A thin, flexible stem indicates a tender, young plant. Choose these spinach leaves for salads or recipes where the spinach is served raw. Thick, fibrous stems mean more mature, tougher plants, which are best suited for cooking.
Shop for crisp, bright green leaves with no dark, bruised patches or yellowing. I like to buy loose leaves or bunches so I can judge their quality. Store fresh spinach in a dry plastic bag in the refrigerator crisper, where it will keep for two to three days.