Be sure you squeeze lemon juice on the cardoon every time you add a cut stalk to the bowl.
This cardoon is ready to cook. I covered it tightly with plastic wrap and stored it in the fridge for four days before cooking it. It kept perfectly, and didn't turn brown at all.
The cardoon will stay a beautiful green color as long as only an acidic liquid, like lemon juice or vinegar, touches it. Submerging cardoon in water with vinegar doesn't keep it nearly as fresh as plain lemon juice.
Keep the cardoon covered tightly, and wash it only when you're ready to add it to your pot for cooking.
