Step 1: In a clean glass jar or plastic container, combine the warm water, sugar, potato flakes, and active dry yeast.
Step 2: Stir thoroughly with a wooden or plastic spoon until the sugar is mostly dissolved and no dry clumps of potato flakes remain.
Step 3: Cover the container loosely with a lid or a piece of cheesecloth and let it sit at room temperature for 3 days to ferment.
Step 4: Stir the mixture once daily. You will notice it becoming cloudy and slightly bubbly by the third day.
Step 5: On the third day, the starter is ready to use or can be placed in the refrigerator for storage.
Step 6: Feed the starter every 3 to 5 days with 1 cup warm water, 3/4 cup sugar, and 3 tablespoons potato flakes to keep it active.