The cookbook I'm using tells me how to make a sourdough starter, but not how to feed it after I take out what I need for the bread. What do I do with the starter once I've used some? I don't think I'll use all of it at once.
I feed starter with a 50-50 mix of water and flour. Usually 1/2 cup water 1/2 cup flour for a small container. You can eyeball the ratio. It isn’t critical to get it perfect.
If you keep the starter in the fridge you can get away with feeding it twice a week depending on your yeast strain. You can do this by eye…if the starter starts to look ugly when you take it out to feed, you should feed it a little more often.
One thing I will say is that you can resurrect a starter that seems long past edible. The starter will get a cloudy fluid on top of the batter and develop a really strong smell if you let it go too long. My personal experience is that you can pour off the watery fluid and some of the batter if need be. Then add a good feeding of flour and water. It will take a little longer than usual to build up again. Yeast is a very durable critter.
When I've made and used starters in the past I've generally fed it 1/2 cup water and 1/2 cup flour every other day. The challenge with sourdough starters is that you need to be using them regularly as the volume obviously grows if you're just feeding it and not using it regularly. Of course a friend, family member, or neighbor might be thrilled for you to share it with them but then again...it's kind of like having a pet - you have to keep it fed!
You just have to add more flour and water periodically so your yeast doesn't die. You can add more to replace. You don't have to feed the starter as often if you leave your starter in the fridge but then you have to let it warm up before you use it.
This video is awesome for showing how to make and maintain your starter.
Maintaining a Starter:
As a general rule: Once your starter is healthy and active, bubbling, rising vigorously, and smelling sour, you have two options:
If you store the starter at room temperature, you need to feed it twice a day. Don't wait for the risen starter to collapse before the next feeding, because it messes with the ph levels and can make the yeast and bacteria less active. Every 12 hours, feed it.
If you store the starter in the fridge, you can go up to a week between feedings. The cold won't kill the yeast and bacteria, it just slows them down. Just make sure the starter doesn't get shoved into a super cold spot and freeze.
The feeding process:
Stir the starter, remove all but 4 ounces of it (you can either discard the rest or use it to bake something). To the remaining 4 ounces, add 4 ounces flour and 4 ounces of purified or bottled water (chlorine in tap water is bad for the yeast and bacteria, and most filters remove chlorine taste, but not all the chlorine). Room temperature starter gets room temperature water; refrigerated starter gets lukewarm water. Stir until no dry flour remains. Cover with a non-airtight lid. Refrigerated starters need to stay at room temperature for several hours after feeding so the yeast and bacteria have a chance to wake up and eat.
After removing some of your starter to bake bread, feed the remainder as you normally would, but perhaps with a bit more flour and water than usual if you're left with less than 4 ounces.
This can be avoided by planning ahead. The day before you want to bake, when you feed it, put the removed starter in a bowl and feed that, too. Your primary batch of starter won't be depleted, and you'll have plenty of starter for your baking.
I don't do sourdough in warm weather, it wastes too much flour. In the cooler months I use half the starter once a week and then add 1 cup flour and one cup water and watch the mix, when bubbles stop appearing (use a ceramic bowl with at clear glass top), will either make up another batch of bread or pour out half the starter and add the 1 cup of flour and one cup water. This refreshing of the starter is temperature related; the warmer it is the faster the yeasts work and the more often it must be renewed. I keep mine on the floor in a cool part of the kitchen. If you see pink in your starter, toss it and start over.