in a spring pesto, which may be the best way of extending the flavour of a few leaves.