Understanding your sourdough report: A guide to reading and interpreting figures

How to understand figures and interprete results

Keep scrolling to explore the individual figures and learn how to efficiently interpret the data presented in the Citizen Science report. Each section will guide you step by step, helping you understand the key insights from your sourdough’s microbial composition and fermentation characteristics!

Map with the closest relatives of your sourdough:

Each dot or star on the map represents one sourdough. Your sourdough, or in our example right here Luftibus, is shown as an orange star. When we study the microbial composition of sourdoughs, we can group them into family trees based on how similar their microbial communities are. Think of it like a family reunion some sourdoughs are closely related (closer relatives including direct family members, like siblings or even twins), while others are more distant relatives. To build this sourdough family tree, we use a method called hierarchical clustering. It’s basically sorting sourdoughs by their microbial DNA, placing the most similar ones close together and the more different ones farther apart. For those curious about the details, we use a Bray-Curtis metric to measure these microbial similarities and differences.

Now, back to your sourdough, or Luftibus! The yellow stars on the map represent sourdoughs that are most similar to Luftibus in terms of their microbial composition. If you see a yellow star close to your orange star, it means that these sourdoughs have very similar microbial communities and were likely created in a nearby location, or even descendants of your sourdough (?!). If you don’t see any yellow stars, that means all of your most similar sourdoughs are directly overlapping with your orange star. In this case, they likely come from very close to your location, perhaps even from the same town or region! You might also notice yellow stars far away from your own sourdough’s location on the map. This could mean that your sourdough has some long-distance relatives! There are two possible explanations for this:

• Migration: Maybe a sourdough similar to yours traveled across Europe, perhaps someone moved with it, shared it with a friend, or passed it down through generations.
• Independent Creation: It’s also possible that another sourdough enthusiast, using similar ingredients and fermentation methods, naturally created a sourdough with a microbial community very similar to yours - just by coincidence!

Spider plot with fermentation preferences

How to read the spider plot
The spider plot compares three different profiles:

• All sourdoughs (green): The average profile across all sourdoughs collected in this study.
• Same flour type (brown): The average profile of sourdoughs that use the same flour type as yours. Since here in our example Luftibus is a non-wholemeal rye sourdough, this brown line represents the average of all non-wholemeal rye sourdoughs.
• Your sourdough (orange): Your individual sourdough profile, shown in orange. You can find these colour-coded labels in the legend below the spider plot.

What do the spider axes mean?
Each axis in the spider plot represents a different variable, with its range of values shown. If a unit is given in brackets (e.g., °C, g/cm³, h), it means the variable has a specific measurement unit. If no unit is given, the variable is just a number (for example the pH). Example interpretation: Spider axes dough yield vs. bread density Let’s take a closer look at two variables to understand how to read this plot:

1. Dough Yield (Example: Luftibus at 200)

• In this example, all three profiles (green, brown, and orange) overlap perfectly at Dough Yield = 200.
• This means that on average, most citizens maintain their sourdoughs at Dough Yield 200, regardless of the flour type.
• This variable shows very little variation across sourdoughs (1).

2. @Home Measured Bread Density (Example: Luftibus at 0.56 g/cm³)

• Here, the three profiles do not overlap. Instead, they cross the axis at different values:
• All sourdoughs (green): ~0.425 g/cm³
• Rye sourdoughs (brown): ~0.47 g/cm³
• Luftibus (orange): ~0.56 g/cm³ (even higher than the rye average)
• This shows that this variable has higher variation across sourdoughs (2).
• Since higher density means a more compact and less fluffy bread, this suggests that Luftibus produces a denser bread than most other rye sourdoughs.
• A possible reason? Lower yeast abundance, leading to less leavening activity. Or some bacteria that interfer with leavening activity of yeast.

What can you learn from this spider plot?
With this plot, you can compare your fermentation preferences with others and see how they relate to sourdough and bread characteristics.

• Variables related to fermentation practices (like feeding temperature, storage temperature, feeding time, dough yield, dough size, and backslopping frequency) are highlighted in blue.
• Variables related to bread outcomes (like sourdough and bread pH values, as well as bread density) are highlighted in pink. This allows you to see if your fermentation habits increase or decrease key factors like sourdough acidity, bread pH, or bread density, compared to both all sourdoughs and sourdoughs with the same flour type as yours.

Bar charts for acidity and age

How to read the pH and age distribution bars
This figure contains two horizontal bars:

• Upper bar: Shows the distribution of pH values across all collected sourdoughs.
• Lower bar: Displays the age distribution of all collected sourdoughs.

Example: Understanding the pH Distribution The upper bar represents the full range of pH values measured in the collected sourdoughs, running from 3.3 (left) to 5.25 (right).

• The colour intensity in the bar indicates how many sourdoughs fall within each pH range.
• Darker areas mean more sourdoughs had that pH, while lighter areas mean fewer sourdoughs.

Example interpretation: Sourdough pH

1. The dark grey section between pH 3.5 and 3.6 (1) indicates a high number of sourdoughs in this range.
2. Checking the colour legend (‘Number of sourdoughs per range’) (2), dark grey represents around 100 sourdoughs.
3. The black section from pH 3.6 to 3.8 (3) spans two predefined 0.1-step pH areas. Referring to the color legend (2), black represents about 180 sourdoughs per 0.1 pH step, meaning that around 360 sourdoughs had a pH between 3.6 and 3.8.
4. The example sourdough Luftibus had a pH of 3.9, marked in orange (4). Since 3.9 is at the upper edge of the dark grey area, it means that Luftibus has a higher pH than most other sourdoughs, making it less acidic compared to all others.

What can you learn from those pH and age bar charts?
This visualisation helps you understand where your sourdough stands in terms of acidity and age compared to all other collected sourdoughs.

• If your sourdough’s pH (or age) is in a darker area, your sourdough is similar to many others.
• If your sourdough’s pH is in a lighter area, your sourdough is less common in acidity.

Bar charts for yeast and bacterial cell abundance

How to read the yeast and bacteria abundance bars
The two horizontal bars below represent:

• Top bar: Yeast cell abundance (cells per gram of sourdough).
• Bottom bar: Bacteria cell abundance (cells per gram of sourdough). As seen in Fig. 1C, the darker the area, the more sourdoughs fall within that cell count range. You can estimate the total number of sourdoughs in each range by referring to the color bar ‘Number of sourdoughs per range’.

What do we learn from the microbial abundance charts?

• Most sourdoughs contain 3-10 million (mio.) yeast cells per gram of sourdough (1).
• Most sourdoughs contain 1-3 billion (bio.) bacteria cells per gram of sourdough (2). This means that, on average, sourdoughs contain about 300 times more bacteria than yeast.

How does your sourdough compare?
Our example sourdough, Luftibus, has:

• 275.46 million yeast cells/g, meaning it has more yeast cells than the average sourdough.
• 870.76 million bacteria cells/g, meaning it has fewer bacteria cells than the average sourdough. Since Luftibus has only ~3x as many bacteria as yeast, compared to the 300x ratio in most sourdoughs, its microbial balance is quite different from the typical sourdough.

Microbial fingerprints of sourdoughs

In the Bacterial Fingerprint and Yeast Fingerprint sections, you will see:

• The average bacterial and yeast composition for your sourdough class (a group of sourdoughs with similar microbial profiles).
• The exact bacterial and yeast composition of your own sourdough, allowing for direct comparison to other sourdoughs.

What is a Sourdough Class? Just like in Fig. 1A, we used the same family tree of sourdoughs, based on their microbial fingerprint (i.e., their bacterial and yeast compositions combined). In any family tree (see the following graphic), some members are closely related (forming "subtrees"), while others are more distant relatives. When building this microbial family tree, we didn’t just identify each sourdough’s closest "relatives" — we also grouped sourdoughs into five distinct clusters, or sourdough classes. Each class represents a group of sourdoughs that share similar microbial communities.

What does this mean for your sourdough? Sourdoughs in the same class share similar microbial communities (both bacteria and yeast). This allows us to calculate the average microbial composition for each class, which we display as a signature profile for both bacteria and yeast per class. By comparing your own sourdough's fingerprint to your class average, you can see how unique or typical your sourdough’s microbiome is!

Why are bacteria and yeast analysed separately? Bacteria and yeast are fundamentally different microorganisms, both in size, genetics, and function within sourdough fermentation.

1. Biological differences

• Bacteria are prokaryotes - they are smaller and have only one single chromosome and belong to the bacterial kingdom, and they are even their own bacterial domain.
• Yeast are eukaryotes, they have multiple chromosomes and belong to the fungi kingdom - just like mushrooms, plants, animals, and even humans! Because of these genetic differences, we need different methods to identify bacteria and yeast, which is why they are analysed independently.

2. Different roles in sourdough fermentation

• Bacteria: Their main role is acidification, meaning they lower the pH of the sourdough. This prevents spoilage from harmful bacteria and gives sourdough its distinct sour flavours.
• Yeast: Their key function is leavening - they produce gases that make the dough rise, creating the characteristic fluffiness of sourdough bread. Yeast also contribute to unique aromas and flavours.

3. Why does this matter? Since bacteria and yeast serve different functions, it makes sense to study them separately when investigating sourdough microbial communities (and any other microbiomes in other food fermentations, in nature or also in our gut microbiome). However, we can also look at how bacterial and yeast species interact within the same sourdough class to discover:

• Which bacteria and yeast tend to co-exist?
• Which species rarely appear together? Understanding these microbial relationships helps us learn more about how fermentation works and what makes each sourdough unique!

Bacterial composition bar plot

How to read the compositional bar plot
Let’s go through the entire graph together! This type of graph is called a compositional bar plot, and it helps visualise the different bacterial species found in various sourdough classes.

Step 1: Understanding the axes of a compositional bar plot
X-axis (horizontal axis):

• This shows the five different sourdough classes (labeled 1 to 5).
• It also includes your own sourdough with its unique name and class. In this example, Luftibus belongs to class 3 (1). Y-axis (vertical axis):
• This represents the proportion (%) of each bacterial species in a given class (2).

Step 2: Interpreting the bars in a compositional bar plot

• Each bar represents a sourdough class and is divided into stacked color-coded segments (3).
• Each colour corresponds to a bacterial species, which can be identified in the legend under “Most Prevalent Bacteria in All Sourdoughs” (4).
• Larger segments mean that a species is more abundant in that class (dominant).
• Smaller segments mean the species is less common (subdominant).

Let’s analyse Class 1 as an example:

• The bar is divided into five color-coded segments, each representing a bacterial species (3).
• The species most commonly found in Class 1 are:
  Blue: Lactobacillus brevis → ~4% Light blue: Lactobacillus hammesii → ~2% Green: Lactobacillus mindensis → ~2% Lighter green: Lactobacillus parabuchneri → ~1% Very light green: Lactobacillus plantarum → ~1% Yellow: Lactobacillus sanfranciscensis → ~88% (dominant species!) Purple: Pediococcus pentosaceus → ~2%
  This means Class 1 is mostly dominated by L. sanfranciscensis, while the other six species are commonly less abundant (subdominant species). This same approach can be applied to all other classes, as well as to your own sourdough.

Step 3: How does your sourdough compare?
Now, let’s look at the individual bar of our example sourdough Luftibus:

• It consists of 2 bacterial species Pediococcus pentosaceus (99.59%) and Lactobacillus sanfranciscensis (0.40%) (5).
• Unlike its class, class 3 (which has multiple species with two dominant and 3 supporting species), Luftibus is completely dominated by a single species and hosts one supporting species.

Step 4: Additional information below the compositional bar plot
Below the figure, you’ll find a detailed description of the sourdough class that your sourdough belongs to.

• For Luftibus, which is in Class 3, this section explains the average microbial composition in that class.
• In this example, Class 3 typically has five bacterial species: 2 dominant species and 3 subdominant (supporting) species

Along with the bar plot, you’ll also see a detailed list of the bacteria in your own sourdough (6). If this list contains more species than those shown in the bar for your sourdough (5), it means that your sourdough contains rare bacterial species that are not commonly found in other sourdoughs.

• Since the plot only shows the most prevalent bacteria in all sourdoughs, unique bacteria might not appear in the graph but will be listed in your individual results.
• 💡Takeaway: The bar plot helps you compare your sourdough’s bacterial fingerprint to others, while the list provides a more detailed and personalized breakdown of your sourdough’s unique bacteria!

Yeast composition bar plot

This figure can be read and interpreted in the same way as the Bacterial Fingerprint figure - except that it represents yeast species instead of bacteria. In the example of Luftibus, the rightmost color bar represents its yeast composition:

• A very small fragment at the bottom corresponds to Kazachstania servazzii.
• The large brownish bar represents Saccharomyces cerevisiae. From the species listing below the plot, we see that:
• K. servazzii has a relative abundance of ~1%, making it subdominant.
• S. cerevisiae makes up ~99%, meaning it is highly dominant in Luftibus.

Do you have more questions about your sourgdough report?

Then meet Dough-Pro!
Dough-Pro is your personalised sourdough assistant – a friendly AI that can answer all of the above and more. From science to sourness, and fluffiness to fermentation facts, Dough-Pro has your dough covered.

👉 Get to know Dough-Pro
👉 Chat with Dough-Pro

Please note: Dough-Pro runs on OpenAI technology, so you may be asked to log in or create an OpenAI account when chatting for the first time. After that, you’re all set to talk sourdough (or anything fermentation related) as often as you like!

The authorAnnina Meyer

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