In short: A starter is raised from equal parts flour and warm water over 5–7 days: fed once a day at first, twice from the third day. It is ready when it reliably doubles or triples in 4–6 hours and smells sour and fruity, with no hint of acetone.
What you need
A spatula, scales, a tall clear jar and a rubber band to mark the level. Nothing else — the process is about patience and consistency, not equipment.
Which flour to start on
Wholegrain rye is the easiest starting point: it carries more wild microflora, so the culture comes to life faster. You can move it onto wheat flour later over three or four feeds.
Day by day
Day 1. Mix 50 g of room-temperature water with 50 g of wholegrain flour. Cover loosely and leave at 24–26 °C.
Day 2. Feed once with equal parts flour and water. You may see vigorous bubbling — this is not yet the culture you want.
Day 3. Activity often collapses. This is normal: one population of bacteria is giving way to another. Keep feeding on schedule.
Days 4–6. Move to two feeds a day. Activity returns, the rise becomes regular and the smell settles into something sour and fruity.
How to tell it is ready
A mature starter doubles or triples within 4–6 hours of feeding, holds a dome before it falls, and smells pleasantly acidic. Sharp acetone means it is hungry, not spoiled — feed it more often.
Frequently asked questions
Which flour is best for starting a starter
Wholegrain rye: it has more wild microflora and comes to life faster. Convert it to wheat later over three or four feeds.
Why did my starter stop rising on day three
That is expected. After the first burst of gas there is a lull while one bacterial population replaces another. Keep to the schedule and activity returns by day four or five.
What does a spoiled starter smell like
Sharp acetone, mould or something rotten. Pink or orange patches mean throw it out and start again; sour and fruity is normal.
Can a starter live in the fridge
Yes, but only once mature and not as a permanent home. Cold favours acetic bacteria and the starter turns harshly sour.