Unfortunately, the instructions involved making bread frequently in order to keep the starter alive. I don't eat much bread, so that wasn't going to work for me. I was sure that the culture would survive freezing, but I couldn't find any information on how to go about freezing and reviving it.
After some experimentation, I seem to have come up with a method that works reliably:
- Freeze your sourdough starter in 1/4 cup lots (I put 4 or 5 'blobs' of it on a silicone tray in the freezer, spaced well apart as my starter is quite runny). When they're frozen, store in a ziplock bag in the freezer. I don't know how long they keep like this, but definitely at least 6 months.
- A few days before you want to bake your bread, take one portion of starter out of the freezer and put in a bowl. Mix together 1/2 cup flour and 1/2 cup water and spread over the starter. Put it in a warm place (I use the hot water cupboard when the weather's cold) and cover loosely with a cloth. Don't cover it with a plate - the starter needs to 'breathe'.
- When the starter has thawed, stir it all together. Check from time to time. When it's risen and covered in bubbles (which will probably take 1-3 days) it's ready to either use or, if you need a large amount of starter, feed again. Further feedings should be at approximately 12-24 hour intervals.*
* To feed, stir it (so you can see how much you have); add about twice this volume of flour and about this volume of water (i.e. equal parts by weight); stir to mix; then leave it. It should produce enough gas to double in volume by its next feeding, so your container should be big enough to cope with this.
The bread recipe I use is as follows:
6 cups flour (1:1 wholemeal:white is nice)
1 T salt
3 T sugar
1/2 - 3/4 cup sourdough starter (revived from 1/4 cup frozen)
3 cups water
- (at noon) In a large bowl combine flour, salt and sugar. Add starter then water and stir until blended; dough will be very soft and sticky. Cover bowl with paper towels**. Let dough rest at least 12 hours, preferably about 18, at warm room temperature (e.g. in the hot water cupboard).
- (9.15 am) Check the dough. If it hasn't risen much (or at all) and is quite runny under a crust/skin, stir in extra flour till it's only sticky - this generally takes around 1 1/2 cups flour.
- Work the dough a little, folding it on itself till it doesn't get any smaller (should take less than a minute), then separate the dough into two balls. Generously coat a baking tray with flour, wheat bran or cornmeal; put each dough ball on the tray and dust the tops liberally with more flour, bran or cornmeal. Cover loosely with paper towels** and let rise somewhere warm for at least 2 and preferably 5-6 hours.
- (3 pm) At least 20 minutes before you bake the dough, heat oven to its hottest setting - around 250°C. Put two heavy oven-safe containers (cast iron, enamel, Pyrex, pottery or silicone; anywhere from 5-cup capacity up is fine) in oven as it heats, along with a shallow pan with a cup or so of water in it.
- When dough is ready (3.30 pm), carefully remove pots from oven. Drop the risen dough balls flour side down into the containers; it may look like a mess, but that is O.K. Don't worry if they've barely risen at all - they should still rise during baking and be fine. Shake pan once or twice if dough is unevenly distributed; it will straighten out as it bakes. Bake uncovered 30 minutes. Turn onto a rack and leave to cool.
With thanks to http://www.sourdoughhome.com for helping me to understand sourdough better so that I could develop a reliable method for making my bread :-)
** In general I'm not much of a fan of paper towels, preferring washable reusable cloths instead. However, after gumming up our washing machine with the tiny scraps of dough that had accumulated from many months of washing teatowels used this way, I came to realise that using compostable paper towels is much more sustainable than wrecking our washing machine!