Where does bread come from, and where does it go after we eat it?

In numbers

• ≈ 14,400 yearsage of the oldest known bread
• ≈ 10,000 yearssince einkorn wheat was domesticated

In five stops

1. 1

   Where were its atoms born?

   Bread is mostly starch: carbon, hydrogen and oxygen. The hydrogen atoms are left over from the Big Bang; the carbon and oxygen formed inside stars. The nitrogen in its proteins was also born in stars. These atoms joined our planet when Earth formed and have been moving through the air, water and soil ever since.

2. 2

   How did nature prepare it?

   Wheat takes carbon dioxide from the air through its leaves and water from the soil through its roots. In photosynthesis it uses the Sun's energy to turn them into sugar, and then into starch stored in the grain. The nitrogen for its proteins comes from the soil. So a grain of wheat is packaged sunlight, made largely out of air and water.

3. 3

   What did people do?

   The oldest known bread remains were made about 14,400 years ago in Jordan, from wild cereals, before farming even began. Einkorn wheat was domesticated a few thousand years later, about 10,000 years ago, in the Fertile Crescent. Today flour is kneaded with water, leavened and baked. Yeast feeds on the sugars in the flour and releases carbon dioxide; those gas bubbles make the dough rise. The browning of the crust in the oven is called the Maillard reaction.

4. 4

   What happens when we use it?

   During digestion, starch is broken down into glucose and passes into the blood. Our cells burn the glucose with the oxygen we breathe in, and the energy released lets us move, think and stay warm. It is a slow, controlled burning, without a flame.

5. 5

   Where does it go next?

   Glucose's carbon atoms leave in our breath as carbon dioxide, and its hydrogen atoms leave as water in our breath, sweat and urine. The nitrogen from proteins leaves in urine, and some atoms become part of our body for a while. The carbon dioxide we breathe out may one day be taken up by another plant: bread's atoms travel in a cycle.