Sourdough starter feeding
A starter is flour and water that wild yeast and lactic acid bacteria move into. The yeast makes carbon dioxide to lift the dough. The bacteria make lactic and acetic acids, which give sourdough its tang.
The feeding ratio
A common feed is 1:1:1 by weight: starter, flour, water, such as 20 g of each. Discard most of the old starter first so the fresh flour isn't split among too many hungry microbes. A bigger feed, like 1:5:5, takes longer to peak.
Test yourself
Questions from the interactive lesson, with the answer and the why.
Where does the sour taste in sourdough come from?
Bacteria making lactic and acetic acids. The bacteria in the starter make these acids as they ferment flour.
True or false: Feeding a starter is mostly about adding water so it doesn't dry out.
False. Feeding adds fresh flour, which is the food for the yeast and bacteria.
Fill the blank: A fed starter is ready to bake with when its volume has roughly ___ and it is full of bubbles.
A fed starter is ready to bake with when its volume has roughly doubled and it is full of bubbles. A doubled, domed, bubbly starter has active yeast.
What went wrong? You keep topping up your starter with water only. It turns thin and sluggish and smells sharply sour.
Without fresh flour, the culture ran out of food. Yeast and bacteria eat the sugars released from flour, and water has none.
A starter sits in the fridge for two weeks. Why does it barely rise there?
Cold slows the microbes, so they eat and make gas slowly. The culture goes quiet in the cold, and a feeding wakes it up again.