Ziploc brand bags are a staple in kitchens around the world. They come in different sizes for various needs, but the most familiar size is a sandwich bag. Ziploc bags tightly close with a zipper-like seal that locks out air from the food inside.
Foods prone to mold, such as bread, can have a longer shelf life when placed inside a Ziploc bag and properly sealed. Mold needs oxygen to grow; therefore, the more air removed from the bag the less likely mold will form. Ziploc bags also prevent airborne food spores from the food since they cannot penetrate the plastic bag. According to the S.C. Johnson and Son company, makers of Ziploc bags, the bags can be used to "freeze food, prevent freezer burn, defrost food, and to keep food fresher in the refrigerator, cupboard and on the go."
While Ziploc bags can keep foods fresher longer, they cannot stop mold from forming because mold spores are present on food before it is placed inside the bag. Ziploc bags can only help prolong freshness. Safe food handling procedures should always be followed no matter what type of bag or container food is stored.
Refrigerated foods keep fresher longer than food left at room temperature and freezing will stop mold from growing. Once frozen food is thawed the molding process will begin again because freezing does not kill the spores.