How to Start a Sourdough Starter From Scratch
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A sourdough starter is nothing more than a living culture of wild yeast and lactic acid bacteria that you grow from flour and water. Those microbes are already present on the grain and in your kitchen, so you are not adding anything exotic. You are simply giving them a comfortable home and feeding them on a regular schedule until they become strong enough to leaven bread. The whole process usually takes between seven and fourteen days, and the only real skill involved is patience.
To begin, mix 50 grams of whole grain flour (rye or whole wheat both work well because they carry more wild microbes and minerals) with 50 grams of room-temperature water in a clean jar. Stir until no dry flour remains, scrape down the sides, and cover the jar loosely so gases can escape. Set it somewhere warm, ideally between 21 and 26 degrees Celsius. For the first day or two you may see very little, and that is completely normal. The early activity you eventually notice is often from bacteria you do not want long term, so do not get too excited by the first burst of bubbles.
Starting on day three or four, begin feeding once every 24 hours. Discard all but about 25 grams of the culture, then add 50 grams of fresh flour and 50 grams of water. This discard step feels wasteful, but it keeps the ratio of food to microbes high enough for the good yeast to thrive. As the days pass you can switch from whole grain flour to a mix of whole grain and white, or to all-purpose or bread flour, depending on what you plan to bake with.
Around day five to seven you should start to see real signs of life: a domed, bubbly surface, a pleasant tangy or yogurt-like smell, and a noticeable rise and fall between feedings. The clearest test of readiness is that your starter reliably doubles in volume within four to eight hours after a feeding. Many bakers mark the jar with a rubber band or dry-erase line right after feeding so they can track the rise at a glance.
If progress stalls, resist the urge to throw everything out. Slow development is almost always a temperature issue or simply a young culture that needs more time. Move the jar somewhere warmer, feed on a consistent schedule, and consider using a small percentage of rye flour to reintroduce vigor. Chlorinated tap water can occasionally slow things down, so if you suspect that, let your water sit out overnight or use filtered water.
Once your starter passes the float test, doubling reliably and smelling clean and sour, it is ready to bake with. From there you can keep it on the counter with daily feedings if you bake often, or move it to the fridge and feed it weekly if you bake occasionally. A healthy starter can last for years, even decades, with basic care, so the two weeks you invest now pay off for a very long time.