Mix ⅔ cups (85 grams) of flour in a non-reactive container (such as glass) with ⅓ cup (80ml) of warm water. Stir well.
Cover the container with a clean linen cloth, allowing it to 'breathe'. Do not use plastic or a tight fitting lid. Place the starter in a warm spot on your counter.
After 24 hours, feed the starter with another ⅔ cup of flour and ⅓ cup of water . Mix vigorously with a clean spoon, replace the cloth.
On Day 2 The sourdough starter should be fairly gloopy and may start to appear gluey. Make sure it is kept in a warm location to encourage growth! The warmer it is, the faster it grows!
At this point you should start seeing noticeable bubbles trying to break the surface of the sourdough starter.
Feed the starter again with ⅔ cups of flour and ⅓ cup of water. Scrape down the sides of the container, and replace the cloth.
On Day 4, your starter should have visible signs of yeast activity. This includes frothy bubbles, the starter growing in volume, and a yeasty smell.
Feed the starter one more time with ⅔ cups of flour and a splash of water to maintain the gloopy consistency.
Your starter should be easily doubling in size after feeding, and if it is, is ready to be used in baking!
Any leftover starter can be refrigerated, or continued to be fed to increase it's mass again.