Although dry packaged yeast can be purchased in the baking aisle of any supermarket, it can also be grown at home. In fact, using starter dough to grow yeast was how yeast was obtained prior to it becoming commercially available. Many bakers still prefer to grow their own bread yeast using the starter dough method. In this method, the original yeast colony is never completely diminished, and continuously repopulates when the yeast is fed.
In a glass bowl, combine 272 g (2 cups) of flour and one package of active dry yeast. Mix the ingredients thoroughly with a spoon to combine.
Pour 474 ml (2 cups) of warm water over the flour and yeast mixture. Mix thoroughly with the spoon until a dough forms.
Cover the bowl with a single layer of cling film and place it in a warm location.
Allow the bowl to sit undisturbed for 48 hours. After 48 hours, part of the yeast starter may be used for baking if desired. Place the remainder of the yeast starter in the refrigerator.
Feed the yeast once per week by combining 237 ml (1 cup of milk), 136 g (1 cup) of flour and 100 g (1/2 cup) of sugar. Pour the mixture into the yeast starter bowl and mix thoroughly.
Cover the bowl and allow the yeast starter to sit at room temperature for two to three hours after feeding. Place the bowl back into the refrigerator until ready to use.
Never use all of the yeast starter. There should always be at least 136 g (1 cup) of starter remaining in the refrigerator in order to continue growing the yeast colony.