Gluten-Free Sourdough: the Science Behind What Happens in Your Jar

So you want to take a leap of faith, and create a gluten-free sourdough starter from scratch? I know it's intimidating... and I'm talking from experience since it took me an entire year of thinking about sourdough before I dove in. But I'm here to tell you that it is not scary at all! Even more than that, the science of gluten-free sourdough is on our side. What I mean by that is the balance of wild yeast and good bacteria we want in a sourdough starter "wants" to naturally happen; in science talk, it's the natural equilibrium. With nature on your side and a few commonsense tricks, you can have a healthy gluten-free sourdough starter in no time! Well... in about 10 days.

This post is going to outline the scientific principles behind creating a gluten-free sourdough starter. It's meant as a primer to boost your confidence and understanding, before you jump into the recipe for a gluten-free sourdough starter, and later gluten-free sourdough bread.

What is sourdough?

Sourdough is essentially a microbial culture of wild yeast and bacteria, and their house is a mixture of flour and water in a glass jar. Where do they come from? They're all around us! On our hands, in the air, on our countertops, in the bag of flour itself... A sourdough starter is simply a mixture of gluten-free flour, wild yeast/bacteria, and water, where cellular activity can proliferate.

There are many different organisms capable of thriving in a sourdough starter. In fact, the diversity is such that a sourdough bread from one household to another will have a different taste, because different microbes produce unique chemicals. That's super cool!! There's several labs and studies that analyze all those compounds and diversity, and even a public project at North Carolina State University, where you can characterize your sourdough starter, for science.

How does a sourdough starter establish itself?

Let's dive into the science of gluten-free sourdough. Microbes eat, reproduce and die. The starch in gluten-free flour can be broken down by the microbes' enzymes into simple monosaccharides, and then used for cellular activity.

Aerobic versus anaerobic respiration

I talked about cellular activity, but what does that mean? Well, it's all the chemical processes that go on inside a living cell. Some of those processes happen aerobically, meaning they require oxygen, while others happen anaerobically, in the absence of oxygen. This is an important differentiation to make when diving into sourdough, as it will help us make the right decisions for covering our starter.

According to Explore Yeast, wild yeast functions under both aerobic and anaerobic metabolic pathways.

And so, the byproducts of cellular activity in a healthy sourdough starter, whether aerobic or anaerobic, are CO₂, water, energy, ethanol and lactic acid. The carbon dioxide is what makes bread rise, provided our gluten-free formulation contains hydrocolloids to trap CO₂. The ethanol can give that strong nail polish remover smell that tells us our yeast is "hungry"! Basically, we can assume that if we smell the alcohol, a lot of the starch has been broken down and eaten, and we should give our yeast more starch to eat.

What is a "good" bacteria?

So I've talked about "good" bacteria, and the reason we call it good is because it is producing acid. An acidic environment is not conducive to life, since hydronium ions can interfere with cellular function. The kicker here is that the wild yeast we want to cultivate is resistant to acidic environments! So the "good" bacteria is creating a microbiome that decreases resource competition for wild yeast to thrive! Furthermore, the acidic environment prevents harmful bacteria from growing, which makes sourdough safe for our consumption and enjoyment.

The yeast and bacteria in a sourdough starter are in a symbiotic relationship, meaning they both help each other out. According to an article by Colorado State University, yeast helps bacteria break down proteins into absorbable peptides, while the bacteria releases excess glucose and converts the ethanol into acetic acids, thus lowering the pH of the starter. Some strains of the lactobacillus bacteria even produce chemical compounds that act as mold-killers.

And that's exactly what establishing our gluten-free sourdough starter means: lowering the pH and creating an environment that is hostile to all other microbes other than yeast and "good" bacteria. This takes (on average), around 10 days to accomplish.

What is pH?

pH stands for Power of Hydrogen, and is a scale that measures the concentration of hydronium ions in a solution. The scale goes from 0 to 14, where 7 is the pH of water and is considered neutral. A low pH means a solution is acidic, and a high pH means it is basic. Examples of alkaline (basic) foods are kale, avocadoes, and beets; examples of acidic foods are vinegar, buttermilk and pickles.

For our gluten-free sourdough starter to be ready, we are looking for a pH of around 4. Remember, a neutral pH is 7. The pH scale is logarithmic, so it does not mean that sourdough is 3 times (7-4=3) more acidic than water; 3 represents the magnitude. In other words, that's the number of zeros in front of a 1. So an established sourdough starter is actually 1,000 times more acidic than water. And it takes some time to get there!

Creating a starter day by day

In my recipe for creating a gluten-free sourdough starter, you will see that I have day by day instructions for YOU to follow. In this paragraph here, I'll explore the science of gluten-free sourdough. We will see what happens to the microbes in your starter, as you go through the motions. Please note that this is an oversimplified model, but it will still give us a great idea of what's happening on a microscale.

The takeaway from the above infographic is that as yeast and "good" bacteria eat the starch in our gluten-free flour, they are slowly creating byproducts that are detrimental to their competition. Therefore, after about 10 days on average, our gluten-free starter contains only yeast and acid-producing bacteria, which means it is safe to use.

Day-by-day

• Day 1: the gluten-free starter contains yeast, good and bad bacteria, all found in the air, our hands, and the gluten-free flour itself.
• Day 2: microbes proliferate. As the good bacteria eats the starch in the gluten-free flour, it is producing lactic and acetic acids. The higher hydronium ion concentration is already making it difficult for the bad bacteria to thrive.
• Day 3: we discard a big portion of the starter and decrease the absolute population of bad bacteria. Though the ratio of good:bad bacteria is not affected by discarding, keep in mind that the pH of the starter is still dropping.
• Day 4: the acidic environment is unfavorable to the bad bacteria.
• Day 5: a colony of only yeast and good bacteria establishes itself.
• Day 7: the pH is now low enough that the starter is considered safe to use.

A note on discarding: we discard first and foremost because we want to keep our starter at a small manageable size. Feeding a 1:1:1 ratio daily would mean 30 grams of flour on day 1, 90 grams of flour on day 2, 270 grams of flour on day 3, and so on! It would be expensive, and we would run out of jar space. At the beginning, throw away your discard full of bad microbes! Once the starter is healthy and established, we can use the discard to bake!

We have to feed our gluten-free starter with mineral-containing water (drinking water) and fresh gluten-free flours. But as you can see, the natural equilibrium of the starter tends towards an environment that is acidic, where wild yeast and lactobacillus bacteria can thrive. Stop being scared, nature is on your side!

Caring for an established starter

Once your gluten-free sourdough starter is established (yay!) we are in maintenance mode. I keep my starter, Ben Swollo, in the fridge and maintenance feed him weekly. Sometimes more, if I'm baking.

Before I dug into the science of gluten-free sourdough starters, I knew to keep my glass jar covered with a cloth lid on the counter, or with a tight-fitting lid in the fridge. And now, based on what we have learnt about anaerobic and aerobic metabolic pathways, we can understand those storage recommendations.

What's the difference between a gluten-free and regular sourdough starter?

Beyond the obvious that a different flour is used, there are a few key differences that you can expect to see from your gluten-free sourdough starter.

The rise

Gluten has a very specific role in baking: it traps CO₂ in a three-dimensional network that allows bread to expand. In a regular starter, as bacteria and yeast go through cellular activities, the gases get trapped, and you can observe BIG rises in your jar.

However, in a gluten-free sourdough starter, there is no gluten to trap gases. Most of the CO₂ produced during fermentation is going to escape the starter. I know it can be disappointing as a baker because we don't SEE a huge rise which is a visual indicator that we are on the right path. This is what I see in my kitchen after fermenting for 24 hours, maybe a 50% rise.

Along with the visual cue of a small rise, the best indicator of your gluten-free starter's health is its smell. It should be yeasty, you may even detect a vinegar-like odor (acids). Those are great indicators of the cellular activities of the wild yeast and good bacteria. The above pictured starter smelled like red wine (ethanol)!

The consistency

The next big difference between regular and gluten-free starter is consistency. Take a look at my Gluten-Free Flour Guide, and you'll see flours classified by their capacity to absorb water. We typically feed a sourdough starter at a 1:1:1 ratio, which for example could mean 30 grams of starter, 30 grams of flour and 30 grams of water. Wheat absorbs water differently than brown rice, which in turn is different than sorghum or buckwheat. And so when making a gluten-free starter, we have to keep in mind that consistency is going to be different based on what flour we use! Furthermore, superfine flours absorb more water.

I have had a lot of discussions about starter consistency. Some gluten-free starters are runny, some gluten-free starters are thick. A runny starter may increase the amount of available oxygen pockets and so the wild yeast may stay in aerobic mode longer. In a thick starter, ethanol may be produced at a faster rate. You can watch this quick clip to see my sorghum starter's consistency.

My key takeaway is to be consistent in my feeding ratios. I have had great success with my thick superfine sorghum starter that absorbs a lot of water, fed at a 1:1:1 ratio +5% water. The reason to stay very close to a 1:1:1 ratio is because when we actually bake a bread, virtually all recipes are written taking into account the 1:1:1 hydration of the starter. Also, another important factor to consider for consistency is that as yeast and bacteria go through their cellular activities, water, ethanol and lactic/acetic acids are byproducts, and they are all liquids at room temperature. And so as time passes and starch is broken down, a thick starter will naturally get thinner.

How do I control the taste of my sourdough?

If our gluten-free sourdough starter favors the yeast, we will have milder yeasty flavors. However, if our gluten-free sourdough starter favors the acid-producing bacteria, our bread will be more sour. Well, let's take a look at the conditions that favor these two scenarios! This information is summarized from this article.

Conclusion

That was a lot of information you guys! Bookmark this page and come back to it once the information has started to sink in! The bottom line is: the science of gluten-free sourdough is on your side. This healthy symbiosis between the wild yeast and the acid-producing bacteria naturally wants to happen.

When you're ready, head on over to the instructions to create a gluten-free starter, where we will apply what we've learned here.

If you have any questions, comments, knowledge to add, please leave a comment!