The rhubarb plant is botanically a perennial vegetable, though it is often treated as a fruit in cooking due to its distinctly tart flavor. The plant is characterized by large leaves atop thick, fleshy stalks. Understanding which part of the rhubarb is safe to consume is paramount, as the plant contains a natural compound that is toxic at high concentrations. Caution is advised when harvesting or purchasing the plant.
Identifying the Safe Portion
The only part of the rhubarb plant that is safe for consumption is the stalk, also known as the petiole. Stalks are used extensively in desserts like pies, crumbles, and jams, valued for their unique sour taste that balances well with sugar. When selecting fresh rhubarb, look for stalks that are firm, crisp, and unbent, indicating freshness and quality. Before cooking, the ends should be trimmed, and the entire surface washed to remove any soil or residue.
Rhubarb stalks range in color from deep crimson red to speckled pink-green, or entirely green, depending on the specific cultivar. This variation is caused by the presence of pigments called anthocyanins and is not an indicator of the stalk’s edibility or sweetness. Both red and green stalks are safe to eat, though many cooks prefer red varieties for the vibrant color they lend to finished dishes. The plant’s tough, fibrous texture softens considerably when cooked.
Identifying the Toxic Portion
The large, fan-shaped leaves of the rhubarb plant are poisonous and should never be consumed. These leaves must be completely removed and discarded immediately after harvesting the stalks. The leaves contain a highly concentrated toxic compound that makes them dangerous to humans and animals. They should not be allowed to accidentally contact food preparation surfaces or other edible ingredients.
Cooking, drying, or any other form of processing does not neutralize the toxic elements in the leaves. The harmful compound remains stable and potent even after exposure to high temperatures. Therefore, the leaves must be composted or discarded entirely, ensuring they are kept away from all food sources. This separation is a necessary safety protocol to prevent accidental ingestion.
The Science Behind the Danger
The primary toxic agent in rhubarb leaves is oxalic acid, a naturally occurring compound found in various plants, though at much lower levels in most edible vegetables. The concentration of oxalic acid in the leaves is significantly higher than in the stalks, which is why the leaves are unsafe to eat. Once ingested, oxalic acid acts as an anti-nutrient by binding with calcium in the body, forming insoluble crystals of calcium oxalate. This binding process removes free calcium from the bloodstream and can interfere with the body’s normal calcium metabolism.
The formation of calcium oxalate crystals is particularly damaging to the kidneys, where these sharp, microscopic formations can accumulate. This accumulation can lead to the development of kidney stones and, in severe cases of poisoning, result in acute kidney failure. Symptoms of rhubarb leaf poisoning can range from mild gastrointestinal distress, such as nausea, vomiting, and abdominal pain, to more severe systemic effects. Serious toxicity can manifest as a burning sensation in the mouth and throat, difficulty swallowing, muscle cramps, and convulsions. Anyone who suspects accidental ingestion of rhubarb leaves should immediately contact a poison control center or seek emergency medical attention.