I started a sour dough starter the first day of lock down, and so shocked to find that soon enough there wasn't enough flourin the shops to keep the starter going. Internet suggected drying the starter not freezing.
I now had a jam jar of dreid flakes of starter, and so with the last bits of whole meal, lots of porrage oats and about 200gms of plain flour reconsituted the flakes and created a loaf of bread.
I then got my order from Shipton Mill so I am happy - the starter from the flakes is happy, growing strong and making great loaves after its little experince! Dried starter can last for 100's and maybe thousands of years so this should be useful in a storecupboard!
Put a double sheet of grease proof paper on a baking tray
Cover paper in a thin layer of two table spoons of starter.
Dry in the airing cupboard over 24 - 48 hours.
When the starter is completly dry pull it off the paper in flakes.
You can leave as flakes or crush to a powder at this point.
Label and store in a clean jam jar with lid, at the back of your cupboard until you need it again.
Reconsitute in a little flour and water and build up over 48 hours before using as a starter.