If the size of the text in this page is too small, please either turn javascript on or adjust the default text size of your browser.
MV Home Scientists & Discovery home
Home Chemicals Reactions dna Lightning Rainbows Light Gravity Radioactivity Scientists

Bread

Every year, Australians eat an average of 44 kg of bread each.

Growing the wheat

Each grain of wheat is a tiny seed capable of growing into an entirely new wheat plant. Wheat plants use the Sun's energy to convert the chemicals in the air and the soil into the chemicals inside the seed that it needs to grow and survive. These include carbohydrates, fats and proteins. We also need these chemicals to survive. We eat plants such as wheat to obtain them because unlike plants we cannot use the Sun's energy to make them. Wheat and other plants also make many of the vitamins essential to our diet.

The roots of the plant absorb chemicals from the soil. These include water, minerals and chemicals from fertilisers and pesticides sprayed by the farmer. Fertilisers and pesticides are sometimes used to increase crop yield and prevent damage by pests. If these chemicals are present in the bread they are known as contaminants.

Producing the flour

The wheat is harvested and milled to produce flour. This breaks the grains of wheat into smaller pieces but does not change the chemicals in the wheat. Some of the chemicals are removed when pieces of the fibrous coating of the grain are sieved out to produce white flour.

Chemical additives are used to bleach and age the flour. Bleaching removes the chemicals that make the flour yellow. These chemicals are pigments called xanthophylls that occur naturally in wheat. They are also found naturally in potatoes and onions. Bleaching can also destroy the vitamin E in the flour. Ageing changes the structure of the proteins making the dough stronger and more elastic, giving the bread a better texture. Ageing can be achieved using chemicals or by leaving the flour exposed to air for a long time.

Making the dough

Other ingredients are added to the flour. These include water, yeast, extra fats, salt and bread improver.

Yeast is a type of fungi, like mushrooms. Yeast feeds on sugar and produces alcohol and carbon dioxide gas. This gas makes the bread rise.

Although there is a small amount of fat in flour, extra fat is often added to bread to make the loaves bigger and softer.

Bread improvers are added to speed up bread making. They can have a range of ingredients including food for yeast, chemicals to modify the proteins in the flour and emulsifiers to help the fat and water mix. One of the ingredients sometimes found in bread improvers is ammonium chloride. This decreases the acidity of urine and should be avoided by people with liver or kidney problems.

Salt is added to enhance natural flavours. There is usually 2g of salt for every 100g of flour.

All of these ingredients are kneaded into dough.

Baking the bread

As the bread heats up the yeast produces more gas. The heat also makes the trapped gas expand. Further heating kills the yeast and changes the structure of the proteins and carbohydrates so the bread dough becomes solid. Finally the surface browns as the bread dries out and the temperature increases even more. The browning is a result of reactions between sugars and amino acids—the building blocks of proteins.

White or brown bread?

For many centuries white bread was the food of the rich and famous. The extra step of refining the flour for white bread made it very expensive. This is no longer true with a higher price charged for brown, wholemeal and grain breads.

Wholemeal flour is made from all the constituents of the wheat. At least 90% of the flour in wholemeal breads is wholemeal flour while brown breads have at least 50%. Refining the flour removes not only the husk which gives the bread a brown colour, but some of the proteins, vitamins, minerals and fibre. However, the nutrients in wholemeal flour are not always as easy to digest and the extra fibre speeds their way out of the system.

So... we get more nutrients from white bread but brown bread is a better laxative. Which one you choose depends on what you are looking for!


Flowchart for making bread
magnifyFlowchart for making bread


Wheat field
magnifyWheat field


Agricultural spraying
magnifyAgricultural spraying


Flour milling
magnifyFlour milling


Mixing dough
magnifyMixing dough


Different kinds of bread
magnifyDifferent kinds of bread


Different kinds of bread
magnifyDifferent kinds of bread


White and brown bread
magnifyWhite and brown bread
© Museum Victoria Australia