Asparagus are very active-growing plant shoots. After harvest they quickly lose their sweetness and tenderness and develop a fibrous sheath from their cut end. White asparagus has a milder flavour than green and they toughen up faster. Buy asparagus as fresh as possible from the field, and store it in the coldest part of the fridge. Choose thick spears for the highest proportion of tender flesh to fibrous sheath. To restore some sweetness, soak asparagus for 1 hour in cold water with 1 to 2 teaspoons sugar per cup water and to minimise toughness, cut off the fibrous ends before cooking. To make use of the trimmed bottoms, slice into one millimeter thin rounds and serve raw on salads or add at the last minute to a soup or stir-fry.