more sourdough starter instructions

i typed this up in an email to some friends i gave some starter to.

there’s 2 ways to feed sourdough – by weight and by volume, and there’s also a few possible situations – counter-top or fridge.
first rule is to always double it when you feed it.  this could be after you have used some or if you just need more for your recipe.
second rule is to always feed it every 12 hours if it’s on the counter.  i’m not sure how often in the fridge, but i’d say every 2 to 4 weeks.  you might find some clear liquid on the top if it’s been in the fridge for over 4 weeks – it’s alcohol (hooch?) that you can either dump off or stir back in.  you should be able to tell by smell if it’s gone bad.
third rule is to feed it equal amounts of flour and water by weight.  or by volume, 1/2 as much water as flour.
so on to the details.  when i keep mine on the counter, here’s what i do.  (i use a scale to weigh mine, but i’ll describe how using volume too.)
  1. weigh another identical jar, or otherwise know empty jar weight, so you know how much to subtract (the jar i use is about 280g or 10oz)
  2. weigh the jar with sourdough.  let’s say it’s 380g so there’s 100g of sourdough starter.
  3. if you’re just feeding it to maintain it, dump out half
  4. add back flour/water equal to the weight of the sourdough you have in the jar currently.  so if you dumped out half, you have 50g left.  you would need to add 50g of “food” back which would be 25g flour, 25g water.  if you didn’t dump out half, you have 100g of starter so you would add 100g more “food” – 50g flour and 50g water.
  5. stir it up
now if you don’t weigh it, you can use volume.  the jar probably has markings on it for cups or fl oz
  1. stir up the starter to remove all the bubbles otherwise you won’t get a good volume measurement
  2. read how much you have – say 1 cup
  3. if you’re feeding it to maintain it, dump out half
  4. add back “food” so the amount of flour is the same as the starter, and the water is half as much.  so if you dumped out half, you have 1/2c left.  you would need to add 1/2c flour and 1/4c water.  make sure the flour is very loose or you’ll have too much.  if you didn’t dump out half and you’re just doubling your starter to get more, you’d start with 1c of starter, and add 1c of flour and 1/2c of water.
  5. stir it up
another thing to know is the different stages:
  1. just fed – obviously this is just after you added flour/water and stirred it up.  it isn’t very usable at this point, but if you’re going to refridgerate it, this is the best time to put it in the fridge.
  2. active – this is a few hours after you feed it – it should get very bubbly and double in volume.  this is a good time to use it to bake something.
  3. mature – this is hours after it’s active, the bubbles won’t be strong enough to keep it inflated, and it will fall back down in volume.  it can still be used in some recipes but won’t rise much.  it will have small bubbles on the top and eventually will have a layer of clear liquid on the top (alcohol) but you can stir that back in before feeding it again.
to use it from the counter top, just feed it ahead of time and get the volume up to what the recipe calls for, then use it when it’s active.
to use it from the fridge – take it out, let it warm up to room temp, feed it probably two cycles to make sure it’s very active again before baking with it.  so if you want to use it out of the fridge, take it out the day before and feed it.
if you just used it and want to store it, just feed whatever is left according to the instructions above, then put it back in the fridge.

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