Food: Science Picture Challenge #2 Dead or Alive?

When I first started out learning to bake bread from cookery books, my bread was always flat and as hard as rock. That was until I learnt one simple but crucial trick - testing the yeast to see if it is still alive.

If you use dead yeast to make bread it won't rise, so you should test to see if the yeast is alive. Activate it with some warm water and a pinch of sugar and in about ten minutes time it should start to bubble.

So exactly how does the yeast work in bread making? According to one of my favourite baking website

As bread dough is mixed and kneaded, millions of air bubbles are trapped and dispersed throughout the dough. Meanwhile, the yeast in the dough metabolizes the starches and sugars in the flour, turning them into alcohol and carbon dioxide gas. This gas inflates the network of air bubbles, causing the bread to rise. During rising, the yeast divides and multiplies, producing more carbon dioxide. As long as there is ample air and food (carbohydrates) in the dough, the yeast will multiply until its activity is stopped by the oven’s heat.

Here's my dough after is has been mixed and kneaded. Thanks to the yeast, you can see how much is has risen within two hours.

Now I have shaped my bread rolls and the yeast is still busy working hard.

Now I just need to wait for 20 minutes before I can dig into freshly baked bread.