How to make a sourdough starter from scratch. This is a very simple process, just follow along exactly as it’s laid out in this video. Couple tips, always keep your starter warm NOT HOT. I keep mine on the counter at home around 70 degrees. Use Luke warm water the ja either from the sink or filtered. Any all purpose flour will work as long as it is unbleached and unbromated. Day 1: Mix 25 g water and 25 g flour together. Cover with paper towel and let sit for 24 hours. Day 2: To the same jar, ad