The Green Globe variety of artichoke is king in Castroville, California. Here are a few tips for choosing the freshest and best ones at your grocer.
They should be heavy when you heft them in the hand. Really fresh ones will make a rubbery squeak when you rub them together. The leaves (actually flower bracts) should be tightly packed and not loose or starting to open. The bottom bracts should break off smartly with a crisp snap and not be limp. The stem should look plump with firm skin, not wrinkled or dried out. If freshly picked, the stem end will still ooze a white milky sap. This sap darkens with exposure to air and the produce manager will often trim them again for appearances. If really fresh, some of the sap will still flow and the cut end will be tacky to the touch.
The best artichoke is the one and only one that grows up from the center of the plant. It will be the largest on the plant and have a thicker and broader heart (fleshy base) than other artichokes of the same size. This prime artichoke has a rounded crown, not a conical shape. The tips of the bracts usually point inwards. The link below shows two illustrations of artichokes. The upper photo of an artichoke field shows perfect prime artichokes. Again, note the globe-shaped crowns versus the lower photo of one of the lateral position artichokes with the pointy conical crown.
During the winter months, artichokes coming to market will often have frost bite, with some brownish scaling on the outer leaves. Not the most attractive appearance, but this does not affect the taste at all. Theres nothing wrong with these chokes and you shouldnt hesitate to buy them.