These are the instructions we were given at George Brown College for making a sourdough starter. They are clear and detailed enough that following them carefully gives good results.
Day 1:
57 g Spring Water
70 g organic stone ground Rye Flour, preferably finely ground.
Activate the culture: Pour water into a very clean, clear, 2 L container (plastic works best). Stir until smooth. It will be thick. Scrape down sides and cover with plastic wrap. Let stand at room temperature (70F to 75F) in a draft-free area (like an oven) for 24 hours.
Day 2:
57 g Spring Water
70 g organic stone ground Rye Flour, preferably finely ground.
Feed the culture: Uncover and observe. The culture may have risen slightly. It will have a sweet, musty smell and taste mildly tangy. Pour the water into the container and stir with a clean rubber spatula until loosened up. Add the flour and stir vigorously to oxygenate the culture. It will be a little looser than the previous day, but still stiff, like oatmeal. Scrape down sides and cover with plastic wrap. Let stand at room temperature (70F to 75F) in a draft-free area (like an oven) for 24 hours.
Day 3:
57 g Spring Water
70 g organic stone ground Rye Flour, preferably finely ground.
Feed the culture: Today the culture will have risen up the sides of the container and may have already fallen. Th surface may be bubbly and if you hold up the container, you will see bubbles up the sides and on the bottom. It has an earthy acidic flavour and aroma. Pour the water into the container. You will notice strands of gluten floating in the water. Add the flour and stir vigorously to oxygenate the culture. Scrape down sides and cover with plastic wrap. Let stand at room temperature (70F to 75F) in a draft-free area (like an oven) for 24 hours.
Days 4 to 10:
Uncover the container and observe the culture. It should have become a darker grey-brown, and have expanded dramatically, maybe even doubling. It will be spongy looking and filled with small bubbles throughout. It should smell like a combination of over ripe apples and moist fall leaves. When you taste it, it should be acidic and sparkle on your tongue.
If it does not appear to be this active, just repeat the day 3 instructions every 24 hours for 6 more days. Use warm water (85F to 95F) and be sure to keep it in a warm draft free location. You may need to switch it to a larger container. After these additional feedings, if your culture does not look active, the flour may have been old, your water is too chlorinated, or your container may not have been clean enough. You may have to start again.
If your culture looks ready, repeat the recipe from day 3 but check back after only 12 hours. Scrape down the sides and cover with plastic wrap. Mark on the container, with a piece of masking tape, where the culture will be when it doubles. Let stand at room temperature for 12 more hours. You'll know it's healthy when it is almost doubled, and filled with large and small bubbles. It will smell and taste tangy.
Refresh the sourdough before using.
Refreshing the sourdough:
100 g Spring Water
75 g organic stone ground Rye Flour, preferably finely ground.
Once you have cultivated a healthy culture, you must feed it regularly to keep it that way. Refresh once a week, and keep it in the fridge when you're not baking. In the cold, the fermentation process slows down so that it does not need feeding as often. Be aware that the longer it ferments, the more sour your bread will be. Measure 1/4 cup (or 50 g) of your culture into a clean 1 L container and discard the rest. Stir in the water and rye flour vigorously until fairly smooth. Scrape down sides and cover with plastic wrap. If you plan to bake, mark on the container, with a piece of masking tape, where the culture will be when it doubles. Let stand at room temperature for 12 to 24 hours. If you don't plan to bake, let sit at room temperature for 1 hour, then refrigerate.
Maintaining the sourdough: If your sourdough has been in the fridge for a week without using, you will need to feed it. Weekly refreshment will keep it alive and healthy.
Preparing to bake: Whether or not you have refreshed it recently, you must refresh within 12 to 24 hours before using. Follow the instructions above. After it has fermented at room temperature for 12 to 24 hours, measure out what you need for the recipe. Place 1/4 cup of what is left over in a clean container, refresh and refrigeratue for up to 1 week.