Yeasts are all around us and have been used in the making of bread and beer as far back in time as the Egyptian civilisation – 4000 years ago. Classified in the kingdom of fungi there are currently 1500 identified.
The word yeast derives from the Old English “gist’ or “gyst” and the Indo-european root “yes” meaning to foam or bubble
For leavening sweet or savoury breads, the one most commonly used is Saccharomyces cerevisiae, which can be purchased in dried granular, easy blend or fresh forms. If purchasing fresh it should be a cream colour, firm and moist. Local bakers or health food shops should be able to supply you with bakers yeast.
These little single cell organisms simply do what they do naturally, benefitting both bakers and brewers (and us as consumers of course), by simply feeding on carbohydrates, it turns the fermentable sugars into carbon dioxide (CO2). The gas produced causes the bread dough to expand (rise) as the gas is trapped in pockets or bubbles.
Be aware though that salt inhibits yeast growth, which is why you keep them separate when mixing bread ingredients, and too much sugar will dehydrate the yeast, so easy does it. To help, follow tried and tested recipes.
Kneading bread dough helps develop the gluten in the flour, which in turn helps trap the carbon dioxide and enables the bread to rise and gives the bread flavour.