Caitlin Ward, Jessica Craik, and Anna McCaughan of Balclutha Primary School asks :-

Can you make bread without yeast, what if your yeast is out of date and what makes bread go mouldy?

Nigel Larsen, a food chemist, and Ian Waters, a baking technologist, of Crop and Food Research, responded.

Yes, there are several ways to make bread without adding yeast but most people like the taste of bread made with yeast.

You can make dough and hope that yeasts that are floating around in the air will settle on it and start to grow. This takes longer, so dough made without adding yeast takes much longer to rise.

People (like my grandmother) used to put aside a small piece of dough each day as a ‘starter’ to add to the dough they made the next day. A few bread recipes, like potato bread, are made using baking soda to produce the gas bubbles instead of yeast.

Another way is to make ‘sour dough bread’. This bread uses special ‘good’ kinds of bacteria to produce bread that tastes different from normal yeast bread.

For yeast to work properly in bread dough it needs to contain live yeast cells. After you mix bread dough the yeast cells start to grow. If the yeast is old or has been kept too hot some of the yeast cells will be dead. So the yeast won’t produce enough gas bubbles and the dough won’t rise much or very slowly.

Moulds and yeasts are always floating around in the air so when we open a loaf of bread some of them settle on the bread. Bread is a very nice food for moulds. They will soon start to grow if we don’t eat it first! Moulds grow fastest on bread if it is warm and moist.

Moulds won’t grow on bread if it’s too dry but we don’t like dry bread either. If we put our bread in the fridge to stop the moulds growing, it goes stale and doesn’t taste nice. So it’s best to eat bread while it’s fresh or put it in the freezer so you can use it when you need it.

If you want to read more about baking bread and the baking industry in New Zealand, check out the website at