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The Science of Sourdough

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    Posted: 09 May 2010 at 04:45

Since there has been quite a bit of interest lately in sourdough, I'm going to post an excerpt from my favorite baking book "The Bread Baker's Apprentice" by Peter Reinhart, the undisputed king of breads.

Sourdough Bread and Variations
 
What we call sourdough bread should more correctly be called wild yeast bread, as it is natural wild yeast that leavens the loaf and not all wild yeast breads taste sour.More importantly, it is not even the wild yeast that makes the breads sour, but the acids produced by the various bacteria that inhabit the dough. These acids lower the PH level of the dough, creating a wake of flavors in the process, most notably the distinctive sourness we associate with sourdough bread. This is the microbial world, quite active beyond our sight, constantly changing the medium, the bread dough in which the organisms live.
 
There are dozens of valid methods of making wild yeast breads, and every bakery has it's own system. Some use a six-build system in which the starter is fed on a very specific schedule, at precise times with precise temperatures,building the dough into larger and larger volumes until the last "build" serves as the starter for the final dough. These various builds affect both flavor and structure. Some bakeries use a simple two-build system, using a large portion of the previous batch (25-35 percent) of the final dough as a starter for the next batch. Some systems use a wet sponge poolish-like starter, while other use a firm biga-like starter, or any combination thereof. Many systems use a combination of wild yeast and commercial yeast (called spiking the dough) to create a hybrid loaf that is flavorful, but faster rising and not too sour. Some bakeries use different systems for different breads (firm starter for one, sponge starter for one, spiked for another), while other bakeries use a single master system and apply it to all of their breads. In other words, no single rule governs how to make wild-yeast bread. I teach my students to first learn one system well, then feel free to learn as many systems as they want until they find the one that suits them best.
 
The wonderful village-style bakeries that now grace so many communities have introduced some beautiful and delicious variations of wild-yeast breads. They include multi-grain variations, breads made with flavorful supplementary ingredients, such as roasted garlic, onions, potatoes, rosemary and other herbs; and also wild-yeast rustic loaves made from wet dough. When we examine the art and science behind these loaves, we discover that each is made by the baker's chosen system and by his or her creative choice of ingredient variation. Again, each system involves choices: percentage of starter to use, method of starter, fermentation times and temperature, supplementary ingredients and design, and different blends of flours.
 
The following master system, like the one in my earlier book, Crust and Crumb, utilizes a three-build method. This sytem, however, uses a smaller percentage of wild-yeast starter and allows for greater variation in application. I still use both systems when I bake and teach. I love the chewy texture and flavor complexity of the Crust and Crumb sourdough ( after all, I won a national bread competition with it), but I also appreciate the flexibility of the new system.
 
I would be remiss if I did not say that if you already follow a system, whether self-taught or learned from another of so many excellent books available, you can apply the same principles to that system as you do to this one. That is...you can be creative. A particular system of builds will produce subtle flavor or texture distinctions that differ from those of another system, but both systems, assuming they follow sound bread-baking science, will produce wonderful bread. In most instances, my starter in someone else's system should work as well as theirs, and vice-versa. It is the thesis of this book that once armed with the empowerment tools of bread baking-knowledge and information-you should be able to navigate the infinite options available to you. The broad strokes of the following formula can be used to make an unlimited number of recipe variations. The finer strokes of these variations will be addressed at the end of the formula.
 
Bear in mind that this sytem is designed for home baking and takes into consideration that home bakers do not have a crew to whom they can pass on feeding schedules. Very few people, for instance, have climate-controlled proof boxes that produce consistent results day after day. We fly without such a safety net (and so do many professional artisan bakers, by choice), but we still have the power to maipulate time and temperature to create amazing bread. The use of refrigeration is a modern invention not available to the great bakers of previous centuries. They did their manipulations by scrulupous attention to feeding cycles. Cold fermentation gives us a wider berth and a greater margin of error, and allows us to call our shots regarding when to take the next step in the twelve-stage process of making bread. The following method will work with either organic or commercial flour and produces a mother starter, what I fondly call the Barm, in 5 to 6 days, depending on the weather.
 
Note: I have updated the original seed culture to account for a strain of leuconostoc bacteria that hinders many starters but generates lots of carbon dioxide in the early stage of a seed culture starter, making it seem that the wild yeast cells are growing rapidly. I learned from a group of dedicated home bakers (all contributors to the King Arthur Flour Baker's Circle) that the bacteria can be defeated by using pineapple juice on the first two days.
 
Seed Culture
Day 1
1 cup                                       (4.25 ounces)                       Dark rye or coarse whole rye
                                                                                            (pumpernickle grind) flour
½ cup                                      (4 ounces )                           unsweetened pineapple juice
                                                                                            room temperature
 
Day 2
½ cup                                      (2.25 ounces)                         unbleached high gluten, or bread flour
¼ cup                                      (2 ounces )                             unsweetened pineapple juice
                                                                                               room temperature
 
Day 3
1 cup                                        (4.5 ounces)                       unbleached high gluten or bread flour
½ cup                                       (4 ounces)                          water, room temperature
 
Day 4
1 cup                                         (4.5 ounces)                      unbleached high gluten or bread flour
½ cup                                       (4 ounces)                           water, room temperature
 
Day 1: mix the flour and juice together in a bowl until they form a ball of dough. Do not worry if the dough is soft or stiff, but be sure that all the flour is hydrated. Press this piece of dough into a 4 cup measuring beaker and place a piece of tape on the beaker to mark the top of the dough. Cover the beaker with plastic wrap and leave it at room temperature for 24 hours.
 
Day 2: The dough should not have risen much, if at all during this time. In a mixing bowl, mix the Day 2 ingredients with the Day 1 sponge, mixing with your hand or a spoon until all the ingredients are evenly distributed. The dough will be somewhat softer and wetter than the Day 1 sponge. Return this to the beaker, pressing it down , and replace the old tape with a new one to mark the spot. Cover with plastic wrap and ferment for 24 hours at room temperature. Do not be put off by the strong aroma of the dough; it will eventually brighten.
 
Day 3: Check to see if there has been a rise in the dough. There will probably be some fermentation but not a lot, perhaps a 50% rise. Regardless, discard half of the starter ( or give it to a friend to cultivate) and mix the remainder with the Day 3 ingredients. It will be a little wetter. Again, return it to the beaker and and press down to the same height as Day 2. Re-tape the beaker to mark the top and cover, ferment for 24 hours.
 
Day 4: The sponge should have at least doubled in size; more is even better. If it is sluggish and hasn't doubled in size, allow it to sit out for another 12 to 24 hours. Otherwise, discard half of the strarter and mix the remaining half with the new ingredients, returning to the beaker as before. Cover and ferment until it at least doubles in size. This may take from 4 to 24 hours. It is okay if it triples in size, but because it is now fairly soft and spongelike, it will not be able to sustain that large of a rise without falling. If it falls when you tap the beaker, that is the sign that your seed culture is ready to be turned into a Barm, or Mother Starter.
 
Barm
 
Makes approximately 6 cups ( 2 ½ pounds) barm
 
3 ½ cups                           (16 ounces)                       unbleached high gluten or bread flour
2 cups                               (16 ounces)                          water, room temperature   
1 cup                                  ( 7 ounces)                          seed culture
 
 Stir together the flour, water and seed clture in a mixing bowl ( you can discard the remaining seed culture or give it to a friend to build into his own Barm). Make sure the seed culture is evenly distributed and all the flour is hydrated. It will make a wet, sticky sponge similar to a poolish. Transfer this sponge to a clean plastic, glass, or ceramic storage container twice as large as the barm. When transferring the barm into the container, repeatedly dip your hand, spatula, or bowl scraper in water to prevent the barm from sticking to it. Cover the container with a lid or plastic wrap and ferment at room temperature for approximately 6 hours, or until the barm is bubbly. The plastic wrap will swell like a balloon, as will a plastic lid. When this happens, open the lid or release the plastic to let the gas escape. Try not to breathe it as it escapes-the carbonic gas mixed with the ethanol fumes will knock you across the room! Replace the cover and refrigerate overnight before using. The barm will be ready to use the next day and will remain potent for three days. After that, or if you use more than half during the next three days, you will need to refresh it as described next.
 
Refreshing the barm
 
The standard refreshment for a barm is at least double. However, you can also quadruple it, as the organisms in the barm are capable of feeding on a large refreshment and converting it into a starter. I double the barm at each feeding if I want a very sour bread, but I triple or quadruple it when I want a less sour flavor. Remeber, it takes longer fopr the bacteria to work than the yeast, so while a larger feeding dilutes both the bacterial and wild-yeast communities, the yeast bounces back faster than the bacteria, creating a strong, but less acidic leavening sponge. Eventually, the bacterial fermentation does catch up, by the second or third day, and the sponge becomes quite acidic and sour.
 
It is important to understand what happens when you refresh the barm. After 4 to 7 days, the acids and protease enzymes in a barm that has not been refreshed break down the gluten, turning what was at first a strong, stringy sponge into a protein-weak, potato-soup-like consistency.There are still plenty of live organisms to leaven bread, but they will make a flaccid dough. For this reason, it is advisable to feed your barm 3 days or less before you plan to use it. ( ideally, the day before). If you have a lot of barm but haven't fed it in a while, discard all but 1 cup and refresh it with 4 cups of lour and 2 ½ or 3 cups of water, stirring until all the flour is hydrated.
 
If you have been using and feeding your barm regularly, you do not necessarily have to discard any. However, what you do not want to do is, for example, use 1 cup of barm from your supply to make some bread, then refresh the remaining barm with only 1 cup of flour and some water. You must always at least double the4 reamining barm. You can do this by either throwing or giving some away before you refresh it, or using up more before refreshing it. (Remeber, you have a three day window before you need to feed it again)
 
If you do not plan to use the barm for a while, do not throw any away until you plan to refresh it again, and follow the guidance given above to refrigerate or freeze it in a tightly sealed container. Since you do not want to freeze a glass or ceramic container, you should transfer the barm to a zippered freezer bag that has been misted with spray oil (allow enough room for expansion and gas developement).
 
Use high-gluten flour for the refreshments (except in the case of a rye barm), as it has more gluten than in bread flour to withstand the acid and enzymatic degradation.
 
You can refresh in two ways. One is to weigh the amount of barm you plan to refresh and the other is to eyeball it. I use both methods and find that as long as you stay in the doubling to quadrupling ballpark, ty, you will have no problem keeping your mother starter strong, active and clean tasting. By clean tasting i meanthat no off-flavors develop, such as a musty or cheesy flavor caused by overfermenting at warm temperatures or by leaving it out too long. This allows unwelcome bactria to join the party or for the yeast to create too much alcohol, resulting in what we thing of as a yeasty flavor. The flavor is a combination of alcohol and glutathione, an unpleasant-tasting amino acid released by yeast as it dies.
 
The weighing method is simple: Weigh the barm and calculate how much flour and water it will take to double, triple, or quadruple  the weight ( the easiest way is to figure equal parts of water and flour). Thus, if you plan to refresh 1 pound of barm, you can build it to 2 pounds by adding 8 ounces each of flour (1 ¾ cups) and water (1 cup); or you can quadruple it by adding 1½ ponds of flour (5¼ cups) and 1½ pounds (3 cups) water.The larger the refreshmentthe longer the fermentation time, usually 4-6 hours, depending on the size of the refreshment and how cold the barm was when you started. If you are using a cold barm just out of the refrigerator, warm up the water to 90º to compensate and to hasten the onset of fermentation. Never let the starter actually be warm, however. It is best for the organisms we want to cultivate , the lactic and acetic producing bacteria , if the starter fermentas slowly, between 65º and 75º or at room temperatur.
 
When the starter is bubbly and foamy, put it in the refrigerator overnight before using it. Technically though, you could begin using it as soon as it foams up, but I wait for the overnight developement because I feel it gives the bread more complexity of flavor.
Either way, with a ripe and ready barm, you are ready to move on to the next build.
 
Basic Sourdough Bread
makes two 1½ pound loaves
 
Firm Starter
2/3 cup                                           (4 ounces)                     barm
1 cup                                              (4.5 ounces)                  unbleached high-gluten or bread flour
1/8 to 1/4 cup                                ( 1 to 2 ounces)             water
 
Final Dough
4½ cups                                        (20.25 ounces)               unbleached high-gluten flour or other
                                                                                            flour combination
2 teaspoons                                  (.5 ounces)                     salt
1½ to 1¾ cups                              (12 to 14 ounces)           water, 90º to 100ºF
 
1. Remove the barm from the refrigerator and measure it out 1 hour before making the firm starter to take off the chill. To do this, dip a 2/3 cup measuring cup into a bowl of water, thenscoop it into the barm to fill (the wet cup will allow the barm to slide out easily). Transfer it to a small bowl, cover with a towel or plastic wrap and allow it to warm up for 1 hour.
 
2. Add nthe flour to the bowl and mix together the barm and the flour, adding only enough additional water so that you can knead this into a small ball, about the texture of French bread dough. You do not need to work this very long, just until all the flour is hydrated and the barm is evenly distributed. Lightly oil a small bowl or mist the inside of a plastic bag with spray oil. Place the starter in the bag or bowl, turning it to coat with oil. Cover the bowl, or seal the bag.
 
3. Ferment at room temperature for approximately 4 hours, or until the starter has at least doubled in size. If it takes more time than 4 hours, give it additional time, checking every hour or so. Then, put it into the refrigerator overnight.
 
4. Remove the starter from the refrigerator 1 hour before making the dough. Cut it into about 10 small pieces with a pastry scraper or serrated knife. Mist with spray oil, cover with a towel or plastic and let sit for 1 hour to take off the chill.
 
5. To make the dough, stir together the flour and salt in a 4 quart mixing bowl (or in the bowl of your electric mixer). Add the starter pieces and enough water to bring everything together into a ball as you stir with a large metal spoon (or mix at low speed with a paddle attachment).
 
6. Sprinkle the counter with flour, transfer the dough to the counter, and knead by hand for 12 to 15 minutes (or mix with the dough hook for 4 minutes on medium-low speed, allow the dough to rest for 5 to 10 minutes, then mix for 4 more minutes). Adjust the water or flour as needed. The dough should be firm but tacky, like firm French bread dough. It should pass the windowpane test and register 77º to 81ºF. Lightly oil a large bowl and transfer the dough, rolluing it around to coat with oil. Cover the bowl with plastic wrap.
 
7. Ferment at room temperature for 3 to 4 hours, or until the dough has nearly doubled in size.
 
8. Gently remove the dough from the bowl and divide it into 2 equal pieces (about 22 ounces each), or divide it into smaller pieces if you are making rolls, being careful to degas the doughas little as possible. Gently shape the dough into boules, bâtards, or baguettes.
 
9. Proof the dough in bannetons or proofing bowls, on couches, or on parchment-lines sheet pans that have been dusted with semolina flour or cornmeal. Regardless of the method, mist the exposed part of the dough with spray oil and loosely cover the dough with a towel or plastic wrap, or slip the pans into a food-grade plastic bag. At this point you can either proof the loaves for 2-3 hours, or retard overnight in the refrigerator. If retarding, remove them from the refrigerator approximately 4 hours before you plan to bake them.
 
10. Prepare the oven for hearth baking as described on pages 91-94 making sure to have a steam pan in place. Preheat the oven to 500º F. Carefully remove the towel or plastic wrap from the dough 10 minutes before baking.
 
11. Generously dust a peel or back of a sheet pan with cornmeal and gently transfer the dough to the peel or pan, carefully removing the cloth from the top of the dough proofed in a bowl. If the dough was proofed on a sheet pan, bake it directly on that pan. Score the dough and slide it onto a baking stone, or just directly bake on sheet pan. Pour 1 cup of hot water into the steam pan and close the oven door. After 30 seconds, spray the walls of the oven with water and close the door. Repeat twice more at 30 second intervals. After the final spray, lower the oven temperature to 450ºF and bake for 10 minutes. Rotate the loaves 180 degrees for even bakling and continue to bake for another 10 to 20 minutes, or until loaves are done. They should register 205ºF internal, be a rich golden brown all over, and sound hollow when thumped on the bottom.
 
12. Transfer the loaves to a rack and cool for at least 45 minutes before slicing or serving.
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hoser Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2010 at 04:38

10. Prepare the oven for hearth baking as described on pages 91-94 making sure to have a steam pan in place. Preheat the oven to 500º F.

Here is a quick explaination of hearth baking, again from Peter Reinhart:
PREPARING THE OVEN FOR HEARTH BAKING AND LOADING THE DOUGH
     Many of the breads in this book are hearth breads, that is, bread baked directly on the hearth or a hot deck of the oven. The instructions will often read "prepare the oven for hearth baking". The pupose of hearth baking is to radiate heat directly into the bread as immediately as possible in order to promote oven spring and a crisp crust. Hearth baking may also employ steam to promote spring and contribute to a shiny finish to the crust. Most professional ovens have steam generators that create a mighty blast of steam with the push of a button. Most home ovens do not offer this feature, although some home ovens are now being built with a steaming mechanism.
 
     There are a number of ways to replicate a professional hearth oven in your home, although none quite match the professional oven's ability to retain heat and deliver a tremendous blast of steam. The first is the use of a baking stone, as discussed on page 39. You can slide your hearth breads directly onto a baking stone or unglazed quarry tiles using either the back of a sheet pan or a peel that has been dusted with semolina flour or corn meal.
 
     The second way to replicate a professional hearth oven is to use the double-steaming technique. Steam is not required for all breads but it is definitely important for hearth breads.
The steam delays the onset of gelatinization, allowing the bread additional time to spring in the oven. It also lends an attractive glaze or shine to the bread. It's value is only realized in the first half of the baking process. After that the bread needs a dry environment in which to develop its crisp crust. For this reason, all of the steam is generated during the first few seconds of the bake, with its effects dwindling as the bake continues.
 
     I used to advocate just spraying the oven walls with water to create steam, but then discovered a better way. While the oven is pre-heating put a heavy-duty sheet pan, or cast iron skillet either on the top shelf or oven floor. Before putting the bread in the oven, have hot water (simmering is best) standing by. As soon as you place the bread in the oven, pour the hot water into the steam pan and close the oven door. After 30 seconds, open the door and spray the oven walls with a plant mister...close the door, wait 30 seconds and repeat, then wait 30 seconds and repeat one more time.
 
    
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2010 at 05:04
Wow, I'm going to have to print this one out and put into my recipe book! Thanks for posting it  Thumbs Up
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hoser Quote  Post ReplyReply Direct Link To This Post Posted: 11 May 2010 at 07:55
OK...Tas has a starter going, and maybe someone else (not sure) so I thought I would start a seed culture with Peter Reinhart's method (above)

I'm using natural rye flour and pineapple juice for the first build of the culture. Hydrated all the flour.



Then press into a container.



Mark with a rubber band, cover and let it ferment for 24 hours.



After the second build, on Wednesday



Third build..Thursday. Cut the seed culture in half, discard half and mix with the day 3 build ingredients.





Press the mixed culture back into your container. I've been having trouble getting this to rise, so I decided to use a cold oven as a proof box. I just turned the oven light on which should generate just enough heat to help it ferment. I'll let you know for sure when I check it tomorrow, when it should be ready to be made into a Barm, or "mother starter."

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Meat Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2010 at 08:16
Great post. I'm still in the very early stages of bread making. Thanks to Bassman for a SD starter he sent me. I'm so glad I am able to be a member of this site. So much information to absorb, so many great ideas and recipes here. I only hope I live long enough to try them all LOL. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TasunkaWitko Quote  Post ReplyReply Direct Link To This Post Posted: 14 February 2018 at 12:10
A few weeks ago, I enquired with the folks at FarmSteady about how they might go about making a sourdough starter with their Kraut or Vegetable Fermenting Kit; in their reply they recommended this link, so I am adding it to the collective knowledge:

https://www.theperfectloaf.com/beginners-sourdough-bread/

I have not yet read it very thoroughly, so I can't comment on it; however, judging by a quick skimming over the material, it looks to be pretty involved, yet easy to read and follow.

If you are a visitor and like what you see, please click here and join the discussions in our community!
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