Keeping a leaven
You’ll get as many ways of keeping a leaven/starter as people you ask. My regime varies according to how often I bake. Currently, I’m baking on average around twice a week, so my leaven hasn’t needed regrigeration for a while.
The guidelines I work with are that a wheat leaven will need refrigeration if you aren’t planning on feeding/refreshing it with new flour/water for more than a few days. I’ve gone four or five without refrigeration, over winter: I’d guess if the weather was warmer then it would deteriorate more rapidly.
Mine is kept in a tupperware with a lid, and before baking is refreshed with a ratio of 1:2:2 starter:flour:water, so 50g starter would be mixed with 100g flour and 100g water (at room temperature). It is bubbling away nicely several hours later, or earlier if it’s warmer. This is called 100% hydration, i.e. the ratio of water to flour is 1:1. You sometimes see recipes which call for lower hydration, e.g. 70%, which would be a thicker mix as 100g flour would only be mixed with 70g water. Some suggest that a lower hydration keeps for longer. I keep mine hydrated to 100%, becaue it’s easier to work out, and have been successful with a nicely active leaven.
So, as a rule of thumb, to maintain an unrefrigerated active leaven, feed it at least every 3-4 days with twice as much flour and twice as much water as the bit you are refreshing. This can be upped to 1:3:3 and produce good results. Some people feed a leaven twice a day: morning and night, but mine is rarely refreshed more than once a day.
If you aren’t baking so frequently, then the wheat leaven can survive for a fair while, if it’s refrigerated. However, it may need an intermediate refreshment before use to perk it up. So if you started with 50g from the fridge, add 100g flour + 100g water (250g). If you left this for several hours it should be bubbling, and you could then take 100g from this and add 200g flour + 200g water to end up with 500g active starter.I have read that if you plan on keeping it for much longer then it can be frozen. I do have some in my freezer as an emergency backup, but haven’t so far gone that long without refreshing/baking to actually need it.
Uses for discarded/leftover leaven. I make bagels + sourdough muffins with mine, regularly, so rarely throw it away.
I keep two leavens, both wheat and rye. The rye one is more forgiving, and needs less frequent refreshes, which suits me as I tend to use less of it. You can mix and match leavens and flour in recipes: in my experience they are hardier than some would have us believe.