Who doesn’t love a good chewy sourdough? I sure do. I’ve made sourdough bread off and on for years. Like many, I revived this practice during the pandemic. Heck I was home, why not? And I always liked creating a starter from the wild yeast and bacteria living in the forest around me. I thought I would look into the science of making sourdough and the benefits of if it.
What is sourdough bread?
Sourdough bread is leavened with natural bacteria and yeasts. Long fermenting times allows the bacteria and yeast to change the starches and sugars in the flour giving a savory sour flavor that varies with the different strains of bacteria and yeasts. This cocktail varies with different locations, for example, San Francisco is known for their local “flavor” of sourdough. Did you know that the mascot for the San Francisco 49ers is named “Sourdough Sam”? There is history there, actually.
What is the history of sourdough?
The oldest sample of sourdough bread was excavated from the area near Switzerland and dated to 3700 BC, but long fermentation is thought to originate in the Fertile Crescent with evidence of sourdough bread in Egypt pre-dating the sample from Europe. It is thought that brewing beer nearby managed to contaminate flour, leading to the used of fermented dough to make bread. Pliny the Elder wrote about sourdough. Sometimes grapes were used to “seed” the starter with natural yeasts, as were porridge, beer and wine. Legend has it that a crock of sourdough starter made it to the New World in the hold of one of Christopher Columbus’ ships.
In the mid-1800’s, sourdough bread was a staple item for our pioneers who kept starter in their prairie schooners, carefully nurturing them as they baked the breads that sustained them along their way. Sourdough became important during the gold rush period, as it was a portable source of leavening for the miners who were often on the move. In the Klondike, miners often kept fermented dough near there stoves, where the warmth kept the ferment going even in harsh temperatures. Some miners carried starter in a pouch around their neck, again, to keep the starter at a warm temperature.
How is sourdough starter made?
Making starter is easy: flour and water are blended and left uncovered in a mildly warm environment. I often start mine by placing it in a mason jar covered by a sieve out on my deck to collect environmental yeasts. Natural yeasts and bacteria in the flour are activated, where they grow. Whole wheat and rye flour have extra nutrients and starches that the bacteria and yeasts feed on. White flour is often used, but it is best to avoid flour that is bleached or brominated. These processes decrease the native microorganisms in the flour and make it more difficult to achieve the active processes in fermenting. Some recipes include the addition of sugar or even salt. Malt is sometimes added as it increases maltose, giving the bacteria a little more to metabolize. As mentioned earlier, sometimes other substances are added. Grapes or raisins contain natural yeasts. Pineapple juice supports the acidic pH of the lactobacillus bacteria that produce the sour taste.
Each day, a small portion of starter is removed, and an equal amount of fresh flour and water is added. This is referred to as “feeding” the starter. Recipes typically call for feeding once or twice daily. Longer or shorter intervals could be used; these will affect the strains that grow and the flavor of the product. Starter should be gloppy, not too thin (slower activity) or thick. You want to bake with starter at its bubbly, most active best. Whole wheat and rye flours ferment a little faster. Active starter will rise to double in size in 6-8 hours after feeding. High protein flour or adding less water can promote a better rise.
What is the science behind the rise?
In order to produce the leavening desired, sourdough bread must undergo a long fermentation time. When wheat flour is mixed with water, an enzyme called amylase increases. Amylase breaks down long starches, which are basically longs strings of sugars, into glucose and maltose. Yeast metabolizes these sugars, creating gasses that cause bubbles. Bacteria ferment resistant starches and break them down into more digestible starches. Yeasts metabolize maltose which in turn produces carbon dioxide, causing the dough to rise. For more detailed nerdy chemical explanations, look here Microorganisms | Free Full-Text | Sourdough Microbiome Comparison and Benefits | HTML (mdpi.com) and here Sourdough – Wikipedia.
The flavor of your bread comes from the intricate balance of different yeasts and bacteria, and the acetic and lactic acids they produce. The variety of bacteria and yeasts in a given starter will vary by many factors including the environment, the baker’s hands, how often starter is fed, which type of flour is used, and the amount of hydration.
What are some benefits from eating sourdough bread?
It turns out there are many advantages to eating sourdough bread, compared to commercially prepared bread. To begin with, the long fermentation (6-48 hours) of sourdough bread breaks down sugars in the bread. Thus, carbohydrates are less easily absorbed, so the glycemic index is lower. The glycemic index is a measurement of how quickly sugars are absorbed. This makes sourdough a good choice for people watching their carbohydrate intake. Lower GI foods keep you feeling full longer.
For patients with IBS, sourdough is lower in FODMAPS (indigestible starches) and may be better tolerated than commercial bread. Sourdough may cause less bloating, gas and pain in people that have trouble breaking down starches. This is due to the fermentation of resistant starches.
Enzymes created during the fermentation process break down phytic acid. Phytic acid is a natural preservative; it is why you can store intact grain for long periods of time. However, it also prevents absorption of vitamins and minerals. Decreased phytic acid means that you absorb more vitamins and minerals from sourdough bread.
Sourdough is filled with prebiotics. Prebiotcs are soluble fibers that provide an energy source to gut flora. I discussed it a few weeks ago here Your microbiome buddies – the benefits of taking probiotics – Health, Hope, Healing (healthhopehealing.net). How much and which prebiotics depends upon the flours used. In the c diff group I belong to there is a lot of talk about the role of sourdough in restoring a healthy microbiome. Prebiotics are a help.
What about probiotics? Baking does kill probiotics off. One site suggested there is data that shows some bacteria survive; I have not found it. Because yeasts are spore-forming I imagine that there may be yeast spores and possibly some bacterial spores depending upon the species in the starter. These could be of benefit to your microbiome.
OK, what do I do with my discard?
Oh, that’s easy! I don’t throw out starter discard (or anything potentially useful, come to that). There are numerous recipes for all kinds of things sourdough. Like, sourdough scones, crackers, cobbler, pancakes, waffles, rolls, pretzels, pita bread and just about anything you can imagine. Sourdough starter can also be dried for later use. While heat kills the yeasts and bacteria, starter can be gently dried, and even frozen.
Any good sourdough resources?
My favorite is King Arthur Flour. They have a whole learning center dedicated to sourdough, including lots of recipes for using your sourdough discard. I’ve included those links below.
Please join me for my for future posts, on topics ranging from antibiotic stewardship to how to talk to your health care provider, to hospice stories and some book reviews. I will need to take a bit of a break in a couple weeks so I will likely get off-schedule a bit, but plan to continue posting as close to weekly-biweekly as I can. See you next time!
Microorganisms | Free Full-Text | Sourdough Microbiome Comparison and Benefits | HTML (mdpi.com)
Sourdough Baking | King Arthur Baking
Sourdough Baking FAQ | King Arthur Baking