In a mixing bowl, combine 100g of all-purpose flour and 100g of water. Mix until there are no dry flour clumps.
Transfer this mixture to a clean jar or container, cover it loosely with a cloth or paper towel secured with a rubber band, and let it sit at room temperature (around 70°F or 21°C) for 24 hours.
On Day 2, discard half of the starter (approx. 100g), and add 100g of water and 100g of all-purpose flour. Mix well, cover loosely again, and let it sit for another 24 hours.
On Day 3, discard half of the mixture, leaving about 100g of the starter in the jar. Add 100g of water and 100g of all-purpose flour. Stir thoroughly, cover, and let sit for another 24 hours.
On Day 4, discard half (100g), then add 50g of whole wheat flour and 100g of water. Mix it well, cover loosely, and let it sit for 24 hours.
From Days 5 to 7, repeat the process of discarding half of your starter (approximately 100g) and feeding it with 100g of water and 100g of all-purpose flour daily.
After 7 days, your sourdough starter should be bubbly, have doubled in size, and have a pleasant, tangy smell. At this stage, it is ready to be used for baking.