This is the master stock for most traditional Japanese soups and many simmered or sauced dishes. The classic version of dashi is comprised of two ingredients —kombu (a sweet but sturdy kelp) and katsuo bushi (dried bonito flakes). Although it takes only a few minutes to make this subtle sea broth well, timing is crucial to success. If you allow the kelp to boil, your stock will become murky and bitter. And if you don’t strain the bonito flakes right away, your broth will taste fishy. The Japanese strain their stock through an all-purpose muslinlike fabric called sarashi. An old linen napkin or handkerchief, if you have one, is fine, but the disposable paper filters used in coffee makers are probably the most convenient. dashi loses its delicate aroma and subtle flavors when frozen, so it’s best to make it fresh when you need it. Any unused stock will keep well for 4 or 5 days in the refrigerator. Early signs of spoilage are clouding and a thick sediment at the bottom of the container.