Add flour and water to a suitable lidded container and stir until well combined.
Pop the lid on and leave in a warm spot out of direct sunlight.
Day 2, you will find the mixture is thickened and begins to show some small bubbles and separation. Simply add 50g flour and 50g water and stir into mixture. Pop lid back on and pop it back in the warm spot.
Day 3 you may decide to remove a tablespoon or two from the mixture so you don't end up with too much. Once you gave done this put the discard aside and use it to make pancakes or in another recipe. Some people throw it away but I hate to waste!
Weigh the remaining sourdough starter. Whatever the weight you aim to double it by adding half the amount of water and half flour.
Keep using the same type of flour. Don't for example start with plain flour then switch to wholemeal.
Each day the starter will look a little unpleasant. It will begin to have a sour smell and when hungry will produce a watery yellowish substance called hooch. This can be carefully discarded before feeding with flour and water.
If you want to keep track of activity, since it's best used when active to make bread, pop a post it on container to mark the top of the mixture. You can then easily see if it has grown in size.
If you want to wait before the next feeding, for example if you run out of flour, just pop it in the fridge.
Keep maintaining it this way and it will last a very long time. Just use what you need in the recipe. If however you notice any black spots, this is mould and you need to throw it away and start over. This hasn't happened to me so far.
Some people like to name their pet yeast too lol.
