Conventional grapes, especially the imported ones, undergo heavy pesticides spraying; to avoid pesticides, choose organic grapes. Look for firm, plump grapes with a whitish bloom, which indicates the freshness. You can store grapes in the refrigerator for a few days in a plastic bag, but don’t wash them until just before you eat them. (excess moisture speeds spoilage). If you don’t plan to eat the whole bunch at once, snip off grape clusters with scissors rather than stripping the vine; this helps keep the remaining grapes from drying out. Chew them well to get the benefit of the skins, and if you find any seeds, eat those too.