In The Sourdough School: The Ground-Breaking Guide to Making Gut-Friendly Bread by Vanessa Kimble, readers will learn to master the art of sourdough from the expert herself. Kimble uses the teachings from her renowned Sourdough School in a brilliant compilation of easy-to-follow instructions and stunning photography. Readers of all experience levels can try their hand at the timeless craft of artisan baking with this indispensable guide. The following excerpt is from Chapter 5, "The Foundation for Your Loaf."
Before you begin, you need a starter, and to understand how to create and look after it. You can make your own by capturing the wild yeasts and bacteria already present on the grains that your flour is milled from. This is fun, and will give you a huge sense of satisfaction, but it takes a little time. Depending on the ambient temperature of your room, and the microbial activity of the flour you are using, it can take from three days to two weeks, so if you are full of enthusiasm about starting baking, I suggest that you begin by making a loaf with a thriving starter that is already producing great loaves for someone else. If you don't have a baking friend who will give you a small amount of their starter, you can buy an established one from one of the online resources. Scientific studies indicate that an established starter is stable, active, and resilient, and in your first attempts at making sourdough bread, it will guarantee a better loaf, which is more likely to keep you baking.
Sourdough is a symbiotic microbial ecosystem made up of wild yeasts and lactic acid bacteria that have colonized the mixture of flour and water. The behavior and the characteristics of your starter depend on the type of yeast and lactic acid bacteria, which in turn depend on the temperature at which your starter is refreshed, the kind of flour used to maintain it, and the resident bacteria in the environment that it is kept in.
Do I need to understand the microbes to make great sourdough?
No — people made bread for thousands of years before we even invented microscopes or knew of their existence — though a basic knowledge will help you better understand how to change the flavor of your bread. At the School, we have students from all over the world who want to understand how they can use fermentation to experiment with flavor, and make more nutritious bread. Controlling the levels of acid in the dough influences the flavor and the level of sourness, which in turn affects the gluten structure, texture, and crumb of the bread. So it is very useful to understand where the acids come from, and what they do.
Where do the bacteria come from?
The flour that you use to refresh your starter is a major influence on the kind of bacteria that colonize your starter.
What other factors affect the starter?
The soil that your flour is grown in can affect the kind of microbes you get colonizing your starter, as can the environment in which you keep your starter, and the temperature at which you refresh it. The farming practices used to grow the grain (usually wheat) also affect the microbial composition.
What is in the starter?
There are two kinds of microorganisms that cause sourdough to ferment: yeasts and lactic acid bacteria (LAB). These have a mutually beneficial symbiotic relationship, sharing the available nutrients from the flour. Mostly, rather than compete for food, they cooperatively protect their ecosystem from other uninvited bacteria.
There are about 23 known species of yeast, but the most common ones are Saccharomyces cerevisae and Kazachstania. The yeasts are tiny, oval-shaped one-celled fungi, though are much bigger than the LAB. When they have access to oxygen, aerobic fermentation produces carbon dioxide gas, which makes your bread rise.
Sourdough bacteria are predominantly lactobacilli and are also found in other fermented foods, such as kefir and sauerkraut. These bacteria are responsible for producing the unique by-products that enhance the flavors and textures of sourdough, in particular, producing the organic acids that change the pH of the dough.
How does sourdough ferment?
When the yeasts have access to oxygen, aerobic fermentation causes them to grow more cells. Once the oxygen is then used up, they change to anaerobic fermentation, which is much like fermenting beer; the yeasts make both alcohol and carbon dioxide gas (CO2) using up the simple sugars that the enzymes have broken down. The bubbles that you see in the bread dough are the released gas, and are what make your bread rise.
At that same time the LAB which are responsible for producing the unique flavors and textures of sourdough, produce organic acids that change the pH of the dough, which is key to the increased nutritional value and digestibility of sourdough.
Are there different kinds of lactic acid bacteria?
Yes. There are many species that produce different flavors and textures, but LAB are categorized based on their by-products. The following terms might sound technical, but once you know that homofermentative LAB is the bacteria found in yogurt, it becomes more understandable.
Sour, Vinegary Flavors
- Obligate Heterofermentative: Ferments glucose and produces ethanol and both acetic acid and lactic acid, as well as carbon dioxide (CO2) as by-products, which produces a more sour and vinegar-flavored bread.
- Facultative Heterofermentative: Produces mainly lactic acid, but in some cases, it can also produce acetic and lactic acids.
- Obligate Homofermentative: Ferments glucose and only produces lactic acid as the primary by-product, which is milky, and produces a sweeter, more yogurt-flavored sourdough.
How do the bacteria Affect the bread?
The bacteria produce organic acids that acidify the dough. This acidity is one of the main reasons sourdough is more nutritious and more digestible. Their other job is to produce exopolysaccharides, a kind of sugar slime that the bacteria like to live in. These exopolysaccharides have two main benefits. Firstly, they provide a structure and change to the mouthfeel of the bread — there are some specific bacteria, leuconostoc, for example, which have been identified for producing dextran, resulting in the voluptuous, soft, sweet mouthfeel of classic panettone. Secondly, exopolysaccharides make great food for our gut microbes, even when baked.
What is a typical sourdough ratio?
In January 2017, the School's French white sourdough starter, derived from the original French starter from the bakery I grew up baking in, was analyzed by the Puratos Sourdough Library in Belgium. This analysis revealed that it contained one dominant yeast and several kinds of LAB, which is typical of the makeup of all starters.
We have four starters at the school, each one producing sourdough with different flavor profiles:
Sweet yogurt-like flavors.
- Yeast = Saccharomyces Cerevisiae
- Lactobacillus kimchii
- Lactobacillus sanfrenciscensis
- Lactobacillus acidifarinae
Lactic, both tangy, milky, and fruity.
- Lactobacillus plantarum (43 percent)
- Lactobacillus sanfranciscensis (38 percent)
- L. fermentum (16 percent)
- Fructoe pseudoficulneus (12 percent)
- Acetobacter pasteurianus (8 percent)
Sour and deeper, darker treacle and complex flavors.
- Lactobacillus sanfranciscensis (32 percent)
- Lb. acidophilus (22 percent)
- Lb. pentosus (17 percent)
- Lb. pontis (8 percent)
Sour and sweet malt and beer flavors.
- Lactobacillus acidifarinae (48 percent)
- Lactobacillus kimchii (37 percent
- Lactobacillus sanfranciscensis (21 percent)
- Lb. pentosus (13 percent)
- Lactobacilli brevis (10 percent)
More from The Sourdough School:
- Why You Should Sprout Your Grains and Seeds
- Malting Grain to Boost Your Sourdough
- Russian Rye Bread Using Excess Sourdough Starter
- Herb Butter with Wild Garlic Recipe
- Chocolate and Roasted Hazelnut Bread
Excerpted from The Sourdough School, by Vanessa Kimble © 2018. Published by Kyle Books, and photographs © Nassima Rothacker. No images may be used, in print or electronically, without written consent from the publisher.