Rachel
- Feb 27, 2023
- 34 min read

The Science of Bread (Part 5) - The Science of Salt Rising Bread / Salt-Rising Bread

Let me introduce to you Salt-Rising Bread (or salt rising bread), a bread made by bacteria that can ferment cornmeal and potatoes...and also cause gas gangrene and food poisoning! This bread is not made with yeast or lactic acid bacteria (well maybe some lactobacillus bacteria), instead the primary fermenter is Clostridium perfringens. A 'cousin' to Clostridium botulinum, the bacteria that causes botulism. However, C. perfringens makes some of THE most cheesy and delicious bread I have had in my life. Is this worth the risk? The links to the video are below, followed by my notes, information, and references I used to make the video.

Video Link: https://www.youtube.com/watch?v=5bG0wK5IGG8

Feel free to check out the other bread science videos:

Part 1 - Introduction to Bread Science: Citations and References ; YouTube video

Part 2 - The Bread Making Process: Citations and References ; YouTube video

Part 3 - The Science of Sourdough Bread: Citations and References ; YouTube Video

Part 4 - The Science of Rye Flour and Rye Bread: Citations and References ; YouTube Video

The Salt-Rising Bread Recipe with Cornmeal Starter

The Salt-Rising Bread Recipe with Potato Starter

Bread Science 5 – The Science of Salt-Rising Bread (Salt Rising Bread)

Slide 1 – Title Slide

Would you be interested in eating a bread with cheesy flavor notes, similar to that of Swiss, Parmesan, or aged cheeses like aged cheddar? You’re probably thinking, hmm that sounds good.

Well, would you still be interested in eating this cheesy bread if it was made with a bacteria that causes diseases such as food poisoning and gas gangrene? I can only imagine what you’re thinking, probably this bread is the last thing you’d be interested in.... However, today I hope I can convince you that this cheesy, but potentially dangerous bread is 100% worthy of your tastebuds. Truly.

Hello everyone, I know it’s been a while but I am back with a new bread science video. The topic today is Salt-rising bread, which is something you may not have heard of before. Salt rising bread is made using a method that could poison or kill you, but the reward is a uniquely delicious and cheesy tasting bread. I hope that has piqued your interest.

You may notice the length of this video (and blog post), it is a doozy, it is so very long. But I really got obsessed with discovering the science behind this bread. And I hope that if you have time to kill you may become fascinated with this bread that could, well, potentially kill you.

Slide 2 - Disclaimer

Always fully bake your bread, etc.

Slide 3 - potato video

I want you to take a look at this video for a few moments, and wonder what may be going on here.

What does this bubbling mysterious jar have to do with bread?

Well, it’s one of several ways to culture a dangerous bacteria for making delicious bread.

Like me, salt rising bread is distinctly American. This bubbling jar is part of a pretty gross process that generates loaves very flavorful bread.

To be perfectly clear, this bread is made without any yeast. And it is not sourdough. And it is not risen by salt, despite the name “salt rising bread”

So, if you are not overly sensitive to the darker sides of food microbiology, then I suggest you stick around and find out what this bubbling jar has to do with bread.

Slide 4 – picture of spoiled potatoes/corn

Have you ever had food spoil in your refrigerator or kitchen? Well, have you ever thought about making some bread with it?? Well, maybe you would consider making banana bread with overripe bananas, but, I bet you don’t consider making bread with rotting corn or potatoes. Well in today’s case of salt rising bread, we will be using spoiled corn and potatoes😊

Slide 5 – Outline

Alright, here is the outline for this presentation, and I will include time stamps in the description below for each section. First we’ll start with…

Part 1: Introduction to SRB - Which includes Brief Yeast and Sourdough refresher

Part 2: Salt-Rising Bread: History and Context - Is it really leavened with salt?

Part 3: Bacteria-Rising Bread - How a deadly bacteria makes delicious cheesy bread

Part 4: The Salt-Rising Bread making experience

Part 5: A Deadly and Dangerous Experiment

Conclusion

Slide 6 – Part 1: Introduction

Slide 7 - Yeast and Sourdough refresher, chemical leaveners, and SRB

Before we get into the world of making bread from spoiled food, we first have to position ourselves in the world of bread. We live in a modern world where bread loaves are primarily made with mass produced yeast, or with sourdough. But salt-rising bread is distinct from these breads.

I do have other videos covering yeast breads and sourdough bread, but here’s a brief refresher so you can understand why salt rising bread is different from these breads.

In commercial yeast and wild yeast (sourdough) breads, we have sweetness from enzymatic breakdown during fermentation. The yeast break down starch and sugars, making the bread sweeter. This starch breakdown also makes ethanol that flavors the bread. The fermentation also creates CO2 that lifts the bread and forms bubbles, making it light and soft. Sourdough usually contains wild yeast, while commercial yeast breads primarily have one type of yeast.
Alongside wild yeast, sourdough contains lactic acid bacteria (LAB) that ferment and break down starch and sugars, producing lactic acid and acetic acid which creates more complex flavors and acidity. LAB can also produce CO2 in some cases.
Sometimes bread is leavened with chemical leaveners, which became popular in the 1800s because chemical leaveners are faster than yeast. These breads are often called quick breads. An example is Irish Soda Bread. The chemical leavener baking soda reacts with acid in the dough to make CO2, which makes the bread rise. Usually these breads brown nicely, but don’t have fermented flavors.

So, to be clear, salt rising bread is not leavened with yeast, lactic acid bacteria, or chemical leaveners. It is fermented, but it is a different kind of bread than these others listed. Yeast and lactic acid bacteria aren’t the only microorganisms that can create gases, flavor, and lift in bread. There are other bacteria that can do the same.

4. Salt rising bread is fermented and leavened by a particularly disturbing bacteria. This bacteria can ferment sugar and starch like the yeast and LAB, but the products of this fermentation are both different, and a lot stinkier. The flavor of salt rising bread is quite different from commercial yeast or sourdough breads.

Slide 8 – What is Salt-Rising Bread?

Salt-rising bread is made by fermenting a starch like potato and/or cornmeal under specific conditions.

The starter can be made with potato or cornmeal, or a combination of both. Here, I show examples of a potato starter bread in the top row of pictures, and the cornmeal starter bread in the bottom row of pictures.
To create salt rising bread starters you first need to kill, or reduce, the yeast and lactic acid bacteria populations. You do this by pouring very hot, or boiling liquid over the potato or cornmeal. This allows new bacteria to colonize the starter once it has cooled down. If you are successful, you will get the right kind of bacteria in your starter for salt rising bread. You might be able to see the fermentation bubbles in these photos.
The primary bacteria in these starters is Clostridium perfringens, and you’ll know you’ve been successful because you will feel like you can smell the starter from a mile away (or 1.6kms away). Clostridium perfringens, which I will often refer to as C. perfringens, uses the starch, sugar, and proteins in the potato or cornmeal as food to grow and multiply rapidly. The starters are stinky because of how C. perfringens ferments these food sources.
So, essentially, salt rising bread starters are made by controlled rotting.
So when this first jar is bubbly, active, and stinky (in a bad way), this means you have a strong C. perfringens population in the starter. But a big population means it needs more food to continue fermenting, so next you add flour as a food source, and do a second fermentation (second pictures), Hopefully, you can see how bubbly and active the starters are in the second photos after the second fermentation (indicate).
After the starters are bubbly again, then you can make them into bread (3rd and fourth pictures). And bake the loaves. Despite how stinky the starters and dough are, the resulting bread has cheesy flavor notes, and this bread is fantastic with butter!

Slide 9 – What is salt rising bread continued

You can just read the slide (note to self)

Slide 9 – Part 2: Context and history

Slide 11 – History

First, I want to acknowledge that there is no complete history of salt-rising bread. But all the resources I can find indicate that SRB is a distinctively American bread tradition.
It was a unique way of making bread that began among settlers of the Appalachian Mountains of the United States of America in the 1800s. It is occasionally found in bakeries in Appalachia in the modern day, but it is rare.
Salt rising bread was likely invented due to yeast scarcity. In the 1880s, Appalachian settlers may not have had access to fresh yeast while travelling and settling. In addition, fresh yeast spoils quickly and shelf stable commercial yeast wasn’t invented until the late 1800s.[1] Obviously sourdough had been around for thousands of years, but the settlers may not have been able to reliably maintain a sourdough starter.[2] Therefore, they decided to get creative.

Slide 12 – Why “salt” rising?

So why is it called salt rising bread and not gross bacteria bread?

Well, the settlers didn’t know they were harboring a dangerous bacteria in their salt-rising starters, microbiology was not an advanced field in the 1800s (like it is today). But, one of the reasons it may have been called salt-rising bread is because the starters may have been kept in warmed rock salt beds while the settlers travelled, where the warmth encouraged fermentation and bubbly bread.[1][20]
Another reason it may be called salt-rising is to indicate that it is not 'yeast-rising' bread.[1][2] So, to differentiate the two types of bread.
In addition, another reason it may be called salt-rising bread is because it may have originally contained different salts, like potash, which is a potassium rich alkaline salt that was historically used in baking in the United States, but was eventually forgotten in favor of saleratus, which was the precursor to baking soda, and then replaced by baking soda that we still use today.[20]

Slide 13 – Potash – Rise and Demise

I wanted to go a little more in depth on potash.

Historically, potash (pink material on the right) was used in some German and Dutch baking. So it’s earliest known uses in American baking were with Dutch settlers in New York in the 1700s.[21] It helped breads rise much faster than when they were made with yeast.
By the 1830s, potash was a common baking ingredient in cookbooks.
As time went on, new products like baking soda and baking powder became popular, and because Potash was difficult to produce it was replaced by these other chemical leaveners.[23] In part 4 of this presentation the recipes I use for salt rising bread both include baking soda, but in the 1800s it is more likely that potash or saleratus were used, so these chemical salts may be why the bread was called “salt-rising.”
Nowadays potash is primarily used in fertilizer production, but potash is still used in baking in some countries like Germany and Denmark. There are some examples on the right hand side here.

So in summary, in the 1800s Appalachian settlers likely thought it was chemical salts that explained how the bread rose. They probably had no idea it was actually a deadly bacteria.

Slide 14 - But what is ACTUALLY rising this bread?

It was not known that salt-rising bread was encouraging the growth of pathogenic bacteria until 1923 when a USDA microbiologist, Stuart Koser, was analyzing salt-rising starters.
Koser discovered that the starters were full of the Clostridium perfringens bacteria (which was formerly known as Bacillus welchii).[2]
Koser also performed some gruesome experiments to confirm his findings.[2] There’ll be more on these experiments in part 5.

Slide 15 – Part 3: Bacteria-Rising Bread

In this section I will discuss the primary bacteria behind salt rising bread - Clostridium perfringens.

Slide 16 – Bacteria-Rising Bread: C. perfringens and others

Although C. perfringens is the primary bacteria that is fermenting and rising the bread, there may also be a lactic acid bacteria (LAB) community and other bacteria present.

There are very few studies on salt rising bread, the completed studies all indicate that C. perfringens is the main bacteria, so I will be focusing on it.

Slide 17 - What is Clostridium perfringens bacteria?

C. perfringens is the dangerous parent of a delightfully cheesy bread.

Scientifically it is a gram-positive, rod shaped bacteria.
It is pathogenic and can release toxins.
It does best in anaerobic (no-oxygen) conditions.[3] When oxygen is present, C. perfringens can form endospores to survive this aerobic condition, where it waits until conditions are right so it can germinate into an active living cell again.
C. perfringens is ubiquitous, meaning that we find it almost everywhere. It’s in soil, water, food, healthy and unhealthy gut microbiomes, feces, and marine sediment, for example.
C. perfringens' role in the environment is to help decompose dead organisms like plants and humans, so it’s a useful decomposer in our environment.[3] But sometimes it infects living organisms, which can be very problematic.

Slide 18 – Growth conditions

C. perfringens has some ideal Growth conditions:

Temperature range: 15-55°C (59-131°F)
Optimum Temperature: 43-47°C (109-117°F)
pH range: 5-9
Salt Tolerance: 5%[5]

Slide 19 – Strains of C. perfringens

There are 5 strains of C. perfringens, A, B, C, D, E

Today we will primarily be focusing on strains A and C because they cause important diseases in humans, which can be fatal.

C. perfringens can form spores that can release disease-causing toxins in the human body.

Slide 20 – What is a spore?

Here is a picture of a C. perfringens spore, although the scientifically correct term for this is an endospore.

Why am I using both terms (spore and endospore)? Well, a lot of the literature states that C. perfringens forms spores, but the correct term is actually endospore, because an endospore is a non-reproductive cell while a spore is a reproductive cell associated with other forms of life, such as fungi.[32]
But since science seems to use spore and endospore interchangeably, I will too in this presentation. I will often talk about C. perfringens spores, but I really mean C. perfringens endospore.

But, what is an endospore?

An endospore is a bacteria in a highly protected state that resists harmful environmental conditions.
C. perfringens can form spores to protect itself from stressors like: high temperatures, aerobic conditions, ultraviolet radiation, desiccation, extreme freezing, and chemical disinfectants.[30] Bacterial spores are not impossible to kill, just very difficult to kill, especially in food.
Once living conditions are preferable again and the spore is warm and happy, it can germinate into a living, or vegetative cell.
Spores form via the process of sporulation. Sporulation triggers the release of disease-causing toxins. This is important!

Slide 21 – C. perfringens sporulation and toxin formation

In most cases, C. perfringens can only release toxins that cause disease if it first goes through sporulation, which is the process of becoming a spore.

I am about to show a complex diagram on C. perfringens sporulation, but I am only going to describe the most important details so you can understand what I mean. (See diagram)
Okay, first let’s focus on the left-hand side of the figure. Here we have a C. perfringens bacteria going through normal reproduction, known as binary fission.
But, if the C. perfringens is stressed by it’s environment, then it will not go through normal binary fission, instead it will go through the process of sporulation. In sporulation, the cell divides into two sections, which include the mother cell and pre-spore. The mother cell then covers the pre-spore in protective layers before splitting open and releasing the finished spore into the environment.
So a spore is essentially a protected version of the cell. Once the environment is no longer stressful, the spore can germinate, and become a living active cell again.
The important thing that I will highlight in red (in the video), is that the cell forms toxins as it begins the sporulation process (likely in response to the stressful environment), and it releases those toxins when the mother cell splits open to release the spore. It's like a defense mechanism to make sure the cell survives.
So, toxin formation and release happens when C. perfringens is stressed and forms a spore, and this is what makes spores so dangerous.

Slide 22 - Foodborne illnesses caused by C. perfringens

C. perfringens can cause two foodborne illnesses.

1) Food poisoning. C. perfringens is one of the most common causes of food poisoning.[3] Food poisoning is caused by Strain A C. perfringens that release an enterotoxin.

If you eat food that contains a lot of living C. perfringens or C. perfringens spores, you can get sick with food poisoning. The bacteria can be an issue whether you eat the food raw, don’t cook it enough, or even if you fully cook it. This is because some spores can survive cooking temperatures. Another reason food can become contaminated is if it is improperly stored and kept warm after cooking/baking.
Strain A C. perfringens can only release the enterotoxin that causes food poisoning if they become spores (via the process of sporulation). This is very important. What’s also important is that the spores that Strain A form are highly resistant to environmental stress, such as cooking temperatures and the body’s defense mechanisms in the human digestion system.
Digestion figure: So, lets imagine that this person is consuming lots of spores and living cells of C. perfringens. The human digestive system is a stressful environment and it may destroy some of the spores and living cells. However, some spores may survive, and the living cells may have gone through sporulation because of the stress exerted by the digestive system. If these spores make it to the small intestine they can release enterotoxins generated during sporulation, and the enterotoxins cause diarrhea and food poisoning.

Slide 23 - Foodborne illnesses caused by C. perfringens

The second foodborne illness caused by C. perfringens is:

2) Pigbel Enteritis necroticans (pigbel) is caused by Strain C C. perfringens that release β-toxins

The process for a C. perfringens pigbel infection is very similar to food poisoning, but pigbel can be much more serious. Essentially, pigbel occurs when malnourished people eat food containing a lot of C. perfringens bacteria, i.e. Strain C C. perfringens. Like with the food poisoning, the living C. perfringens can form spores in the human body, and the spores can resist the first stages of digestion.
Once in the intestines, the spores can germinate and secrete β-toxins that cause tissue death in the intestines.
So pigbel can be a lot more dangerous and deadly than food poisoning caused by Strain A C. perfringens. This disease is rare in developed countries.

Slide 24 – Another illness caused by C. perfringens – Gas gangrene

3) Clostridial myonecrosis (gas gangrene) is caused by Strain A C. perfringens that release α-toxins and perfringolysin O (PFO) - toxin that destroys human cells

Wait, doesn’t Strain A also cause food poisoning? Yes, but food poisoning is caused by enterotoxins, while gas gangrene is caused by α-toxins and PFOs.
If we break down the word myonecrosis, it means muscle death, or death of muscle tissue. Gruesome.
Gas gangrene is an infection where spores or vegetative cells of Strain A C. perfringens enter the body through a wound and infect muscle tissue. You’ll notice that spores are again important in the infection process, which is similar to how C. perfringens causes food poisoning and pigbel. However, they enter through different parts of the body, e.g. the open flesh / wounds.
After C. perfringens enters the body through a wound, it grows and reproduces in the muscle tissue, it generates gas, and releases those α-toxins and PFOs. The α-toxins and PFOs insert into the plasma membrane of cells, disrupting cellular function[3], causing muscle tissue and soft tissue death.[36]
Visibly the gas production and toxins released can lead to large blisters and jaundice.[3] I have a diagram of what severe gas gangrene can look like. Gas gangrene spreads quickly in the body, making it highly lethal.[36]

Slide 25 – Strain type and toxin formation summary table

Furthermore, immunocompromised, sick, young, and elderly people are more susceptible to a C. perfringens infection than healthy people.

Here is a handy table to summarize the toxins for the three diseases I talked about that are caused by C. perfringens. It includes the disease, strain that causes it, and how the infection starts in the body.

It’s important to see that the star(*) means that this toxin is the critical toxin for virulence, that is, the C. perfringens has to produce that toxin, or toxins, to actually cause that disease.
As you can see, all strains produce the alpha-toxin, but when Strain A produces it along with PFO toxins, it can cause gas gangrene.
In order for strain A to cause food poisoning it has to release enterotoxins, which is it’s critical toxin for virulence, meaning that it needs this release toxin to cause food poisoning.*
Then we have strain C, which causes pigbel if it can release the beta-toxin, which is it’s critical toxin for virulence.

Slide 26 – Summary on C. perfringens diseases

So, there are three big takeaways from the previous slides

There are different strains of C. perfringens that cause different diseases depending on the toxins that they release
Spore-formation often leads to toxin formation and release in the human body (this will be relevant in part 5)
C. perfringens can be deadly, but it can also make delicious bread

Slide 27 - C. perfringens metabolism

Sure, C. perfringens could kill you, and I’ve talked about the diseases it can cause, but for today's bread science video it’s more relevant to look at this bacteria’s primary metabolic pathways to understand what it eats, and how it survives in the environment it lives in. That will provide insight into how it leavens salt-rising bread.

I will focus on a few metabolic pathways of C. perfringens:

During anaerobic respiration, C. perfringens gains energy by breaking down complex carbon compounds and uses nitrate as an electron acceptor.
During fermentation, C. perfringens breaks down sugars, similar to how yeast breaks down sugar, but instead of producing CO2 and alcohol (ethanol) like yeast, C. perfringens primarily produces CO2 and Hydrogen gas. Similar to yeast, C. perfringens can produce ethanol, but it does not typically produce ethanol.[29] Furthermore, C. perfringens fermentation often produces volatile acetic acid, acetone, butanol, and butyric acid, all of which create potent, unpleasant smells.[18] So that’s part of why the starters stink.
C. perfringens can cause milk to spoil by metabolizing lactose (perform lactic acid fermentation) into lactic acid and gas[19], [25]. It can do this because C. perfringens possesses the enzyme β-galactosidase (as well as α-galactosidase[26]).
C. perfringens could technically spoil milk at anytime if there are enough C. perfringens present and the temperature is warm, even if it the milk has been pasteurized. This is because the lactose sugars are not destroyed when the milk is pasteurized, and because C. perfringens can form spores at high temperatures. Contaminated milk can be avoided by good farming practices (not contaminating milk), physically removing endospores, using preservatives, or antimicrobial treatments, and refrigerating milk.[37]

[28] image

This will sound similar to fermentation, but C. perfringens has the entire set of enzymes necessary to perform glycolysis and glycogen metabolism[26], where C. perfringens breaks down sugar compounds into simpler forms to gain energy.[17] C. perfringens can use fructose, galactose, glycogen, lactose, maltose, mannose, raffinose, starch[28], and sucrose.[26] C. perfringens possesses various genes for glycolytic enzymes, such as α-galactosidase, β-galactosidase, α-glucosidase, β-glucosidase, β-glucuronidase, β-fructofranosidase (sucrase), α-mannosidase, pullulanase, α-amylase, and endo-1,4-beta-xylanase.[26]
The fact that C. perfringens can break down a variety of starch and sugars is especially important in the salt rising bread making process that starts with potato or cornmeal, and sometimes includes milk.
When C. perfringens metabolizes amino acids and fatty acids it can produce foul-smelling degradation products.[18] I will talk more about this in part 4.
C. perfringens may be able to perform proteolysis[38], [39], or the breakdown of proteins, which could be relevant for the gluten in salt rising bread as evidenced by research done in intestines, where they discovered a C. perfringens breaking down proteins to extract nitrogen--critical for it’s survival.

Overall, the byproducts of C. perfringen’s metabolism will hopefully help you imagine how smelly and unpleasant it can be to make bread with this bacteria.

Slide 28 - Part 4: The Salt-Rising Bread Making Process

Slide 29 - How do you make salt rising bread?

In the recipes I show today, I made two separate bread with a potato starter and cornmeal starter. I’ll start with the potato starter bread.

Slide 30 - First, the potato starter

The first photo is of the ingredients I used.

When making the potato starter, I sliced an unpeeled russet potato and added it to a jar along with some flour and a little bit of sugar, baking soda, and salt. I think the sugar, flour, and potato all act as food sources for the bacteria since it can ferment the potato starch and sugar and perform glycolysis.

Traditionally the baking soda and salt were likely used to help leaven the bread and add flavor, respectfully. I am not sure if the baking soda is an essential ingredient, but I added it to stay true to tradition. But, when I though bit deeper about the salt and baking soda, I think they could be helping to control the fermentation. Firstly, baking soda can help leaven bread by generating CO2 when it reacts with the acids produced during fermentation. Secondly, baking soda is also alkaline, so it can buffer, or raise, the pH while the fermentation generates acids and CO2. If we remember from earlier, the ideal pH for C. perfringens is between 5 and 9, to the baking soda may prevent the starter from becoming too acidic for C. perfringens.
Meanwhile, the added salt may be controlling fermentation by slightly reducing the activity of the microbial population (e.g. by influencing osmotic pressure). The salt also helps with gluten formation. And since C. perfringens may be breaking down the gluten, the salt may be extra important.

Slide 31 – Potato starter: Add boiling water

Alright, back to the starter. Next you will see in this video that I am pouring boiling water over the ingredients, covering them. In microbial activity terms, the boiling water is essentially a catastrophic event. Since the water is 212°F (100°C), it kills the yeast and lactic acid bacteria that may be present (because yeast are killed at 140°F, and LAB are typically killed at 145 to 160°F).[2] This step prepares the starter for C. perfringens to enter the starter and grow once the starter has cooled! It is literally that “it’s free real estate” meme for C. perfringens.
It is also possible that the boiling water is triggering spore formation of pre-existing C. perfringens bacteria in the potato (and also in the cornmeal starter), and that they will germinate once conditions are right again. It’s kind of cool to think about, right?
After the boiling water is added, I covered the starter with plastic wrap and poked a hole in the top so new bacteria could enter and so the starter can offgas while it ferments.

Slide 32 - Potato Starter - Fermenting the potato starter

After adding that water I let the potato starter ferment in a very warm environment of 100-110°F or 37-43°C for 8-12 hours. The environment needs to be quite warm, which isn’t a coincidence. This starter ferments fastest at body temperature, or at fever temperature because that’s usually the best temperature for Clostridium perfringens to grow and reproduce in the human body!
How did I create such a warm environment? Well, my oven with the light on was not warm enough. So I created a hot environment with a wax warmer and cardboard box. It wasn’t a perfect setup, but stayed around 98-104°F, or 37-41°C.
During this fermentation the potato starter slowly began to bubble and produce gas. It started to smell as if it was going bad, that is, rotting or putrifying. This is good though! The smell was hard to describe. It was like a deep funky, and pungent foul smell. Perhaps if I had more experience with different kinds of rotting food, or more experience in tasting strong cheeses, then I could describe the smell better. It was like an overripe smell, sort of similar to stinky feet.
The potato starter also began to look different as it fermented, with the liquid turning from clear to cloudy and yellow. Bubbles were very apparent by the end of this first fermentation.

I do want to note that the potato starter and the cornmeal starter are not guaranteed successes. This is a matter of trial and error in some cases, and you don’t want to make these starters in environments that are too clean.

Slide 32 – Potato Starter after first fermentation

Slide 33 - Potato starter - Ingredient addition and second fermentation of the starters

During this first fermentation the bacterial population explodes and now it needs more food.

So, first you discard the solid material, but reserve the liquid from it.
Then you mix in warm water and flour (the flour is more food for the bacterial community) and the warm water is making the C. perfringens happy.
Let it ferment a second time, until doubled in size. This is essentially a second starter, or pre-dough. This second fermentation takes about 2-4 hours. You may notice the putrid smell growing stronger, because the bacterial community is growing and generating more volatile compounds.

Slide 34 – Close up after second fermentation

Look at those little bubbles

Slide 35 - Potato Starter - Final dough mixing and final fermentation

After the second fermentation, the community once again needs more food. So more flour is added, enough to make a bread dough. It is then kneaded into a smooth dough.

Slide 36 – Potato Starter: Final Fermentation Baking!

Then I shaped the kneaded dough into the loaf pan and let it rise one final time, in that warm wax warmer environment for about 2-4 hours, until about doubled in size

After this third and final rise, this stinky loaf is finally ready to bake! As you can see, the loaf did not get much oven spring, but my kitchen smelled very funky as it baked.

Slide 37 – Potato Starter: Finished bread and taste

What does it taste like?

The salt rising bread made with the potato starter smells like a funky cheese. It has a pungent flavor as well as smell. If I was a more experienced cheese taster I could probably suggest some cheeses it reminds me of. Maybe a bit like Swiss cheese? It kinds of “gas bombs” your mouth as you eat it, similar to the effect that blue cheese has on me. It does taste slightly off, or spoiled, but not in inedible or overwhelming way. It also tastes a little like saltine crackers, or soda crackers, maybe due to salt and the baking soda. I recommend adding some butter to a slice, this makes the eating experience much more enjoyable and creates more well rounded flavors.
Another thing that surprised me was that this bread has quite a crumbly texture, which makes it different from many yeast breads I make. It’s almost more like a firm cake than a normal soft yeast bread. Also, the gluten structure feels different. I’m guessing that’s because we have a different fermentation community than in yeast bread.

Slide 38 - Cornmeal Starter - Making the cornmeal starter

So now we move onto the cornmeal starter bread! The recipe I tried has more ingredients than the potato starter bread, but the process for making both breads is similar.

To make the cornmeal starter, I combined cornmeal and sugar together in a jar.

Next I scalded some milk by heating it to 170-180°F (77-82°C) and poured it over the starter. The cornmeal, milk, and sugar are food sources for C. perfringens fermentation.

Slide 39 – Cornmeal starter – Adding scalded milk

As soon as the milk is scalded, I poured it over the cornmeal mixture. This process kills most lactic acid bacteria (most LAB are killed at 145°F to 160°F[20]) and yeast present, but primes the environment for C. perfringens, which can use the cornmeal starch and sugars and lactose in the starter as food.[18] We did a similar thing when adding the boiling water to the potato starter.
So this starter uses milk, which the potato starter did not include. And the milk made a pretty big difference in the smell of the first starter and the taste of the final bread. I think this is because C. perfringens can do lactic acid fermentation with milk in the cornmeal starter, but not with the potato starter. This first cornmeal starter definitely smelled more like cheeses I am familiar with than the potato starter did.

Slide 40 – LAB can inhibit C. perfringens

If the milk in the cornmeal starter can stimulate C. perfringens lactic acid fermentation, could the milk also make it friendly to the lactic acid bacteria in the environment? Probably. Even if you scald the milk and destroy the LAB community, new LAB can enter the cooled starter and ferment the intact lactose. I mentioned earlier that some of my online research indicates that SRB starters can contain LAB; however, there should also be stronger and larger community of C. perfringens present as well.
We don’t want LAB to compete with C. perfringens in salt rising bread starters. In fact, there’s some research where LAB can be purposefully used to inhibit C. perfringens growth, such as in cheese making, or in preserving things like olives or meat to prevent C. perfringens infection.

You will know if your starter has a dominant C. perfringens community based on the stinky smell. It shouldn’t smell like yogurt or buttermilk, but instead like feet or strong cheeses.

Slide 41 – Cornmeal Starter: First Fermentation

Back to the starter, After adding the scalded milk you cover the starter with plastic wrap, and poke a hole in the top, and place it in a very warm place (the same as the potato starter) for 8-12 hours.

During this time, the starter should hopefully become smelly and bubbly. In my case, the starter had a cheese-like smell, that is, it smelled like swiss or parmesan cheese.

Slide 42 - Cornmeal Starter – To germ or not to germ

On a brief tangent, some SRB recipes insist it is best to use nondegerminated cornmeal, that is, cornmeal with an intact germ, rather than degerminated cornmeal in the cornmeal starter. I think the reason people think having the germ is important is because the germ has a lot of vitamins that can help the microbial community grow.[16] But honestly, I tried the recipe with both types of cornmeal, and both types of cornmeal worked, and the degerminated cornmeal actually seemed to work better.
I used a few brands to test whether germ was important, and to see if finely ground cornmeal made a difference. I used Unico (a degermed yellow cornmeal), Gold (cornmeal (doesn’t specify germ)), and Bob’s red mill (made from whole grain corn, (contains the germ), and finely ground).
During the first ferment, the Unico cornmeal starter smelled like Swiss Cheese.
Bob’s red mill brand smelled like cornmeal and milk (not much funky fragrance) .
The Gold cornmeal smelled more like Parmesan cheese.
So clearly, I got more cheese-like fermentation smells from certain brands, so the brand and type of cornmeal you choose will likely influence the flavor and volatile compounds it will generate. So if you’re not having success, try a different brand or a newer bag!
I ended up using the Unico brand for my cornmeal SRB, because it created an active and fragrant starter that smelled like swiss cheese. It made great bread, so even a de-germinated cornmeal can work very well!

Slide 43 - Cornmeal starter - Ingredient addition and second fermentation of the starters

Back to the bread.

After the first fermentation, I didn’t discard any of the cornmeal starter. To the starter I added hot (120-130°F or 49-54°C) water, salt, baking soda, sugar, and additional flour to feed the microbial community and create the second starter.
As mentioned with the potato starter, these added ingredients will affect the fermentation environment and the bread flavor and rise. The flour and sugar are food that trigger fermentation, and the baking soda may be controlling pH or helping the bread rise as acid is produced during fermentation. The salt may also be controlling fermentation.
This second starter is then covered and placed in the same very warm environment (I used the wax warmer environment) to double in size, which takes about 2-4 hours. Mine continued to smell like cheese, but it also started to smell more pungent and slightly unpleasant, similar to the potato starter.

Slide 44 - Cornmeal Starter - Final dough mixing and final fermentation

After the second fermentation is complete, we are ready to make our final dough!
To the second cornmeal starter, I added about 4 tbsp. of salted butter and enough flour to make a smooth bread dough. I do want to acknowledge that the butter did change the flavor and texture of this bread, making the end result more buttery, full flavored, and soft relative to the potato starter bread. But honestly the cornmeal starter bread was definitely my favorite of the two, so if you do try this cornmeal SRB you can omit the butter but it does add amazing, amazing flavor!

Slide 45 - Cornmeal starter - Baking!

The dough is then shaped and fermented a third and final time before baking. While baking, the salt rising bread made with the cornmeal starter gave off this delicious, but potent toasted buttery cheese scent. The butter in the bread made it smell like a buttery delicious grilled cheese in the oven.

Slide 46 - Cornmeal starter – Finished Bread and Taste

So what does this bread taste like?

The flavor of the cornmeal starter bread was truly incredible. It tasted like a combination of cheddar, swiss, and parmesan cheese. Imagine having cheesy bread with no cheese in it. This is it. It has a fuller flavor than the potato starter bread while being less pungent in your mouth. I think the milk fermentation adn added butter definitely boosted the flavor of the cornmeal starter bread relative to the potato starter bread. The texture of the cornmeal starter bread is crumbly and it does have a slight saltine-like flavor, similar to the potato starter bread. I’m guessing that 'saltine flavor' is because of the baking soda.
I think this cornmeal starter bread would definitely please people’s palettes more universally than the stronger and funkier potato starter bread. However, if you add butter or other delicious toppings to either bread, then they’re both delectable!

Slide 47 - Where are these funky cheese smells and flavors coming from?

Alright, I am about to go on another tangent, so let’s go for a ride!

So why does this Clostridium perfringens create such a unique smelling and unique tasting bread? Well, it’s because of the variety of gas and flavor compounds it produces.
C. perfringens primarily produces CO2, like our friendly bread yeast and lactobacillus bacteria do in yeasted breads, but C. perfringens is unique in that it also produces hydrogen gas.[2] The CO2 and H2 help leaven the salt-rising bread. Similar to LAB, C. perfringens also produces organic acids such as acetic acid and lactic acid, however, it also produces butyric acid and propionic acid.
There’s something special about butyric and propionic acid. The butyric and propionic acid may be some of the most important stinky flavor compounds in this bread.[2] Which is why I am taking you down this cheese-related tangent.

Slide 48 – Metabolism Refresher

First, remember that C. perfringens has different metabolic pathways relative to yeast, such as breaking down sugars and sugars in milk, as well as metabolizing fatty acids.

Slide 49 - Butyric acid

Butyric acid is known to impart two types of flavors, rancid flavors, and cheesy flavors.[8] If I tell you that human vomit contains a lot of butyric acid then the rancid part may make more sense.[11] With that in mind, the cheesy flavor part sounds crazy, I know, but sometimes there’s a fine line between the flavors of spoiled milk and cheese.

In the right amounts, butyric acid actually imparts a funky and stinky quality to certain cheeses, dairy products, and fermented foods that people really love.

Butyric acid is associated with the sharp smell in certain cheeses[2] such as feta, cotija cheese, Parmesan, Romano, and goat cheese.[6] So yes, Butyric acid is in the cheeses most of us love, and it’s also in vomit. That’s just how the world works sometimes.

Butyric acid is an important acid in salt rising bread.
Now to describe butyric acid in more detail, Butyric acid is a four-carbon fatty acid. C. perfringens produces butyric acid when it breaks down carbohydrates. Butyric acid is quite volatile, which is why this acid is so fragrant.[9]
I know I mentioned that C. perfringens can cause milk to spoil, but in the case of cheese-making, some cheeses are intentionally inoculated with clostridia spores and fermented in a controlled environment.[7] In circumstances where butyric acid is desired in cheese-making, butyric acid production is done by clostridia bacteria, but not Clostridium perfringens – mainly it is done by Clostridium tyrobutyricum, which literally has “butyric” in it’s name. C. tyroburyricum transforms lactic acid into butyric acid, acetic acid and gases including H2 and CO2.[7] C. perfringens can do something similar, but it is not used in cheese making.

Slide 50 - Propionic acid

Like butyric acid, propionic acid is also a short-chain fatty acid.[13] It is naturally formed in your colon as a digestion byproduct.
Propionic acid is something you will likely smell in a Swiss, or Emmental cheeses.[2] Propionic acid fermentation is responsible for the large holes (known as eyes) in Swiss cheese.[14] This acid has a pungent smell on its own, and it makes cheese aromatic.
Propionic acid fermentation is performed by propionibacteria such as Propionibacterium freudenreichii, that uses lactic acid as it’s main carbon source and converts it to propionic acid, acetic acid, and CO2.[15] P. freudenreichii also can perform lipolysis, which produces important short chain fatty acids that contribute flavor.[15]

Slide 51 – Lypolysis

I mentioned that butyric acid and propionic acid can come from the break down of carbohydrates, but these acids can also be generated from the breakdown of fats.[9]
Butyric acid and propionic acid acids can be generated from fats present in milk. Most of these fats, or lipids, that are found in milk/cheese are in the form of triglycerides. Triglycerides contain three fatty acid groups connected to a glycerol molecule.
What's important here is that when those intact chains are connected in a triglyceride, we don't taste much flavor. The flavor is sort of inaccessible…. But the flavor comes out if enzymes called lipases clip off the fatty acids such as butyric acid, freeing it from the triglyceride and letting us taste it’s flavor! [9]
Lipases are often found in raw milk, or are added during the cheese making process.[9] [10] (picture from [10]) So in a nutshell, lipases perform lipolysis, and make milk more flavorful when it’s used in cheese-making.
It’s possible that C. perfringens could be forming butyric and propionic acid from fermentation, glycolysis, and lipolysis, however, I am not 100% sure if it performs lipolysis in SRB starters.

Something I didn't include in the video:

If I may go on one more short tangent about butyric acid, there is an American milk chocolate controversy related to it. If you’ve ever heard a European describe American Hershey’s milk chocolate as tasting sour, or like vomit, it is thought that this is due to butyric acid. It is suspected that American chocolate brands such as Hershey’s either add, or generate butyric acid when making milk chocolate. You may not notice the sour flavor if you’ve been eating it for decades, but according to many people living in Europe, this makes American chocolate inedible. Hershey’s company has kept its formula and manufacturing secrets to itself, and won’t admit that butyric acid plays any part in their chocolate making process, however, it is possible they generate butyric via lipolysis, or that it is added as a preservative. Either way, it is not known for sure, which is why this is still considered a controversy.[12] I personally think milk chocolate has a spoiled milk aftertaste, which is why I usually go for dark chocolate. ANYWAY, let’s get back to this bread!!!!

Slide 52 - How does SRB affect gluten?

Alight, now onto another, but brief tangent.

When I discussed C. perfringen’s metabolism, I mentioned that C. perfringens may be able to perform proteolysis, or the breakdown of proteins. C. perfringens may be able to break down gluten, but there is little research that I could find to support this.

Sources from 1912 and 1961 casually indicate that the bacteria in Salt-rising bread (SRB) starters have “strong proteolytic action”

Proteolysis may explain why SRB Develops an exceptionally close grain and fine texture
SRB bacteria may break down gluten differently than microorganisms in other breads

Overall there is very little research on what happens to the gluten in SRB, and why the bread texture is different from yeasted bread.

Slide 53 - Does this bread freak you out, would you feel unsafe eating it?

The current, but limited research about salt rising bread indicates that you don’t need to be worried about eating this bread.

But I should acknowledge that there’s historically been some scary experiments done that will definitely make you question the safety of this bread.

Slide 54 Part 5: A Dangerous Experiment

So, if your stomach has been strong enough through this presentation so far, this next part may change your mind.

In the 1800s, when the pioneers of Appalachia were making salt rising bread, they didn’t know what bacteria they were growing in their starters, they just knew it was easy to grow and it made a strongly flavored bread. It wasn’t until the 1920s that scientists discovered the more gruesome side to salt rising bread.

Slide 55 – Here’s where things get a little more gross

Do you remember Stuart Koser from earlier in this presentation? He identified Bacillus welchii (which is now known as C. perfringens) in salt rising bread starters in the 1920s.
However, Koser also knew that C. perfringens was responsible for gas gangrene.
So after he identified this bacteria he decided to do a disgusting experiment to confirm his findings.
To test whether Clostridium perfringens really could leaven salt rising bread, he took a sample from a soldier’s infected gangrenous wound and used it to make a successful loaf of bread.[2] Yeah, I know, it is disturbing. This would not be an ethical experiment to perform in the modern day.
The bread he made with the wound sample was remarkably similar in appearance to salt-rising bread made with potato or cornmeal starters.[2] However, Koser did not record notes on the flavor of this gangrene bread[2], implying that either he did not eat the bread, or perhaps he ate it, but it was not worth making notes about.
Koser not only made the bread, but also tested the pathogenicity of this wound sample in a follow up experiment. In this experiment he injected some of the wound sample into guinea pigs (cue picture 1), and it was fatal to the guinea pigs.[24]

So yes, a gangrenous wound sample suspected of containing C. perfringens can kill guinea pigs, but also make bread (cue picture 2). Just, uh, let that sink in for a minute….

Slide 56 – Is the bread itself fatal?

There are a couple things that Koser did not test.

He did not test the finished bread made from a wound sample for toxicity, so the safety of the finished bread was not determined.
Although he made bread that looked like salt rising bread from a gangrenous wound sample, he did not test whether any salt rising bread starters were deadly to guinea pigs.
Perhaps if Koser had injected a sample from a salt rising bread starter into guinea pigs, they may have survived.
The reason I suspect he didn’t confirm his findings with these experiments was because in the 1920s, we did not know there were different strains of C. perfringens. In the modern day we know that there are different C. perfringens strains, which have different pathogenicity. Not all strains cause gas gangrene, for example.
In modern times, we have learned that there are 5 main strains of Clostridium perfringens, and these strains produce different toxins, and therefore cause different health issues in humans.[2] Furthermore, not all isolates of C. perfringens strains DO produce toxins. Therefore, it is possible that there are different C. perfringens strains in salt rising bread starters and gangrenous wounds.
Therefore, even though Stuart Koser could make bread from a gangrenous wound sample, that is not necessarily the same C. perfringens strain in salt rising bread starters.

I will dive deeper into C. perfringens strains in Salt rising bread in the next few slides.

Slide 57 – Modern SRB experiments

The safety of salt-rising bread wasn’t assessed again until 2002 and again in 2008 at the University of Pittsburgh.

Slide 58 - A brief refresher on strains that cause disease in humans

Slide 59 - modern SRB experiment continued

In 2002 at the University of Pittsburgh, it was confirmed that C. perfringens grew in all SRB starters tested.
In addition, after baking salt rising bread, they were able to grow living C. perfringens from the baked bread, which tells us that some C. perfringens’ formed spores during the baking process. In these tests, there were significantly less C. perfringens in the baked bread than the starters, but C. perfringens was in the baked bread nonetheless.
So this implies that C. perfringens spores can survive the baking process. However, this experiment doesn’t tell us if the low number of surviving C. perfringens are harmful to consume.
Then as a follow up, more tests were done in 2008 at the University of Pittsburgh. A doctor and microbiologist, Bruce McClane, and his team examined the microbial community of dozens of salt-rising bread starters. In the salt rising bread starters his lab team found isolates of Clostridium perfringens strain A, which is the strain associated with gas gangrene and food poisoning.[2] However, the strain isolates they found in the starters could not produce the toxins necessary for gas gangrene or food poisoning.[24] So to be clear, these C. perfringens they found in the starters can’t cause disease.
Furthermore, most of the C. perfringens were inactivated when baking the bread to over 200°F (93°C) internal temperature, so the finished bread was deemed safe.[2]
So, this experiment indicates that the SRB starters they tested at the University of Pittsburgh were likely safe, but that does not mean all SRB starters are safe. Sometimes fermentation fails and people do not bake bread properly. Either way, it’s best to avoid feeding this bread to young and immunocompromised people, just in case it is harmful.

Slide 60 – More on Spores

As I mentioned, some C. perfringens survived after baking salt rising bread, and likely survived the baking process by first becoming spores. Although the bread was deemed safe for healthy people to eat, I still wanted to take a deeper dive into C. perfringens spore formation. So, let’s take a deeper dive into the sporulation process to see how C. perfringens does it.
List of info about spores… remember, spores help C. perfringens resist environmental stress, such as heat.

Before I get into the next photos I want to make something really clear. Everything I’ve researched has explained that C. perfringens cannot form toxins unless they become spores. They can then release the spores after they have a chance to germinate back into an active cell. Baking can trigger sporulation.

So I will walk you through a diagram of C. perfringens’s sporulation process.
First, we should note a normal cell life cycle where it is vegetative (living) and goes through binary fission to reproduce. This is the lefthand side of the figure, stages 0 and 1.[34]
Then, environmental stressors, such as lack of nutrients or unsuitable temperatures, cause the cell to begin form toxins and begin sporulation. I really want to stress that this is when the bacteria forms toxins, it forms toxins when it is under stress, which is why Salt rising bread isn’t 100% safe to eat.
Next, in stage 2 the cell divides within itself asymmetrically, forming two compartments that are divided by a cell wall. The larger compartment is the mother cell and the smaller compartment will become the pre-spore. Then in stage 3, the mother cell engulfs the pre-spore.
Stage 4 and 5 involves the mother cell beginning its work to protect the pre-spore.[31] The pre-spore is gradually developed and coated in protective layers such as proteins.[31] This kind of reminds me of when a mother puts so many layers of clothing on her child to prepare them for a winter storm that the child can barely walk until it gets to school. Except in this case, the child is extremely dangerous.
Once the spore is properly protected with all the necessary layers then in stages 6 and 7 the mother cell splits, or lyses. So essentially the mother cell dissolves, freeing her finished little spore baby into the environment.
What’s very important here is that lysis involves the release of toxins that were formed at the beginning of the sporulation process.[35]
That protected endospore can remain as a spore, but once environmental conditions are safe again this endospore can germinate into it’s own vegetative cell and begin reproducing again.[30]

So, if there’s anything you take away from this complicated figure, it should be that C. perfringens creates and releases toxins when it becomes a spore and then germinates.

Slide 61 Conclusion – What we don’t know

Although my plan for this presentation was to try to combine the history of salt rising bread with the microbiology of salt rising bread, and to see how the microbiology affects the bread making process.
I did make some guesses in this presentation. So I want to acknowledge that there’s still a lot we don’t know, and some of my suggestions may not turn out to be true in the future.
Most resources on SRB either focus on it’s history and tradition, or how it’s made with a dangerous bacterium. But there are not a lot of details about the microbiology and how it affects the bread. There were minimal sources on how C. perfringens actually interacts with the bread to change it’s structure relative to yeast bread. Obviously commercial yeast is well understood because it’s been an industrial process for over 100 years, but the salt rising bread method is not well understood. Even though a few studies have been done on the microbial community of select SRB starters, there’s a lot we don’t know about the microbial community or it’s activity within this bread.

So overall, although this presentation is incomplete by my standards, I hope this has given you lots of information about salt rising bread and it’s fascinating creation. Thank you for watching and listening to my extensive presentation.