a sterilization apparatus includes a housing adapted for receiving a removable rack with open shelves supporting containers with the substance to be sterilized , a fan arranged at the top of the housing , and a cooling device for subsequent cooling of the sterilizing fluid introduced into the housing . to increase the uniformity of whirling of the fluid around the containers on different levels of the rack and thus to increase the heat transfer to , and the subsequent heat removal from the containers , a timing - and flow - controlling device is provided for cyclically changing the flow of the sterilizing fluid through the rack during the heating - up and cooling - down of the sterilization cycle , either by alternating the direction of the flow , or by distributing periodically partial streams through different shelves of the rack .