The storage bag includes an interior volume for containing food items and a one-way valve element through which air from the interior volume can be evacuated. To prevent fluids and juices from the stored food items from contaminating the valve element, a separator defining a chamber is included that sealingly connects the valve element to the interior volume. In the separator, fluids and juices separate from the evacuating air by gravitational separation and are returned to the interior volume. In an embodiment, to facilitate packaging and distribution of multiple storage bags, the separator is adjustable between an expanded position for providing the chamber and a collapsed position substantially eliminating the chamber. In an embodiment, the separator may be comprised of elastically expandable material.