In the jar combine the flour, apple and water. Mark the outside of the jar with a pen, so you can see what level the starer is at initially. Place the jar in a warm place, on a plate (in case there's an explosion!)

By the 3rd day you should have seen your starter bubble and fizz, the marker you've drawn should show you how much it has. Remove about 2 tablespoons from the starter, then add the flour and water. Mix to combine. Draw a new marker at the starters new place and put back in its warm spot.

Repeat the discard and feeding, like you did on day 2. The starter should smell fermented, but a bit sweet. If it smells of vinegar it's gone too far. You should discard most of the starter and add about 100g of flour and water to try to bring it back to a good level.

Over the next days repeat the discard and feeding. At this stage it can be brought out of it's warm spot, especially if it's too lively. There might be some liquid on the surface of the starter, this is called hooch and can be stirred back into it. Hooch means the starter is hungry and needs more flour!

After a week the starter should be strong enough to use in recipes. Keep the jar clean by scraping the inside of it down with a rubber spatula. It can be kept in the fridge, as this reduces the amount of feedings it needs (one every 3-4 days.)