Bread making depends on the activities of micro-organisms. It is an ancient craft but in the 21st century bread making has been transformed into an industrial process allowing controlled production on a large scale with a more predictable final product. However in many cultures and families bread is still made using traditional methods.

The dry ingredients used in bread-making include flour, usually from wheat, salt, sugar, ascorbic acid and the yeast Saccharomyces cerevisiae. Water or milk is added to produce a thick, sticky dough which is folded repeatedly or kneaded. This dough is rested, folded again then shaped into tins. The dough is left to "prove" in a humid atmosphere at approximately 35° Celsius. It is then reshaped and left to "prove" some more.

During the "proving" process, fermentation of sugars in the dough, catalysed by enzymes from the yeast cells, produces carbon dioxide.

The series of reactions that occur with the help of enzymes from yeast are:

	maltese from yeast
a) Maltose in flour		produces glucose
	invertase from yeast
b) Sucrose from added sugar		produces glucose + fructose
	zymase from yeast
Fermentation reaction: c) Glucose + fructose from previous reactions		produce alcohol + carbon dioxide

The production of carbon dioxide is needed to make the dough rise, or increase in volume. This process is called leavening. Adding ascorbic acid (vitamin C) makes the dough more elastic and better at trapping gases and as a result reduces the time required for leavening, which is an important consideration in commercial bread production. The overall effects of leavening are to make the dough lighter, more easily digested and with better flavour, enhanced by the production of organic acids, alcohols and esters by yeast cells.

Baking evaporates off any alcohol and inactivates the yeast. It also causes bubbles of carbon dioxide to move through the dough, giving the bread a spongy texture after baking.

Biotechnologists are currently attempting to improve strains of yeast used in bread-making, aiming to produce more active, better flavoured strains which can make dough rise at lower temperatures, and in less time.

Activities:

1.	Students develop a glossary of new terms used in the article: ascorbic acid; yeast; Saccharomyces cerevisiae; kneading; proving; catalyst; enzymes; carbon dioxide; fermentation; leavening; alcohol; biotechnologists.
2.	Discuss the importance of yeast in the bread-making process.
3.	Investigate other food and beverage industries, which use processes dependent on activities of micro-organisms.
4.	Use a bread maker machine to bake a loaf.

Need assistance? Explore these websites…

»	Science of Cooking Bread www.exploratorium.edu/cooking/bread/ then click on 'Slice-O-Scope' or 'Explore Gluten'
»	Bread-making - Tip Top Bakeries www.tiptop.com.au then click on 'virtual bakery'
»	Cheese, Butter & Dairy Farming - Australian Dairy www.dairy.com.au then click on 'kids & students'
»	Yoghurt - Paul's; www.pauls.com.au click on 'Information Centre' and then click on 'Probiotics' or ' Glossary of Terms' - Yoghurt activity on LandLearn website; http://www.landlearn.net.au/curriculum/ classroom_activities/making_yoghurt.htm
»	Health drinks Yakult Australia; www.yakult.com.au then click on "Education"

Resources:
For Further Information about bread and recipes:

»	History of bread-making - Australian Wheat Board; www.awb.com.au then choose items from the 'Community Education' drop down menu
»	Exploring health issues in populations - Devondale; www.devondale.com.au then click on 'Health and Nutrition' to learn about Calcium - Nestle Australia; www.nestle.com.au then select the 'Food & Nutrition' drop down menu and click on 'Nutrition'
»	Micro - organisms in Action - Peter Freeland Hodder & Stoughton, 1991
»	Wheat Kit - The Workboot Series - Kondinin Group, 1997