Oatmeal is used as a breakfast cereal and in breads, granola mixes and cookies. It is a staple food usually stored in a cupboard or pantry. Manufacturer expiration dates of oatmeal will vary, making it difficult to determine how long you can keep that container of oatmeal around. Airtight containers will keep moisture out of oatmeal, prolonging its shelf life.
The Texas Agricultural Service of Texas A&M University recommends storing ready-to-cook oatmeal in a cool and dry place for up to 12 months. If the oatmeal container is opened, the remaining oatmeal should be placed in an airtight container in a cool and dry storage place where it will keep for up to 12 months as well. Any type of moisture will cause dry oatmeal to go bad.
A long-term storage oatmeal study, published in the "Food Science Journal" in 2006, found that oatmeal stored for up to 28 years in a reduced oxygen atmosphere and at room temperature retained many of its nutrients. Vitamin B-1 content was between 2.7 and 6.6 micrograms per gram of cooked oatmeal, with some of the highest vitamin B-1 content in the oldest samples. Vitamin E amounts were between 1.3 and 37.8 micrograms per gram of cooked oatmeal, depending on the chemicals in the air stored in the container along with the oats.
The 2006 study published in the "Food Science Journal" found that oatmeal stored for up to 28 years in a reduced oxygen atmosphere and at room temperature was still edible from an aesthetic standpoint. They cooked 16 samples of quick-cooking and regular oatmeal and asked panelists to judge how edible the samples were. Three-quarters of the panelists rated the samples good enough to be used as emergency provisions.
The University of Virginia Cooperative Extension recommends that all cooked foods be thrown away if they have been sitting out for more than two hours. The "Star Tribune" "Master Oatmeal Recipe" claims that you can store cooked oatmeal from this recipe in an airtight container for up to seven days. The "Star Tribune" recommends that if you are not going to eat the oatmeal right away, store any cooked fruit mixtures separately in the refrigerator in an airtight container until you are ready to add them to the oatmeal. These fruit mixtures will last up to two weeks.