I’ve been making sourdough for several years. My sources — where you can find much more info — include Tartine Bread (by Chad Robertson), Cooked (by Michael Pollan), and How to Bake Everything (by Mark Bittman). What follows is my own mashup of these into a technique that works well for me.
Starter is the foundation of sourdough, its essential defining feature. It's become easier to get sourdough starter (I know of a few bakeries in Winnipeg that provide it for free or nearly free). But making it is pretty easy and lets you participate in the magic of collaborating with the wild yeast that's just freely cohabitating with us all.
My basic process:
Put about 1C flour in a smallish bowl (use a mix of flours that resemble the loaves you plan to make; I use 50/50 whole wheat and white bread flour).
Add enough warm water to make it into a thick batter, about the consistency of pancake batter or slightly thicker. Mix the water and flour together with your hands. Cover with a tea-towel or some other fabric and let sit. A warmer location will move things along faster than a cooler location, but normal house temperatures should all work eventually.
Every day, give the starter another mix with your fingers. If you find that it’s thickening, add some more water to keep it at a batter-like consistency.
Repeat. Have patience. After a couple of days, the starter will probably start to get watery looking and smell “off” or "cheesy." Continue! Various wild microorganisms are colonizing the batter. (You are stirring with your hands and covering it with a porous cloth to encourage this.) The first ones to mature are unhelpful and unpleasant. Wild yeasts should eventually take over and displace them. Nature is amazing!
After a few more days of stirring and waiting, the starter should begin smelling decidedly yeasty / bready and starting to develop bubbles. At this point, I pour half of the starter down the drain and make it up again with enough flour and water to maintain a thick battery consistency. If the yeasts are taking hold, then the next day it should be decidedly yeasty smelling and very bubbly. You have starter!
- Sometimes the yeast doesn’t take hold, and the starter just spoils. That’s wild sourdough for you! I just start again and hope for better luck. Making wild starter is famously fickle, so expect to have to try more than once.
- Some folks swear by adding a small piece of fruit to the batter (pineapple gets recommended a lot). I haven’t had to do that.
- I've also seen advice to leave the starter alone/stop messing with it once it starts to show signs of fermenting/transformation.
- If you're 4-5 days in and not much is happening or things smell "off" rather than "yeasty", try getting rid of half of the starter and topping it up with fresh flour and water.
- You'll probably have better luck with organic/stone ground flour than commercial flours, but I've made starter with Rogers flour no problem. Rumour has it that rye also works better than wheat, but I've only used wheat.
- You can also cheat at any point by adding a tiny pinch of commercial bread yeast. You won’t have a purely wild starter to work from, but you’ll have a starter!
Keep the starter in the fridge. If you bake weekly, that's all the maintenance it needs.
If you don't get around to baking, you need to feed the starter every week or so: dump 2/3 - 3/4 of it down the drain. Add enough flour and water to make it into a very thick batter-like consistency. (I use a mix of white and whole wheat to feed.) Stir and return to fridge. You can experiment with volumes of water and flour; you want enough starter so you can put most of it into a loaf, giving the loaf the right amount of moisture, but leaving enough starter left to build a new batch. (You can get a starter going again from very little; microorganisms are amazing.) I usually have about 2C of starter.
If you keep the starter in the fridge and either bake or feed it weekly, it will last indefinitely.
(And for full disclosure I should probably clarify that I've baked hundreds of loaves of sourdough but only made starters a few times. Fortunately it only has to work once and you can keep that sucker going for years.)