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Slow bread: how to ferment your own bread

Before the arrival of commercial yeast a couple centuries ago, bread was made from a starter that was kept alive by bakers and in homes (see our video The way bread was made: fermenting with mother dough). Today, people are returning to the tradition in search of a tastier, more digestible, and perhaps healthier, loaf (see our video Slow bread from Barcelona Reykajavik).

You may not realize it, but you’ve probably tried a naturally leavened bread. Naturally leavens come with many names: sourdough starter in the U.S. (particularly in San Francisco), natural biga in Italy, natural barm in the UK, desem in Belgium and levain in France.

The way it was done

Yeast was first used to make bread in at least as far back as Ancient Egypt. It was probably an accidental discovery since flour and water left out longer than usual on a warm day will attract naturally-occurring airborne yeast and begin to ferment.

Since wild yeast lives on the plants, fruits and grains all around us, it is very simple to capture it for your own baking. Until just a few centuries ago, bakers and homemakers who wanted to bake bread did just that and then kept a natural leaven starter alive by continually feeding it more flour, often passing it down for centuries (San Francisco’s Boudin Bakery has used the same starter for their sourdough since 1849).

A renewed interest in naturally leavened breads has grown along with growing enthusiasm for fermented foods. There is recent research showing that the good bacteria, probiotics, that grow in fermented foods do have an effect on the body.

Additionally, many argue that during the time when breads like sourdoughs are given time to “proof” (rise), nutrients are released into the dough. Much has been written on the digestibility of naturally leavened breads. Author Meredith McCarty argues that sourdoughs are more digestible since their proteins are broken down into simpler amino acids and the complex carbohydrates into simpler sugars.

How to make a natural yeast starter

While you can buy a natural starter or inherit one, it’s very simple to make your own.


  • 1 cup* flour (white or whole wheat)
  • 1 cup water

* You can use more or less than 1 cup of each, just mix more or less equal parts water and flour.


  • A container big enough to allow the mixture to expand and foam up. A wide-mouthed glass jar or a small pottery bowl work well.
  • A cover: a natural fiber cloth (a cotton towel for example) works well. If you’re using a recycled glass jar, you can use the lid, with holes poked in it.


  1. Mix flour and water (at room temperature) in the bowl or jar.
  2. Lay a cloth on top (ideally, a dampened cloth).
  3. Leave at room temperature for 2-6 days. Any spot around 70-80°F is ideal, though as long as it doesn’t get hotter than 100°F, it will be fine.
  4. Some suggest stirring the mix daily, but others just let it sit.
  5. When ready, the dough will be moist, wrinkled, and crusty. It will be fully risen and won’t bounce back if you poke it.
  6. To be sure it’s ready, pull off a piece of dough and look for tiny bubbles and a sweet or mildly sour smell.

If you’re wondering why the mixture doesn’t start to mold or rot, it’s because the starch of bread flour isn’t digestible for most bacteria. On the other hand, wild yeast produce enzymes that can handle the starch so are attracted to the mix.

How to keep your starter alive

You can keep your starter in the refrigerator without doing anything to it for up to a month. Keep it in a container with a cover, but don’t seal the top as the yeast’s micro-organisms need oxygen to live. At least once a month, you will need to replenish your start.

To feed your starter, add a small piece of dough (from a batch of bread) or simply add more flour and water (equal parts of each). Stir the mix, but no need to stir much as the yeast will digest any lumps.

While you can keep your starter alive for decades, be sure to watch out for signs of things going wrong. If the water becomes really grey or sour, throw it away and start over.

Making bread from a starter

Once you have a starter growing, you can use it at anytime to make bread. There are lots of recipes for making bread from a starter, simply google “sourdough bread” or “bread from a starter”. Here is one recipe.


  • 6 cups flour
  • 1-2 cups water
  • 1 cup starter
  • 3/4 teaspoon sea salt
  • 2 tablespoons olive oil (optional)


  1. Mix starter with water and salt and then add to flour.
  2. Knead well until dough is smooth.
  3. Put dough in bowl and cover with damp cloth and leave it to rise in a warm place.
  4. Leave it to rise in a warm place: it should take 1 to 2 hours, or longer with some starters.
  5. Let the dough has doubled in size. If you poke it and it doesn’t bounce back, it’s done.
  6. Punch the dough down and knead a bit more.
  7. Make a loaf or two and place in a pan or on a baking sheet.
  8. Cover again and leave to rise again in warm place until it has again doubled in size.
  9. Place the pan in the oven set at 350 (do not preheat: this both saves energy and allows the bread to rise more slowly).
  10. Bake for 30-45 minutes.
  11. The loaf is done when it looks golden brown. It should also feel firm- no wet spots- and sound hollow if tapped on the bottom with a wooden spoon.