Mother yeast, also called natural yeast, acid yeast, sourdough, natural leavening, natural leavening dough, mother dough, is a mixture of flour and water acidified by a combination of yeast and lactic acid bacteria that start fermentation of bakery or pastry dough.
Unlike the yeast that you buy in groceries that contains only Saccharomyces cerevisiae, the natural yeast includes many more species of yeasts and lactic bacteria.
When the water is mixed to the flour, the starch contained in it absorbs water, from that moment enzymes are activated and this will break down and transform the starch into glucose molecules which in turn will attract yeasts (living microorganisms that live around us, fond of glucose).
These yeasts, after a binge eating of glucose, will produce carbon dioxide, responsible for the rising process of the dough.
Once the dough is out of oxygen, yeasts will stop doing their job and lactic acid bacteria (that are able to work without oxygen) will start the fermentation process which produce lactic acid and other compounds.
Lactic acid task is sanitizing the environment, so the dough will have a lower ph and that increase acidity which will keep out pathogenic bacteria…. although not forever.
To keep mother yeast alive and ready for making bread or other products, it’s important to increase the colony of yeast by feeding him with glucose contained in flour. Doing this and controlling the environment temperature will help not increasing acidity in the dough that will cause the transformation of lactic acid in acetic acid, so a useless sourdough.
Refreshing mother yeast with new water and new flour is important to help it survive.
Mother yeast may vary from country to country because of the concentration and quality of yeasts in the air. So keep in mind that even if you follow a recipe step to step, you will get different results.
That explains why the taste of Pizza Napoletana cannot be replicated away from Naples City; however you may have good copies by following this authentic recipe.
Remember… “home-made strikes back!“.