A Close Look at the Bacteria and Yeast in the Sourdough Starter

Vanessa Kimbell wrote . . . . . . . . .

I spent last week with Karl from The Sourdough Library, who has taken a sample of my sourdough starter back the library in Belgium, where there is collection of 91.. ( yes we are number 91) and he has sent the other sample to Marco Gobbetti, who I met in September, from the university of Bari, to be analysed.

It will be 45 days before the full yeast and lactic acid bacteria identification and analysis is complete, hopefully in time for the results to go in my book. In the meantime, this piece I wrote three years ago, will perhaps give you some indication of how fascinated I have been and perhaps give an indication of just how excited I am to have the lactic acid bacteria and yeast strains identified.

When I am teaching sourdough bread making on the course here, I often refer to my starter as a sourdough cultures. It’s a good name that reflects a little of what is going on, as sourdough is a complex ecosystem containing multiple species of yeast and lactic acid producing bacteria. Despite having had a close and somewhat intimate working relationship with my starter for more years than I can remember I had never actually see my starter close up I was recently lucky enough to be invited to Lalemand, the UK’s largest yeast manufacturing factory in the UK and I was thrilled when they offered to take a look at my starter and analyze it in the laboratory. Seeing my starter under the microscope was almost as exciting as opening my stocking on Christmas day. The technician dropped some of my starter into a solution and placed it under the microscope – and there they were – my yeasts and my bacteria. Wild sourdough yeasts don’t live alone in a monoculture. Unlike baker’s yeast, dormant cells of bacteria float through the air all around us and hang about in wheat waiting for a place to call home. When they find wheat they begin to reproduce and their digestive process is “fermentation.” To see these microorganisms close up with my own eyes and seeing both the yeast and bacteria side by side was magical.

The yeast and the bacteria have a mutually beneficial symbiotic partnership sharing all the available nutrients form the flour. Rather than compete for food they cooperatively protect their ecosystem from other uninvited bacteria. The yeasts are tiny oval shaped one-celled fungi and when they have access to oxygen aerobic fermentation produces carbon dioxide gas (CO2.) These are the bubbles that you see in the bread dough which is what makes your bread rise. I’d just fed the starter the night before on the basis that I wanted it to be as lively as possible. So I was even more fascinated to see them move. The yeast’s made their way around the petri dish like footballers running around a pitch in a random manner.

When they are aerobic then they are at their most active. Of course, when the yeast ferments in the absence of oxygen (anaerobic fermentation) it produces alcohol and slows down, which is why when you see a sourdough culture that has been left to ferment for a while without being aerated or fed develops a thin layer of alcohol (called hooch) on the surface. It is this alcohol combined with lactic acid that provides an additional flavor dimension. I’ve been baking with sourdough since I was a little girl and I never tire of it. The idea that there is an ecosystem in a pot that behaves differently according to the conditions that it lives in fascinates me. The Sourdough bacteria are much tinier than the yeast and are lactic acid-producing bacteria (lactobacilli) (these can also be found in numerous other fermented foods and it is these bacteria that produce the unique flavors and textures. They are also responsible for the increase the nutritional value of sourdough bread, through digesting the indigestible bits of flour.

The bacteria eat carbohydrates, fats and proteins and then produce acids, most notably lactic acid and to a lesser extent acetic acid (vinegar). The pH of sourdough changes according to the stage of fermentation it is at but in general it has a pH 3.5 – 5. It is this acidity that keeps out of pathogenic microorganisms such as botulism bacteria, E. coli bacteria and spoilage fungi as it is unable reproduce in an environment with a pH below 4.6. Nevertheless I was shocked as the technician took a swab and labeled up the peti dish as E-coli. I had never considered that my sourdough might have bad bacteria in it. “You’ll have to wait three or four days until we know if it has any E-coli or other nasty’s in it.” he said with a grin.

I have to admit I really wasn’t expecting this aspect to be tested, but was greatly relived to have the results back which gave my starter the all clear. I was confident that the Lactic acid bacteria had protected the ecosystem and prevented pathogenic microbes from invading the sourdough ecosystem and upsetting the balance. It is these same organic acids that keep sourdough bread mold-free far longer than bread made with baker’s yeast.. All in all it was fascinating to see my sourdough ecosystems is healthy and resilient, especially as this one is an heirloom sourdough starter that has been passed down for many generations.

Source: The Sourdough School


Whole Wheat Sourdough Pancakes


9 ounces (about 1 cup) “ripe” whole wheat starter
5 ounces (1 cup) whole wheat flour
1/2 cup milk
2 tablespoons butter, melted and cooled slightly, plus a little for the pan
2 large eggs
3 tablespoons maple syrup
1 teaspoon vanilla
1 teaspoon fine sea salt
1 teaspoon baking soda


  1. In a large bowl, mix together the starter, flour and milk along with one-half cup water until smooth. Let stand 30 minutes while you melt the butter and prepare the other ingredients.
  2. Whisk the melted butter, eggs, maple syrup, vanilla, salt and baking soda together until smooth, then stir the mixture into the bowl with the starter. Blend only until combined.
  3. Heat a skillet or cast-iron pan over medium heat and add a nub of butter. Pour in about one-fourth cup of batter, and cook until bubbles form on the surface of the pancake, 1 to 1-1/2 minutes. Flip and cook until the bottom of the pancake is slightly browned, 30 seconds to 1 minute. Repeat, adding more butter to the pan if necessary. Serve immediately.

Makes 14 to 15 pancakes.

Source: Los Angeles Times

Sourdough Starter Made with Milk and Yogurt

A sourdough starter is a portion of dough that is allowed to ferment. When this happens, the wild yeast and bacteria in the flour, in the liquid, and even in the air break down natural sugars and produce carbon dioxide, which enables bread baked with the starter to rise. As it ferments, the starter also produces acidity—in the form of lactic acid and some acetic acid—creating the “sour” in sourdough.

Starters vary from place to place (because wild yeasts are different everywhere) and baker to baker. The ones that developed in the San Francisco area were uniquely sour. In fact, the bacterial strain that’s responsible for that sour flavor was eventually identified and named Lactobacillus sanfranciscensis in honor of San Francisco.

Once established, a starter can be kept going for decades. Boudin Bakery, founded in San Francisco in 1849 and still operating, traces its sourdough starter to one begun more than 150 years ago by Isidore Boudin. (The Boudin starter was borrowed, so the story goes, from one of the actual “sourdoughs”—the name given to gold miners because they relied so heavily on sourdough starters for bread baking out in the gold fields.)

Sourdough has been a standby at Sunset since 1933, when we published the first recipes. However, we discovered that capturing the right bacteria and yeasts to establish a good starter can be hit or miss—some mixtures never fermented at all, while others were weak or inconsistent. In 1973, staff food writer Kandace Reeves, working with microbiologist Dr. George K. York from the University of California, Davis, finally hit upon a truly dependable starter using yogurt.

Sunset’s reliable sourdough starter

As with a classic starter, ours ferments flour and liquid—milk, in this case—with some yogurt, already packed with helpful bacteria to get things off to a good beginning. Yogurt also produces a very active, bubbly starter and gives a wonderful zesty flavor to the bread. After a few days’ incubation in a warm place, the bacteria multiply to break down sugars in the flour and milk and give the characteristic sour smell and tang, and the starter is ready to use.

Despite its terrific souring qualities, yogurt-based starters don’t always have a reliable yeast component (their high levels of acidity can inhibit yeast’s gas production), so we add dry yeast when baking. For best results, use milk (nonfat or low-fat for tangiest flavor) and yogurt that are as fresh as possible (check the sell-by date) and use them right after opening.


Makes: About 1-1/3 cups starter in about 1 week


1 cup nonfat or low-fat milk
3 tbsp plain yogurt (any fat level; use a brand with live cultures and no gelatin)
1 cup all-purpose or bread flour


  1. In a 1-qt pan over medium heat, heat milk to 90° to 100°. Remove from heat and stir in yogurt. Pour into a warm 3- to 6-cup container with a tight lid.
  2. Cover and let stand in a warm (80° to 90°) place until mixture is consistency of yogurt, a curd has formed, and mixture doesn’t flow readily when container is tilted. (It may also form smaller curds suspended in clear liquid.) The process takes 18 to 24 hours. If some clear liquid has risen to the top of the milk during this time, stir it back in. If liquid has turned light pink, discard batch and start again.
  3. Once curd has formed, stir in flour until smooth. Cover tightly and let stand in a warm place until mixture is full of bubbles and has a good sour smell, 2 to 5 days. Again, if clear liquid forms during this time, stir it back into starter. If liquid turns pink, start over. To store, cover and refrigerate.

Care and feeding of your starter

To keep bacteria and yeasts healthy, the yogurt starter must be nourished occasionally with flour and milk.

Environment. When creating the starter, incubate it between 80° and 90°. Any hotter and the bacteria may die; any cooler and the starter could develop mold. Set it on top of your water heater, on a counter with a lamp warming it, or in an oven warmed with pans of boiling water. An established starter is stronger; after feeding, it can stand at room temperature.

To feed the starter and keep it going. For best results, try to feed the starter at least once a month, even if you’re not baking. To feed, add warm (90° to 100°) nonfat or low-fat milk and all-purpose flour to the starter, each in quantities equal to what you’ll be using in the recipe. For example, if the recipe calls for 1 cup starter, add 1 cup milk and 1 cup flour. (This is also the right amount for a monthly feeding even if you’re not baking.) Cover tightly and let stand in a warm (80° to 90°) place until bubbly and sour-smelling and a clear liquid has formed on top, 12 to 24 hours. The clear liquid shows that the acid level has risen and is starting to break down milk protein, and high acid means sour flavor. Use at this point (just give it a stir first) or cover and chill.

To increase the starter supply (for gift-giving or quantity baking), you can add up to 10 cups each of milk and flour to 1 cup of starter (use a large container). The mixture may need to stand up to 2 days before the clear liquid forms on top.

Sourdough starter FAQs

What if I neglect my starter?

Even with the best intentions, it’s easy to forget to feed a starter, but they can be surprisingly resilient. If you rediscover yours in the back of the fridge, take its “pulse.” An “old” smell, no bubbles at room temperature, a top layer of dark brown liquid, or slight mold growth indicate your starter isn’t feeling its best. First spoon off and discard any mold, then stir the starter. Feed it 1 cup each of flour and milk and let stand as directed in To Feed the Starter and Keep It Going, left. After 24 hours, discard half the starter and repeat feeding and standing. Repeat a third time, if needed, until the starter bubbles and has a “fresh” sour smell. If, after repeated feedings, your starter still smells “off” and won’t bubble, throw it away. Also begin a new starter if mold growth is heavy.

Can you use a starter too often?

Overuse isn’t a problem per se; if you bake several times a week or feed your starter a lot all at once (to increase quantity), it may take longer than usual to regain normal sourness. After feeding, let it stand as directed in To Feed the Starter and Keep It Going, left.

Why do starters “die”?

The longer a starter stands without new food, the higher the acidity gets; too much acid, and beneficial bacteria can’t survive. Mold infestations may also kill off good bacteria.

Can I freeze it when I’m not going to use it for a while?

Starters generally freeze successfully for up to a few months, but freezing does change the bacteria’s cell structure. Longer freezing brings more changes and decreases the chance of success with the thawed starter.

Source: Sunset

How Information Enters Our Brains

Lisa Owens Viani wrote . . . . . . . .

We may have less control over our thoughts than previously assumed.

Think you’re totally in control of your thoughts? Maybe not as much as you think, according to a new San Francisco State University study that examines how thoughts that lead to actions enter our consciousness.

While we can “decide” to think about certain things, other information — including activities we have learned like counting — can enter our subconscious and cause us to think about something else, whether we want to or not. Psychologists call these dispositions “sets,” explains SF State Associate Professor of Psychology Ezequiel Morsella, one of four authors on a new study that examines how sets influence what we end up thinking about.

Morsella and the other researchers conducted two experiments with SF State students. In the first experiment, 35 students were told beforehand to not count an array of objects presented to them. In 90 percent of the trials, students counted the objects involuntarily. In a second experiment, students were presented with differently colored geometric shapes and given the option of either naming the colors (one set) or counting the shapes (a different set). Even though students chose one over the other, around 40 percent thought about both sets.

“The data support the view that, when one is performing a desired action, conscious thoughts about alternative plans still occupy the mind, often insuppressibly,” said Morsella.

Understanding how sets work could have implications for the way we absorb information — and whether we choose to act or not. We think of our conscious minds as private and insulated from the outside world, says Morsella. Yet our “insulation” may be more permeable than we think.

“Our conscious mind is the totality of our experience, a kind of ‘prime real estate’ in the cognitive apparatus, influencing both decision-making and action,” Morsella said.

The new study demonstrates that it’s actually quite easy to activate sets in people and influence what occupies the brain’s “prime real estate.”

“The research shows that stimuli in the environment are very important in determining what we end up thinking about and that once an action plan is strongly activated its many effects can be difficult to override,” said Morsella.

The study’s findings support Morsella’s passive frame theory, which posits that most thoughts enter our brains as a result of subliminal processes we don’t totally control.

Source: San Francisco State University

Cinnamon May Help Battle Infections

Tim Newman wrote . . . . . . . . .

Concerns over antibiotic resistance are reaching fever pitch, and the race is on to uncover novel compounds to replace them. A new study suggests that cinnamon might offer a helping hand.

Since their first use, antibiotics have saved countless lives. Now, however, the tide is turning.

Over countless generations, a growing number of bacterial species have built up resistance to antibiotics.

This means that infections that were once easy to treat are now impervious to antibiotics. It is a growing global problem.

In fact, the World Health Organization (WHO) refer to the antibiotic resistance crisis as “one of the biggest threats to global health, food security, and development today.”

For these reasons, it is vital that we find other ways of effectively tackling infections without using antibiotics.

Cinnamon investigated

Dr. Sanjida Topa and her colleagues at Swinburne University of Technology in Australia have been investigating traditional medicines. Most recently, they looked at cinnamon.

They focused on this particular spice because, as Dr. Topa explains, “many previous studies have reported antimicrobial activity of cinnamon essential oil, [but] it is not widely used in the pharmaceutical industry.”

In particular, they concentrated on a component of cinnamon oil called cinnamaldehyde (CAD), which is responsible for cinnamon’s distinctive taste and aroma. Their findings were published recently in the journal Microbiology.

The researchers wanted to test whether CAD could break up biofilms, which are sticky layers that are often responsible for persistent infections that even antibiotics cannot touch. The most well-known example of a biofilm is the plaque found on teeth.

In order to congregate and form into biofilms, bacteria must communicate with each other to build this complex structure. The researchers wondered whether CAD might disrupt this highly orchestrated event.

“We hypothesized that using natural antimicrobials, such as essential oils, might interfere in biofilm formation. Thus, we focused on the impact of different concentrations of cinnamaldehyde in different biofilm development stages.”

Breaking up biofilms

For their experiments, they used Pseudomonas aeruginosa, a bacterium commonly responsible for infections in people with reduced immune systems, such as individuals with cancer, diabetes, or cystic fibrosis.

When CAD was tested against bacterial biofilms, it was shown to break them down in over three quarters of cases. It also appeared to hinder the formation of biofilms and prevent bacteria from spreading.

Biochemical analysis showed that the disruption of biofilm genesis was likely due to reduced levels of a second messenger called bis-(3′–5′)-cyclic dimeric guanosine monophosphate, which is known to be important in their formation.

“These findings definitely contribute to the search for novel antimicrobials. […] Fabrication of cinnamaldehyde for surface treatments, for example [to treat] skin infections, could be the first direct application.”, said Dr. Sanjida Topa

As Dr. Topa explains, “Humans have a long history of using natural products to treat infections, and there is a renewed focus on such antimicrobial compounds.” Hopefully, this approach will help restock our arsenal of antimicrobial agents as antibiotics become increasingly toothless.

Source: Medical News Today

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