What is Sourdough?
There is a common misconception that ‘sourdough’ refers specifically to a particular ‘flavor’ or bread, often a type of white bread that has a distinct sour taste profile.
But sourdough actually refers to any bread that has been made with a natural culture of wild yeasts and lactic acid bacteria (known as a sourdough starter) that is used to slowly ferment bread dough.
Most type of bread can be sourdough, whether it be crusty loaves, fluffy brioches or laminated pastries like croissants - breads that many wouldn’t associate with being sour at all. Some people are therefore of the opinion that the name ‘sourdough’ is actually a little inaccurate or misleading, and that sourdough should perhaps be re-named ‘naturally fermented bread’ to distinguish it from bread made using baker's yeast (aka commercial yeast/fast-acting yeast/dry yeast).
Sourdough bread in its purest form only contains three ingredients: Flour, Water, and Salt.
The sourdough starter that is used to leaven (i.e. make it ferment and rise) bread dough is made using a mixture of only flour and water and is produced by ‘harvesting’ wild yeast and bacteria that are naturally found in the environment (from the air and the surface of grains). This means that the particular species and strains of microorganisms found in a sourdough starters varies a great deal between regions and bakers, and each culture is believed to have its own unique characteristics. In fact, in 2013 a sourdough library was launched in Belgium where a collection of sourdough cultures from all over the world are being stored and studied (to find out more about the sourdough library click here). Through the studies over 700 strains of wild yeast and 1500 lactic acid species have been recorded so far.
Some of the strains of yeast and bacteria found in a sourdough cultures are unique to sourdough cultures and are not found anywhere else.
Bread made with a sourdough culture is sometimes referred to as ‘slow bread’ as one of the main differences between sourdough bread and bread made with commercial yeast is in the time it takes to make the bread.
Commercial yeast is made from a single strain of yeast isolated from a wild yeast culture for its ability to rapidly digest sugars and produce carbon dioxide (more information on this below).
Compared to bread made using commercial yeast, which may take as little as a couple of hours, the slow fermentation that happens in sourdough bread takes many more hours. The bread made at the Beach Cottage Bakery for instance is generally fermented for a minimum of 16 hours before it is baked.
This is Weck, the sourdough culture that ferments all the bread baked at the Beach Cottage Bakery (named after the Weck jar in which she* resides. I know, not very original).
Weck was born in May 2016 but has also been combined with a 40 year old starter given to me by another baker in LA.
(*She, because sourdough starters are also known as ‘mothers’).
A Very Brief History of Bread
Painted on the walls of 4000 year old Egyptian tombs are scenes from everyday life, including depictions of bread-making. There were even precisely drawn 'recipes' for bread-making, not to instruct the household cook, but to help the departed soul have some decent, freshly baked bread baked in the afterlife. (Read more about these fascinating paintings here).
It is thought that bread was discovered by accident about 6000 years ago in Egypt, when natural yeast found in the environment developed in a bowl of wheat porridge, fermented and rose when baked.
In time, people would have discovered that this ‘new food’ was more nourishing than the porridge it had been made from. Since this discovery people all over the world have been using ‘natural yeast’ (aka a sourdough culture) to make bread.
In the 1880s commercial yeast was introduced and quickly established itself as a standard ingredient in bread making.
Selected over countless generations and optimized for the role of putting gas into dough, the purified monoculture (single strain) of yeast, Saccharomyces cerevisiae, allowed bakers to produce bread in a fraction of the time sourdough cultures took, and also gave them a decisive gain in control due to its mechanical and predictable behavior, something that made it incredibly well suited for industrial bread production.
Although bread made using commercial yeast physically resembles bread made using a natural sourdough culture, the biochemical processes that lead to the final product are vastly different resulting in a significant difference in the chemical composition of the finished loaf. It is now increasingly believed that the slow fermentation that occurs in sourdough not only produces bread that is more nutritious, but that is also easier to digest, and that cutting out this crucial process through the use of commercial yeast may at least be partially responsible for the higher incidence of bread intolerance we are seeing in recent years (read more about this below).
Within the last century the speeding up of the bread making process for mass consumption has radically altered what we know as bread.
Whilst traditional sourdough bread contains three simple ingredients, flour, water, and salt, modern industrially produced bread often contains over 25 ingredients and additives. In order to produce a loaf in a minimum amount of time, a whole arsenal of additives becomes necessary. Among them, extra yeast, extra gluten, fat to improve softness, reducing agents to increase dough elasticity, soy flour to add volume, emulsifiers to produce bigger softer loaves and slow staling, and preservatives to extend shelf life.
Benefits of Sourdough Fermentation
Here is a list of the main benefits of bread made using sourdough fermentation. If you would like to find out more, each of these benefits will be explained in greater detail below.
Improved digestibility and access to nutrition
Believe it or not, grains did not evolve for us to eat them. Actually, that’s not quite accurate - they did not evolve for us to digest them. Being eaten is indeed beneficial for the plant as, if it passes through our system intact, the seed can be dispersed ad propagated far and wide. Grains therefore have evolved mechanisms that have been put in place to protect their precious nutrients, only making them available once the seed has been planted and has started germinating, upon which the seed provides enough energy and nutrition (including amino acids, oils and minerals) for growth until the plant is developed enough to start producing and absorbing its own energy and nutrients. What this means is that whilst grains (which are seeds of grasses) are little nutrient packets (or perhaps little plant starter kits), these nutrients are ‘guarded’ until the seeds receive signals indicating that it is time to release them.
The way the grains ‘protect’ their nutrients is through a substance called phytic acid.
Phytic acid serves as a plant’s main storage form of phosphorus. In addition, it binds to many minerals such as zinc, magnesium, calcium and iron. When phytic acid is bound to a mineral in the seed it is known as ‘phytate’. When a seed is ready to germinate, an enzyme called ‘phytase’ is activated, which breaks down phytates thereby causing them to release their bound nutrients.
Some animals, known as ruminants (e.g. cows, sheep, goats) have evolved to be able to digest grains and acquire nutrients from them by fermenting them in a specialized stomach prior to digestion, principally through microbial action which produces the enzyme phytase that breaks down the phytates.
Humans on the other hand do not have this ability and the consumption of grains can lead to problems with nutrient absorption and intolerances.
Phytic acid not only reduces the availability of nutrients by holding onto them and not letting go, but it also has the ability to bind to additional nutrients that it comes into contact with. For this reason, as well as inhibiting the absorption of nutrients found in grains, it is referred to as an ‘anti-nutrient’ as it also has the ability to inhibit the absorption of other minerals it comes into contact with within the digestive tract that may have come from other food sources.
So, if humans cannot eliminate phytates, how can we overcome the digestive problems caused by phytates? The secret is to trick the seed into ‘thinking’ it has been planted and is ready to germinate, and one way to achieve this is via fermentation using a sourdough culture.
Lactic acid fermentation in sourdough activates phytase which breaks down phytates, causing them to release the bound nutrients thereby making the grains much more digestible and nutritious.
In addition to neutralizing phytates, the acids produced by sourdough bacteria leads to the activation of numerous other enzymes. Complex carbohydrates are broken down from starches to more accessible sugars, and long protein chains are broken down into their amino acid building blocks. One of the proteins that is partially broken down is gluten. Everyone has heard of gluten, the protein found in several grains that provides structure to dough, allowing gases to be captured and the dough to expand in volume. Recent trends have demonized gluten and bread, claiming negative effects on or health.
However, some recent research has attributed the increase in gluten intolerance to the fact that modern breads no longer receive a lengthy fermentation and that without this, grain proteins such as gluten are left fully intact and hard to digest.
In addition, modern breads often contain additional gluten that has been added in order to make the dough more elastic thereby increasing its gas capturing capabilities. As sourdough fermentation partially breaks down gluten, it destroys at least some of the peptides thought to be responsible for gluten intolerances, which is why some people who are gluten-sensitive have been reported being able to digest sourdough without issue (please note gluten intolerance or gluten sensitivity is a very different issue to celiac disease which is a severe allergy to gluten).
Sourdough fermentation also helps to neutralize a substance called lectins.
Lectins are a type of protein found in many foods including grains and whilst some lectins can be beneficial, some act as anti-nutrients which can hinder the body’s absorption of nutrients as well as irritate the lining of the intestine.
The acids produced by the lactic-acid bacteria during fermentation play another important role. They actually kick start digestion even before the bread reaches your stomach by causing your mouth to water so that the enzymes in your saliva can begin to digest starches. It does not cause the dry sensation often experiences with industrially produced bread that makes you to reach for a glass of water.
Lower Glycemic Index
The glycemic index (GI) is a value assigned to foods (ranked on a scale of 1 to 100) based on how slowly or how quickly those foods cause increases in blood glucose levels.
Many modern bread products, especially white bread and highly processed bread, produce a high glycemic response (a quick spike in blood sugar) as the starches are quickly digested.
In sourdough, the fermentation process appears to lowers the GI of bread.
During fermentation the yeast and bacteria in the culture consume some of the starches and sugars in the flour, but it also appears that the acids produced during the fermentation process slows down the rate at which glucose enters the bloodstream. Further, a 2009 study from the University of Guelph suggested not only that naturally fermented bread had lower GI than whole-wheat bread made with commercial yeast, but also that the body’s glycemic response remained lower hours later.
Complex flavor development and robust texture
The metabolic by-products of various microbes is what is the key to the transformation of flour into bread.
Carbon dioxide produced by yeast and bacteria leaven (rise) the bread, while ethanol excreted by the yeasts contribute to aromas. The acids produced by the bacteria have a whole range of crucial effects. They contribute to flavor, strengthen the dough and as discussed earlier, increase the digestibility of grains. There is a fifth powerful flavor category the Japanese call umami (besides sweet, sour, salt and bitter) and natural fermentation is one way to bring out a broad range of umami flavors.
Lactobacilli bacteria outnumber yeasts in sourdough by as many as 100 to one, and it is the acid produced by these bacteria that produce aromatic compounds that infuses the bread with flavor, i.e. the flavors in bread are created by the microorganisms that ferment the flour, not the flour itself.
In contrast, bread made with commercial yeast contains a single strain of yeast and therefore the flavor profile that is developed is nowhere near as complex. To counter this, industrially produced bread contains a slew of additional ingredients to add flavor to the bread, most notably sugar.
Highly processed bread made with modern production methods have a very different texture to bread that has undergone traditional fermentation. Roll up a ball of processed bread and it sticks together into a tight ball and almost returns to its dough form. Sourdough bread on the other hand has a very robust structure. See for example this video demonstrating how a sourdough loaf behaves after having been squashed flat. Try the same thing with a loaf of Wonder Bread and it most certainly will not bounce back and retain its structure in the same manner. This structure is what gives sourdough bread it’s satisfyingly toothsome and chewy texture.
Production of natural preservatives
The lactobacilli bacteria in sourdough produces organic acids and antibiotic compounds that prevent competing microbes (non-sourdough microbes) from colonizing the culture.
This biochemical defense extends the shelf life of bread by acting as a natural preservative.
There is a relationship between a bread’s acidity and its keeping quality. As acidity increases so does the shelf life of the bread. Historically, rural Europeans baked bread only once every two to four weeks. The only breads that could keep that long naturally were bread with high acidity i.e. sourdough bread.
On Grains and Milling
None of the loaves made at the Beach Cottage Bakery are made using refined white flour alone. All loaves contain a proportion of stone-ground flour, milled from grains on the same day as the bread is made. To find out why this is important, please read the sections below:
Anatomy of a Grain
As you can see from the diagram above, even though the germ only forms about 2.5% of the kernel’s weight, it is the most nutrient rich part of the grain containing high levels of vitamins, minerals and fats. The germ is the embryonic heart of a grain.
When a grain germinates, it is from the germ that the rudimentary roots and shoots of the new plant emerge.
Part of what makes the germ so nutritious - its unsaturated omega-3 fats, also makes it unstable, and once a grain has been milled into flour it has a relatively short shelf life largely due to these fats turning rancid. Whilst sifting stone-ground flour removes the bran (the outer layer of the grain) it does not remove the perishable germ. Therefore, flour needs to be milled frequently and locally, which is why historically all towns used to have their own mill.
The advent of ‘roller-milling’ (as opposed to stone-milling) in the middle of the 19th century allowed white flour to be made whiter, cheaper and more stable.
This is because the process allowed the germ as well as the bran layer to be sheared off of the grain, leaving just the endosperm to be milled into a fine flour. Without the troublesome germ the shelf life of flour can be extended indefinitely.
Even when producing whole-wheat flour, when roller-milling is used the germ and bran is always removed at the beginning of the milling process. This is because the oils cause issues by gumming up the milling machinery. Most commercial flour is therefore white flour to which the bran and germ has been added back. However there have been claims that some mills only add part of the bran back and not the troublesome germ. If this is true then there really isn’t anything “whole” about this whole-wheat as the nutritional profile of the flour has been weakened.
Roller-milling also removes the innermost layer of the bran known as the aleurone layer which is nutrient rich and high in antioxidants. In stone-milled flour the aleurone layer becomes integrated with the endosperm and is therefore not separated.
The moment that the seed is opened up (by milling or otherwise) is the moment of its greatest potential. As soon as it is milled it begins to oxidize, losing energy that could be nourishing. It is also the moment of maximum flavor before it begins to fade.
Freshly milled whole-grain has a sweet fragrance and in fact the word ‘flour’ is a specific use of the word ‘flower’ in the sense that flour is the “finest portion of ground grain” in the same way that a flower is the finest part of a plant. It was spelled flower until the 1930s when flour became the accepted form to end confusion.
Bread made purely with whole-grain flours whilst highly nutritious can be tougher due to the coarse fiber in the heavy bran. In addition, the bran in the flour acts as tiny little shards with cut through gluten networks making it difficult to trap air, which results in denser loaves than those made with refined flours.
At the Beach Cottage Bakery I strive to strike a middle-ground. All loaves are made with a combination of freshly stone-ground whole-grain flour at its maximum flavor and nutritional potential and refined flours to achieve loaves with a more open and chewy texture that is widely appealing.
Types of Grains: Why wheat?
The preeminence of wheat as food stuff is centuries old. More than eighteen thousand years ago in what is now Iraq and Syria, wild grains such as emmer and einkorn (species of wheat) were being harvested by humans.
Now wheat is grown on more land area than any other food crop and the world trade in wheat is greater than for all other crops combined.
Grains, commonly referred to as ‘cereals’ or ‘cereal grains’, are the edible seeds of specific grasses and there are many types of grains we eat other than wheat such as barley, buckwheat, oats, spelt, and rice (see below for a more extensive list). So what is it that makes wheat so special?
Wheat has come to dominate the grains we eat because it contains a large amount of gluten, the elastic protein that enables bakers to create satisfyingly risen breads.
It is almost impossible to make an acceptably risen loaf without at least some wheat mixed in. However, when it comes to nutritional content there is no such thing as the “healthiest” grain - some are stronger in one nutrient and others in different nutrients (for more information on different grains and their nutritional content please visit the Whole Grains Council.
Just as the nutritional content varies between different types of grains, so does their flavor and texture. I believe that it is an immense shame to limit the grains contained in bread to a single species of grain and loaves made at the Beach Cottage Bakery often contain one or more of the following grains in addition to wheat.
For more information on these different grains and a few interesting facts about each one of them please see the Whole Grains A to Z from the Whole Grains Council.
Gluten free flours (such as buckwheat, millet and rice) are difficult to make bread with for the aforementioned reason: gluten is necessary to build dough structure that allows bakers to trap gases produced during fermentation. However, gluten free flours can be added in small proportions to wheat without greatly impacting the final structure of the loaf.
Regardless of their gluten content, all grains benefit from sourdough fermentation to improve digestibility and make the nutrients more accessible.