Let the pieces of cardoon fall into a bowl as you cut, and immediately squeeze fresh lemon juice over the pieces. Toss the pieces in the juice to coat them well.
Peeled cardoon turns brown very quickly, and a generous amount of lemon juice will counter the oxidation process so that the stalks remain green until cooking time. You can also use vinegar if you don't have lemon juice.
Repeat the entire paring process – from removing the leaves and prickers to paring the strings and skin – with the remaining stalks of cardoon.
The thin, whitish, young stalks covered with soft leaves are good to use as well. They're also easier to clean – just scrape off the white coating.
