Choose broccoli with firm, tight dark green florets. The stalks should be slightly lighter in color. Yellowing broccoli is old and will taste overly strong; a whitish stalk will be tough and woody. Refrigerate broccoli in a plastic bag up to five days. Separate the head into florets to encourage even cooking. Peel and slice the stems and cook them along with the florets. Broccoli is best roasted, sautéed, steamed, or blanched.