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Sourdough Bread

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Sourdough Bread

by Jack Lang (jackal10)


Dan Lepard, for inspiration and and contribution.

Charles Lang, whose hands are in the photographs.

Brendel Lang for the painting.

The Members of the eGCI team for considerable labour and expertise.

Samuel Lloyd Kinsey (slkinsey) my fellow instructor.

Jill Grey, my partner, for putting up with the mess.



The object of this lesson is to teach you to bake better bread— bread that will be the envy of your non-baking friends—bread so good that people will wonder where it came from!

The recipe is archived here.

Why sourdough? Because it tastes better. This is the real stuff; not some machine-made pap. You will make bread you just can’t stop eating, and that will spoil you for mass-produced bought bread. Once you have mastered basic white bread, you (or we) can go on to whatever variations you like or request. This is daily bread, fragrant with tastes of the yeast and the grain, and with a crisp crackling crust. Perfect on its own, or with good butter, or jam, or cheese and maybe a ripe tomato. It keeps (in a paper bag, not in the fridge) for close to a week, although you may need to toast it toward the end of the week. Toasted it makes magnificent bruschetta. You can bake weekly, or less often as the bread freezes well.

This recipe and technique may seem straightforward, but it contains the results of years of experimentation and optimisation. We’ll make plain, white bread. Once you have mastered that, you can go on to fancier loaves. However (unless you really need the bran) you will come back to this basic bread just because it is so good and so pure.

Bread comes in many shapes.


English bread shapes


European bread shapes

This lesson will teach the basic French boule or flattened ball shape. We will also look at baguettes. But you can make any shape you fancy. The same dough works well in a tin, too.

You can find more technical details regarding the history of sourdough bread and the composition of the starter by clicking this link. Reading this background history and science is not essential, but very helpful. It will give some insight into why as well as the how.

Where to get your starter

You basically have three options –

1. Buy a starter off the web or from a local artisanal bakery. One place is here.

2. Order the eGullet starter.

You can obtain the special egullet starter by sending a PM to jackal10 with your snail-mail address. The starter will be sent out free, although the cost of the starter and postage is about $10. Please donate at least that much to your favourite charity, and we would appreciate it if you could include the name of the charity and the amount in your PM.

Your egullet starter was collected originally in the vineyards of California, but has travelled extensively since. It produces a light, mild bread. When it arrives, it will look like raw dough in a plastic bag


How your starter will look when you unpack it.

You can leave it in the fridge until you are ready, or better, turn it into your own starter. To do this, add one cup of flour and 1 cup of water and mix to a smooth batter. You can do this by hand or in a food processor. Put the batter into a basin, cover and leave in a warm (80-85F/27-29C) place for 4-8 hours, or until you see bubbles on the surface. Ideally refresh it a couple of times, and you are ready. You can store the starter in a jar in the fridge.

3. Make your own.

You can make your own starter and harvest the local wild yeasts with some patience. The key is the remarkable stability of the yeast-lacto bacillus pairing. If you keep almost any fermentable mixture of flour and water at about the right temperature, and when it begins to bubble, feed (refresh) it regularly, you will get the right bugs.

Some people add grapes with bloom on them (yeasts live on the surface), rye (high in enzymes), or other things, but that is mostly superstition.

How to roll your own starter

a) Mix 1 cup flour and 1 cup water to a smooth batter.

b) Cover and leave in a warm (85F/29C) place until it starts to bubble (12 hours or so but it can take several days). Don’t worry about off smells or colours at this stage. Skim any obvious muck.

c) Refresh it by adding another ½ cup of flour and ½ cup of water and stir. If the volume gets too much for your container, throw some away. Cover the rest and put it back into a warm place.

d) Repeat the last step for 4 times at 8-12 hour intervals. The starter should be active, and smell wholesome.

Starters can be kept in a closed jar in the refrigerator for months. They may separate into two layers, but just stir them together before use. They will, of course, keep best if used and refreshed regularly. If the starter seems sluggish, refresh it a couple of times (step c above) before use.

Starter doesn’t freeze well, but can be dried for a reserve supply. If you need to ship it, make some into a lasagna sheet, or stiff dough.

For best results always use the same flour, so the bugs can get used to it. Some people keep separate starters for white, rye and for wholemeal (whole wheat). I use white unbleached flour, which has added Vitamin C as an improver. As mentioned above, if your flour does not already have Vitamin C in it, you can add 1/2tsp Vitamin C (Ascorbic acid) but it is not critical.

Recovering a sick starter

If your starter smells off (cheesy or of peardrops), or has gone sluggish you can recover it by following the procedure for a new starter above, but inoculate the initial flour and water mix with a tablespoon or two of the old starter.

Practical Section

A typical bread-making timetable is

Day 1:

09:00: Refresh starter

- Starter ferments -

13:00: Make dough

13:15: Dough kneaded (by hand)


13:45: Add Salt

14:00 Finished dough

- Bulk fermentation-

16:00: Shape

-Retard overnight –

Day 2

Pre-heat oven, and bake for 40 minutes.

Ingredients for 1 loaf or four baguettes.

To refresh the starter:

1 c sourdough starter

1 c Strong white bread flour

1 c water

For the dough:

1 c refreshed sourdough starter

3 c Strong white bread flour.

1 c water (you may need more -- see below)

2 tsp salt

The dough in the illustration is ordinary unbleached supermarket (Tesco) strong white bread flour, 11.7g protein, with ½ cup of spelt flour added for flavour. This supermarket adds Vitamin C and amalyse to their bread flour. Different flours may adsorb different amounts of water. This flour needs a bit more water. The object is to make a very soft dough -- one that has only just stopped being a batter and just holds together.

Sourdough Bread Instructions

A. Refresh the Starter

1. Mix together 1 cup starter, 1 cup strong flour and 1 cup of water. It should be the consistency of very thick cream.


Starter just mixed.

3. Cover, and allow to stand in a warm (85F/29C) place for 4 hours.


Starter after 4 hours.

After 4 hours or so, it should be bubbly. Temperature is fairly critical, as discussed above. Any hotter than 85F/29C and you start to kill the yeast; any colder and it will not be as sour and will take longer to rise.

What we are making here is a sponge starter or poolish. Starters (pre-ferments) can be roughly divided by hydration into wet, batter-like pre-ferments, often called poolish from their origin and dry, dough-like pre-ferments, often called biga, as the technique is typical of Italian bread. Some bakers call a poolish a sponge; others use sponge to refer to all pre-ferments.

B. Make the Dough

Assemble Ingredients as listed above.


The storage jar with the rest of the starter is at the back right, ready to go back into the fridge for next time.

The easiest way is to whizz together refreshed starter, flour and water (but not the salt yet) in a food processor for 20 sec.

Alternatively mix them in a large bowl:


Ready to mix


Dough after mixing.

Should make a softish dough. The wetter the dough the bigger the holes in the final bread. Different flours need different amounts of water – add more water or flour to get the right consistency. You may need to add up to another ½ cup of flour so that it just stops being a batter and holds together as a dough. On the other hand if it is too stiff then add more water. Plenty of loose flour will stop it sticking too much.

If you are making the dough by hand then knead for 10 minutes by the clock.


Be rough with it. Lose your temper with it. Take out your frustrations on it. Slam it about. When it is properly kneaded it should feel resilient to the touch. It has been described as feeling like an earlobe, but I describe it like feeling a soft breast or buttock. You should be able to take a pinch of dough and stretch it so thin you can see through it – called the “windowpane test”.


When kneaded the dough will stretch without breaking

You cannot over-knead by hand. It is possible (but quite difficult) to over-knead if you are using a mixer or a food processor, as the dough can get too hot, and if worked too long and hard the gluten will begin to break down.


Finished Dough

Gather it together, and wipe a little oil over the surface to stop it sticking, cover it and leave it in a warm place for 30 mins.



This pause, before the salt is added, is for several reasons:

- It lets the enzymes do their stuff. They begin breaking down starches into sugars to feed the yeast to make a better crust colour. Salt tends to retard this reaction.

- It lets the dough (and you) rest and relax after the exertions of kneading.

- It allows the flour to complete its hydration, High levels of salt can interfere with this.

- It allows time for you to prepare your “banneton” to receive the finished dough. See Preparing Your Banneton below.

After 30 mins add the salt and whiz for another 20 sec, or knead for another 10 mins. Oil, cover, and leave for 2 hours or so in a warm (85F/29C) place. The exact time is not critical – anything from about 90 minutes to 3 hours will work. Temperature is more critical than time.


Rested Dough

The dough will have expanded a bit. Don’t worry about whether it has doubled or not. A lot of nonsense is written in some cookbooks, resulting in much overproved dough. The dough will also have got a bit softer and wetter.

Turn out onto a floured board.


Dusting the board with flour

Now handle gently - don't knock all the air out. The time for rough handling is over. Take the sides and fold to the centre.


Folding the dough

Folding the dough like this (you can also fold top to bottom as well) gently stretches the gluten and the bubbles forming in the bread. Dan Lepard's technique for his wonderful bread is to repeat this folding operation every hour for up to 5 hours during an extended bulk fermentation phase, resting the dough between times. When the dough is ready for shaping bubbles are clearly visible if you cut a small slit

in the top of the dough with a sharp knife.

Turn the dough over and shape into a ball. As you shape it try and stretch the surface a bit so it is taut.


Shaping the dough

Put it upside down (on its stretched, taut surface) into a cloth lined basket (called a banneton). The top of the dough in the banneton will be the bottom of the finished loaf.

Preparing Your Banneton

Traditionally, bannetons are made of cane or wicker, lined with linen, but you can improvise from a basin or a basket and a tea-towel or a piece of muslin. Ideally they are porous, so the outside dries slightly to help in crust development.


Dough in the banneton

Don’t worry if the top surface of the dough in the banneton is uneven: it will even itself out. Put into the fridge, covered with a cloth, overnight.


In the fridge

The dough is soft and needs the support of the basket. You could bake it after letting it rise for a hour or so, but its easier to handle, and gives a better crust if you keep it in the fridge (retardation) for between 8 and 24 hours. The cold will practically stop the fermentation, and so timing is not critical, and it gives you back control in that you can bake the dough when you want, rather than when the fermentation dictates.

I’m lucky enough to have a brick bread oven that has a brick floor that holds the heat. The shell of this one I imported from France, from a company called Four Grandmere. If you are inspired to build your own, Dan Wing’s and Tom Jaine’s books are given in the references


My oven


Inside the oven

You can approximate a similar environment in a domestic oven by putting a pizza stone or a layer of quarry tiles or engineering bricks on the lowest shelf to provide bottom heat.

You are aiming for 440F/230C or even 500F/260C, as hot as most domestic ovens can manage. Heat the oven at least an hour before you want to bake to allow time to stabilise, and for the heat to soak into the tiles or equivalent. (If you have a wood fired oven you will need to light the fire about four hours before baking.)


My oven heating up

If you have an oven thermometer, check the temperature of the oven. You are strongly advised to do this as oven thermostats are surprisingly inaccurate.



When ready to bake, take the dough out of the fridge. Some advise letting the dough return to room temperature --a couple of hours or so, but I find I it better and easier to cook these very soft doughs straight from the fridge. The cold dough is stiffer, handles easier and spreads less.


The dough from the fridge

Again, don’t worry that it does not seem to have expanded much. Most of the expansion will be in the oven (called oven-spring). This will result in a lighter and better-shaped loaf than if the expansion is from proofing when some of the gas may leak out.


When ready to bake, turn the dough out onto a baking sheet and remove the cloth. (For the wood fired oven we use a peel, lightly dusted with dry polenta meal so the dough does not stick.)


Slash the top firmly with a very sharp knife. Professional bakers use a razor blade on a stick, called a “lame”. Slash quickly and decisively – it is a slash not a cut. Don’t mess the dough about. Spray the knife blade with cooking spray to prevent it from tearing the dough.


The slashes allow the dough to rise in a defined way, and lessen the resistance to expansion by making weak points in the crust. In ancient times the pattern of slashes identified whose bread it was in the communal oven.

Here a slightly careless slash has caught the dough on one side, so the finished loaf will be a bit uneven and rustic.


Into the oven:


Just loaded:


20 minutes later, and halfway through the bake. Most of the expansion has happened. Our loaf is the one on the left.


The pattern on the rye bread on the front right is created by using a banneton made from coiled cane. No cloth is used in that sort of banneton. Bannetons can be obtained from any good baking supplier. The ones shown come from Four Grandmere and the San Francisco Baking Institute.


Bake for 35-40 minutes, or until it is a good colour. You might need to rotate it after 30 mins.

Let the bread cool to warm before you slice it. Hard to resist the temptation to slice into the loaf too soon, but it needs time to finish cooking and for the structure to firm up as it cools.


I like an open texture, as it gives more room for the butter. The crust is a little thick as the bread was slightly over baked.


That completes the basic bread lesson.


Variations on the basic recipe/technique

I’d advise practicing plain white bread before trying variations. When you get that right you can get fancier. You might not get it completely to your satisfaction the first time, but as you go on your baking will improve. There are infinite variations possible.

Crust Variations:

My brother prefers a flour dusted crust. These were the other loaves in the bake:


To get this effect, lightly dust the banneton and the top of the dough with flour before putting in the dough.


The legs in the top of the picture are my sister-in-law, painting the scene. I’m the one sitting down; my brother is loading the oven.


The dough is slashed in a feather pattern. To achieve this, make alternate slashes from each side of the loaf to just over halfway across. This pattern was tought to us by Ian Duffy, then of the San Fransisco Baking Institute.


This is a loaf with 25% rye flour.

For a shiny, thinner crust, put an empty pan in the bottom of the oven and pour a cup of boiling water into it after you have put the bread in the oven (be careful of the hot steam), and shut the door quickly. The idea is to provide a burst of steam, which gelatinises the outside of the dough. Professional ovens have steam injection for this purpose. Alternatively (but not as good) you can paint the bread with water before it goes in the oven, or use a garden sprayer. (Be careful not to get cold water on the oven light or it might shatter.) The baguettes below are made like this.

Other crust variations you can try:

Brush with milk or cream

Brush with egg glaze (egg yolk+milk)

Toppings (stick on with egg-wash or water):

Porridge oats (oatmeal)


Poppy seeds

Sesame seeds

Grated cheese



Flavours and additions

Add with the salt, but you might want to chop them and then hand-knead them in – the food processor chops them a bit too fine

Onions (soften in butter first),

Hazelnuts, walnuts


Sun-dried tomatoes (oil-packed?)

Caraway seeds

Dill weed


Smarties or M&Ms

Seeds: Pumpkin, sunflower, sesame

Flour variants: I’d recommend replacing only 1/3-1/2 of the plain strong white flour with:

Wholemeal (whole wheat) (will not rise as much)

Granary (has added malt)

Rye flour (makes a sticky dough)

For dark rye add 1 Tbs black treacle (molasses). Some like caraway seeds as well.

Spelt (ancient wheat) (Poilane is reputed to use 1/5th Spelt. This was the example bread).

“Mighty White” (steamed, corned grains)

For a sweet bread: add sugar and butter with the fruit. Saffron for Easter.


Baguettes, that typical French loaf, are long thin loaves made with a soft, white dough. Because they are thin, they are baked at a higher temperature but for less time. The dough is delicate, and needs supporting continuously during proof and baking. You can get special pans for this. I’ve now thrown away my tin baguette pans (the ones in these pictures) and instead use a silpat baguette form (from www.demarle.com). You can just see it in the crust variation photo. Much easier and no sticking.

To Make Baguettes from the Finished Dough

Divide the dough into four, at the shaping stage:


Roll and stretch into long cylinders, tucking the end in neatly. Cover, put into a large plastic bag, like a dustbin liner so that they do not dry out too much, and put in the fridge overnight. Next day take them out, and slash the tops.


Put them in the hottest oven you can, and throw half a cup water into a pan or onto the oven floor. Beware of the hot steam!


Bake until golden, say 30 mins


Let cool on a rack. Enjoy with cheese and a glass of wine, or maybe some good soup.



Dan Lepard Baking with Passion - Dan Lepard - A great book. Website: www.danlepard.com.

Joe Ortiz The Village Baker ISBN 0-89815-489-8 wonderfully evocative.

Bread Builders. Hearth loaves and Masonry Ovens - Daniel Wing and Alan Scott. The definitive book on building and using brick bread ovens.

The Bread Baker's Apprentice - Peter Reinhart

Breads from the La Brea Bakery - Nancy Silverton

Elizabeth David English Bread and Yeast Cookery ISBN 0-14-046791 is, like all her books, masterly for its time.

Tom Jaine, Building a Wood Fired Oven for Bread and Pizza. Prospect Books ISBN 0907325

Web resources


www.fourgrandmere.com (Click on the Union Jack to get the English version).






www.faqs.org SLKinsey is a contributor- a good resource.

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Brief diversion on the history and microbiology of sourdough

Since antiquity, people have sought to leaven a simple mixture of flour and water by leaving it to ferment over many days. As this mixture fermented, yeasts (either introduced or present on the surface of the utensils and ingredients) would multiply and release carbon dioxide, aerating the final dough, producing a crumb that was soft and pleasant to eat. The remains of loaves leavened with these ferments have been found in the Pharaoh's tombs in the pyramids in Egypt. Similar breads are still crafted in the region.

Yeasts and bacteria are essential to our life on earth. They have helped shape what we eat and the way we eat for as long as man has cooked food. We have used these organisms to change the taste and texture of the foods we eat, and to preserve our foods through the leaner winter months. In baking, they are essential to many of the breads we cherish. For all of us, our ethnic baking practices are part of our cultural heritage, and replicating the traditional methods used to create them helps us maintain those links with our past.

One of the most famous breads, and the loaf that is held as the symbol of artisanal baking excellence, is the San Francisco Sourdough. The sourdough culture used to leaven this bread, and to give it its unique texture, aroma and flavour, is extremely stable. The method used to initiate and maintain the sourdough culture of yeasts and bacteria used in San Francisco Sourdough is typical of early, traditional baking methods. The bread made today is very similar to those ancient breads. Its stability made it the yeast of preference to take into new and remote places. Miners took it along on the Yukon Goldrush and early homesteaders of the US carried on their long treks to new territory. If we provide the right environment, this culture will grow and thrive, and make our bread rise.

Sourdough culture is a yeast living symbiotically with a friendly lacto-bacteria. We need to start with enough of the right organisms so that they can become the dominant culture, food and water and the right temperature.

Given the right organisms, the optimum temperature is just over 80F/27C. Much hotter and the activity of the yeast declines. Above 95F/35C the yeast is effectively dormant or dead. The bacterial activity peaks at 93F/34C, so some bakers choose to ferment at 90F/32C to get a sourer bread. At 70F/21C the activity of the yeast has roughly halved, so the fermentation will take twice as long.

You can chose to ferment at cooler temperatures - you may not have reliably warm place available - but if you do so you will need to compensate by increasing all the times in the recipe correspondingly. Temperature control is critical (within a few degrees) for optimum results. A thermometer is a baker’s best friend.

Our task is to create an environment that promotes optimal growth, but then starts to slow just before we put the bread into the oven. This is why the starter culture is built up in stages, (starter, then dough) roughly tripling in volume each time. (Some recipes for bulk production call for more stages: Starter, Clef, first leaven, second leaven, bulk fermentation, proof.)

Why not dump all the flour and water in at once? We want to ensure that our culture is the dominant species! Our kitchens, our flour and our water are not completely sterile. They, too, may harbour spores and if our culture is too diluted, some of these less desirable cultures could get a foothold. Roughly tripling the volume each time (1 of starter, 1 of water, 1 of flour) ensures that our starter is dominant. Varying the hydration and temperature of each stage gives some control over flavour as well.

A sourdough culture consists of a whole lot of little critters. There are maybe a several hundred different strains of yeast and friendly bacteria in there, some from the starter, and some carried in on the air and via the environment, or from the water or flour. In studies by Sugihara and colleagues on San Fransisco sourdough cultures, the dominant yeast was found to be a version of bakers yeast called Candida milleri species. They christened the dominant lacto bacteria (called a lacto bacteria not because it lives on milk, but because it secretes lactic acid, which is also found in milk) Lactobacillus sanfrancisco species. These two have learned to live well together, and like the best marriages they form a symbiotic relationship, supporting each other and keeping strangers out. The yeast has evolved to live in a highly acid environment, and breaks the starch in the flour down into sugars. The LB keeps the environment acid, breaks down some of the more complex sugars, such as maltose into simpler sugars that the yeast can feed on, and secretes a sort of anti-biotic to kill competitive bugs. You can read more in the Web resources referenced in the lesson.

The stability of the starter means that, providing we provide about the right environment, the culture will grow and thrive, and make our bread rise. Sourdough culture is a yeast living symbiotically with a friendly lacto-bacteria .We need

- To start with enough of the right organisms so that they can become the dominant culture.

- Food and water. Normal dough provides more than enough.

- The right temperature.

The right temperature is the single most critical variable. Michael Ganzle and his co-workers did some studies on this. They found the following growth rates of L. sanfranciscensis and C.milleri as function of temperature. Growth rate is ln2/generation time, i.e. a growth rate of 0.7 is a generation (doubling time) of about 1 h.

The generation times measured in laboratory media are different from that in rye / wheat / white wheat dough. If the generation time at 20 C is 1/2 of that at 30 C in my medium, the organism will also grow 1/2 as fast at 20 C compared to 30 C in dough (we checked). So, it's not the absolute numbers that matter, but the ratio of growth rate to growth rate at optimum temperature.

here is a table illustrating growth rates at varying temperatures.


When the environment changes, the culture does not react immediately but after a lag. Spicher defines the phases of growth as

1. Lag Phase: The organisms need to adjust to the new environment before growth can resume. This depends on the vitality of the inoculation. The time can be significant with dried cultures, which need to re-hydrate. In this phase, the greatest danger exists that a spontaneous flora from the organisms present in the flour will be able to alter the existing flora.

2. Acceleration Phase: The organisms are now adjusted to the new environment and start to multiply. The end of this phase is reached when the highest multiplication rate is reached.

3. Exponential growth Phase: The organisms are at their optimum growth rate, repeatedly doubling their numbers by binary fission.

4. Transition Phase: The growth rate decreases from the optimal rate. Possible reasons are exhaustion of nutrients, waste products accumulating acidity increase.

5. Stationary Phase: The number or newly generated and dying organisms is equal and it will not increase any further.

6. Death Phase: Initially, the number of dying organisms exceeds the number of newly generated. Later on, no new organisms are generated. Existing organisms die in increasing numbers for various reasons as mentioned in Phase 4.


Yeast food

The process of fermentation is the yeast feeding on simple sugars, like glucose and fructose, and turning them to into alcohol and acetic acid (vinegar). The sugars come from the starch being broken down by enzymes released by yeast cells. One enzyme is amylase (by convention, enzyme names end in –ase), which breaks down a component of starch, called amylose, into the sugar, maltose. This process is called amylisation. The yeast in sourdough can’t digest maltose, but our friend, the lactobacteria can, and they break it down into the simpler sugars, which the yeast can digest.

Commercial bread flours often contain small amounts of diastic malt, rich in enzymes, which helps break down the starch more quickly and make more sugar available to the yeast. Rye flour is sometimes used, but the rye enzymes, although more heat stable, are inhibited in the acid sourdough environment. Ascorbic acid, Vitamin C, is also used as a yeast growth promoter. If your flour does not already contain Vitamin C (read the small print on the bag) you could consider adding some. 1/2 tsp of Vitamin C powder (not the fuzzy kind) per bag should do it. Ordinary sugar, sucrose, promotes the growth of ordinary yeast in competition with the sourdough yeast. The sourdough yeast can’t utilise it directly, but the lactobacteria convert it to glucose and fructose, and then reduce the fructose to acetic acid (vinegar). The result is a sourer tasting (but not smelling) bread.

Ordinary baker’s yeast and sourdough don’t mix well. The sourdough environment is too acid for the ordinary yeast to thrive, and they compete for the available sugars. Some recipes use both yeast and sourdough, but this results in an ordinary yeasted bread, with the sourdough added for flavour, rather than for an acid ferment. A small amount of oil or a knob of butter can be added to the dough. Its effect is to make the strands of gluten slip over each other more easily and the finished bread is “shorter” with a softer crumb.

About flour and gluten

Gluten is the protein that holds dough together. If you take a piece of raw dough and wash it repeatedly under the tap, or keep chewing it, you will end up with a rubbery substance. This is the gluten. It acts like the rubber in a balloon. When the yeast ferments and produces gas, the gluten blows up into bubbles. It is these bubbles that determine the texture of the crumb in bread. There is some evidence that the bubbles form around the nuclei of tiny bubbles of air beaten into the mixture when it was originally mixed, so beat the dough well when first mixing.

If there is not enough gluten the bubbles leak or burst, and the bread does not rise well. Flour with a lot of gluten is called “strong”. Pastry flour is low gluten (weak), since the gluten would make the pastry tough and hard. Gluten content is not measured directly, but some idea can be gained from the amount of protein in the flour. Bread flour is typically around 12%.


The natural acid in the loaf is primarily made up of lactic and acetic acid (vinegar). Acetic acid tastes more acidic, but lactic acid smells sourer. How acidic the loaf tastes depends on many factors, including the ash content of the flour being used. But as a rough rule of thumb, if you want it sourer, ferment the starter for longer, or at a higher temperature.

Bakers percentages

Bakers express recipes (called formulas) in Baker’s percentages. In this formula, flour is always 100% with the other ingredients reckoned as a percentage of the flour by weight. Thus the starter, which is half flour and half water by volume, in our recipe consists of :

150g of flour = a baker’s percentage of 100, and 225g of water = a baker’s percentage of 150.

The main dough consists of:

Flour - 450g (100%)
Water - 225g (50%)
Starter - 200g (40%)
Salt - 9g (2tsp) (2%)
Total - 884 g

Roughly 15% of weight is lost in baking (mostly water) giving a final loaf weight of about 750g

Total flour (starter + main dough) 75g+450g=525g
Total water (starter + main dough) 112+225 = 337g or about 65% hydration

Hydration is a measure of how wet the dough is:

Stiff & Dry- 58 to 60% water Content
Firm & Tight - 60 to 62%
Modestly Firm - 62 to 63%
Malleable - 63 to 64%
Soft - 64 to 65%
Slack - 65 to 67%

American style breads usually are about 60 to 62% hydration, French style breads between 62 to 65%, and Italian style (ciabatta) breads upwards of a 68% range. Our dough is on the slack side because it has a relatively high percentage of water. But notice how little extra water is needed to change from firm dough to a soft one: 3% is 15cc or 3 teaspoonfuls for our amount of flour.


Sugihara/Kline/Miller, Microorganism of the San Francisco Sour Dough Bread Process, Applied Microbiology, Mar. 1971, 458

Gänzle et al., Modeling of growth of Lactobacillus sanfranciscensis and Candida milleri in response to process parameters of the sourdough fermentation, Applied and Environmental Microbiology, July 1998

Spicher, G., Handbuch Sauerteig, 5th edition 1999, Behrs Verlag, 61-64

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Temp C Temp F L.sf Yeast (C. milleri)
2 36 0.019 0.004
4 39 0.026 0.008
6 43 0.035 0.013
8 46 0.047 0.021
10 50 0.063 0.033
12 54 0.084 0.052
14 57 0.11 0.078
16 61 0.14 0.011
18 64 0.19 0.16
20 68 0.24 0.23
22 72 0.30 0.30
24 75 0.37 0.37
26 79 0.45 0.42
28 82 0.49 0.42
30 86 0.61 0.35
32 90 0.66 0.20
34 93 0.66 0.05
36 97 0.58 0.00
38 100 0.39
40 104 0.1
41 106 0.00

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