Media may be dispensed in bottles with rubber-lined metal screw caps, polypropylene caps or tubes plugged with non-absorbent cotton wool. Small bottles may be sterilized with their caps screwed down firmly, but not packed tightly in the baskets. The larger bottles should have their caps loosened before heating and subsequently tightened for storage. A useful method of distinguishing between types of media is the use of colored non-absorbent cotton wool plugs in tubes or, in the case of bottles, colored caps or beads may be used.
Cotton wool plugs must not be so tight that air is excluded. On the other hand, they should be firm enough to allow one to raise each tube by its plug. Media for current use should always be stored in a dust-free cupboard or in a cool, moist atmosphere. For longer periods store at 4-6 degree Celsius. Each batch should be tested before use and labeled with a batch number. The shelf-life of media varies considerably. Poured plates will be used within a few days of preparation but agar slopes should be checked to ensure that moisture is still present. Supplies of the basal media should be such that each batch is renewed within 3 months of manufacture.
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