How does yeast make bread rise? Why do we need to knead most breads?

How does yeast make bread rise? Yeast is a small plant in the fungus family (that's ascomycetous fungi of the genus Saccharomyces, to you botanical nuts), and as inert as baker's yeast might seem to you in that little packet, it is a living organism.

Yeast manufacturers isolate one healthy, tiny cell, feed it nutrients and watch it multiply into tonnes of yeast.

One gram of fresh yeast contains about ten billion living yeast cells thus giving yeast the reputation as the rabbit of the plant world.

To serve the needs of bakers, manufacturers ferment the yeast to produce a more concentrated product.

But the yeast isn't satisfied to idly sit by in the fermentation containers – it wants to eat. So yeast is fed molasses and continues to grow.

Under ideal conditions, a culture bottle of yeast holding about 200 g will grow to about 150 tonnes in five days, enough to make about 10 million loaves of bread.

After it has grown to bulbous size, the yeast is separated from the molasses and water, and centrifuged, washed and either formed into cakes or dried into the granulated yeast that most consumers buy.

When the baker dissolves the yeast in water, it reactivates the fungus and reawakens the yeast's appetite as well.

Yeast loves to eat the sugar and flour in bread dough. As it combines with the sugar, fermentation takes place, converting the sugar into a combination of alcohol and carbon dioxide.

The alcohol burns off in the oven, but small bubbles of carbon dioxide form in the bread and are trapped inside the dough.

The carbon gluten, a natural protein fibre found in flour, to stretch and dioxide gas causes provide a structure for the rising dough without releasing the gas.

Why do we need to knead most breads?

When the dough doubles in size, the recommended amount, it is full of gas bubbles and therefore has a lighter consistency than breads baked without yeast.

By kneading the bread, the baker toughens the gluten protein structure in the dough, stretching the gluten sufficiently to withstand the pressure of the expanding carbon dioxide bubbles.