Maps, Photographs and Words

The Salmon's Return

A salmon hatches in a river, swims to the sea, and comes back years later to the river it was born in. It finds its way home by smell. Every river carries its own mixture of soil, rock and plants, and a young salmon learns that smell before it leaves. The return journey is upstream. The fish leap waterfalls, sometimes several metres high, and they do not eat once they enter fresh water. Because it is not feeding, a salmon uses up its own body on the climb. By the time it reaches the gravel where it hatched, it is thin and worn. There it lays its eggs. Most Atlantic salmon die soon afterwards.

Why Bread Rises

Yeast is alive. It is a fungus, and each grain of dried yeast holds millions of cells waiting for water. Add warm water and the cells wake up. They begin to feed on the sugars in the flour. As they feed, they give off carbon dioxide gas. The gas cannot escape, because kneading the dough has built a stretchy web of gluten that traps it. Thousands of tiny bubbles form, and the dough swells. In the oven, two things happen. The trapped gas expands in the heat, so the loaf rises further. Then the heat kills the yeast and sets the gluten, and the bubbles are locked in place. That is why bread has holes in it.