Baked goods should usually be stored in airtight containers to give them the longest shelf life and keep things from becoming stale. Airtight containers will keep cookies crisp and chewy and keep cakes moist and fresh tasting much longer than simply leaving them out on the counter.
During the summer, however, keeping your baked desserts in an airtight container can actually create some unexpected problems, particularly for moist baked goods like cakes, cupcakes and quick breads. If your kitchen gets too hot, heat can start to build up inside the container and your cake can start to “sweat” out the moisture inside. You might actually start to see some steam building up within your storage container! If left this way, you will end up with a cake that starts to get soggy around the edges, as well as a cake that will begin to spoil quickly due to the warm, bacteria-friendly environment inside the hot container.
The best thing to do during the summer is to try to keep the heat away from your cakes and cupcakes, storing them in a cool place out of the sunlight. You can also prevent heat from getting trapped around your baked goods by keeping your storage container – whether it is a ziploc bag or a hard-sided carrying case – cracked open to allow for some airflow. If you are dealing with very extreme heat, or need to transport your goodies somewhere and they’ll be exposed to the sun, you can stick them in the refrigerator in their airtight container. Usually the refrigerator will dry out baked goods and may cause them to stale quickly, but it will cool them down enough to survive a trip to a summertime picnic and will preserve them better (and keep that frosting from melting!) than being left out in the heat.