Get Ready

1. Find a relatively warm place (68 degrees Fahrenheit to 70 F) to grow your starter. A colder environment stunts the growth of the sourdough yeasts.

2. Find a smaller, warmer place to keep your starter, if your home's normal temperature hovers below 68 F. Some good places include warm zones close to the water heater, atop the fridge and near a radiator.

3. Make sure your beer is truly flat, as carbonation will disrupt the process. This may require taking a small sip.

Combine Your Starter Ingredients

1. Mix your bottle of flat beer with an equal amount of flour, cup for cup. Whole-grain flour makes the best starter, as it contains more nutrients and microorganisms for the sourdough's active yeasts to feast upon. All-purpose flour, while it is not ideal, will still work.

2. Adjust your liquid balance. The goal is to introduce just enough liquid -- be it beer or non-chlorinated, filtered water -- to achieve a runny consistency like that of pancake batter.

3. Stir your starter thoroughly, ensuring that there is no dry flour in the mix.

4. Leave your starter in a nonreactive bowl: either glass, earthenware, stainless steel or food-grade plastic.

5. Cover lightly with a towel.

6. Leave the starter undisturbed for a full day. There may be no perceptible activity at all during this time period, though you may notice some growth and the formation of bubbles.

Maintain Your Starter

1. Remove half the starter after 24 hours and mix in about a cup of flour to "feed" the yeasts. You may choose to throw out the extra starter, but many bakers choose to give it to a friend -- or use it in a "discard starter" recipe, of which there are many.

2. Mix well, cover lightly and leave undisturbed in a warm spot for another 24 hours.

3. Check for activity on day 3. At this juncture, you should see bubbling, smell a fresh, sourdough aroma and notice a growth in volume. If this is true, ramp up to doing a "feeding" every 12 hours. Each time, use just 4 ounces of the starter, discarding the rest. Mix the starter with 1 cup of flour and either more flat beer or 4 ounces of non-chlorinated, filtered water.

4. Repeat twice-daily feedings until your starter becomes very active: delicious-smelling, bubbly and eager-to-grow. After about a week, it'll be ready to bake.

5. Keep a small amount of the original starter and repeat the process as long as you wish. Maintained fastidiously, sourdough starter can last for months -- years, even.