As vegetable gardeners we know all too well how fast the optimal qualities of fresh produce vanish. Sweet corn, peas, green beans, lettuce -- even Brussels sprouts -- lose their peak flavor soon after picking. But perfect asparagus may be the most ephemeral vegetable of all. Not only does it lose its sweetness and most delicate flavor very soon after picking, but it gets noticeably tougher within a few hours.
According to research by Marita Cantwell and others at the University of California at Davis, asparagus became significantly harder to slice within four hours of harvest if left at room temperature.
The researchers measured the increased toughness along the centers of 10" spears. The toughening begins toward the base of the spear and is most pronounced there. Sugars are also concentrated at the base, so when you trim away the bottoms, you lose the sweetest portion.
To preserve its quality, refrigerate asparagus as soon as you cut it from the bed and keep it there until you are ready to cook or freeze it. Bundles should be relatively small so that interior spears can cool promptly.