Whether you can use oatmeal to make granola depends on your definition of oatmeal. Rolled oats -- also known as old-fashioned oats -- are sometimes called oatmeal, and are the preferred choice for making granola. Don't use the hot, creamy breakfast cereal, though, or you'll be left with a mushy, disappointing mess.
Oatmeal vs. Rolled Oats
The term oatmeal refers to a cooked porridge made from any type of oat. As the oats cook, they absorb water, and become soft and creamy. You can't use cooked oatmeal to make granola. The granola would be soft and bland, and lack its characteristic crunch. It would also spoil quickly without refrigeration. Rolled oats are sometimes called oatmeal. In this instance, you could certainly use "oatmeal" to make granola.
When making granola, you need a dry, thin oat that will remain shelf-stable after you slather the granola with a honey or maple syrup dressing and bake it. Steel cut oats -- also known as Irish oats -- are oat groats cut into many pieces. Steel cut oats cook slowly and retain a rough, chewy texture. They work best in cooked dishes. Old-fashioned -- or rolled oats -- are oat groats that have been rolled and steamed. This process doesn't alter the nutritional value of oats, but makes them cook more quickly. Rolled oats also tend to stay fresh longer because the oils in the oats are evenly distributed. These thin, dry oats are the ideal choice for granola. Quick oats are simply rolled oats rolled more thinly or steamed for a longer period of time. Quick oats are just as nutritious as rolled oats, but they cook rapidly and lack the slightly chewy, robust texture of rolled oats.
Whether you use rolled oats or quick oats, homemade granola is a cinch to make and can be highly economical, depending on the additional ingredients. Use rolled oats alone as the base for your granola, or combine them with flax seed, millet or wheat germ. Add nuts and seeds, such as pecans, cashews, flaked coconut, sunflower seeds or pumpkin seeds, as well as dried fruit. These added goodies taste delicious, but add calories and expense so use them sparingly. Toss the mixture with a combination of butter or oil and honey, maple syrup or brown sugar. Bake granola on a baking sheet just until it's golden brown and slightly crisp.
Heat It Up
Although you can't use cooked oatmeal to make granola, you can serve granola as a hot cereal. Simply add milk and heat in the microwave until warm. Granola also tastes delicious with fresh fruit or yogurt, or pack it dry for a quick and healthful snack.