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What is Sourdough bread?

A tray full of different sourdough breads

We hear a lot about sourdough of late. There’s so much confusion about what sourdough bread actually is (or isn’t), so we thought it time to clarify our position and hopefully give you (our readers) a better understanding of what it all means.

Being a pastry chef, I’m interested in all kinds of bread, from quick “no yeast” all the way through to beautiful sourdough.

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At Bec’s Table, we believe that sourdough bread is defined by the processes (such as proving and the lack of kneading) and the microorganisms used to develop taste, smell, and texture (i.e. the rise and softening).  In effect, we define sourdough bread as the type of bread-making before industrialization and the subsequent cultivation and use of bakers yeast.

Sourdough round loaf.
Sourdough round loaf

Be assured that we have nothing against bakers yeast. It’s a very effective product, and we routinely make bread with it.  However, so much of our food in western society is produced by others, whose aims are efficiency and profitability.  Whilst this has decreased the price we pay for food (which is good), we are a little concerned that we have lost touch with what food is, where it comes from, and possibly the long term implications for our health.

Our definitions for bread are;

Modern bread:

Made using bakers yeast, and with processes and methods aimed at mass production, with the cost being a significant driver.

Sourdough bread:

It’s made using a mix of yeast and bacteria, without the addition of bakers yeast, with processing times, and method consistent with the creation of food for its taste and nutrition, as opposed to the lowest cost of manufacture.

Faux sourdough:

We have no issue with making bread with the addition of bakers yeast to reduce proving time (or any of a number of non-traditional shortcuts or tweaks), but we prefer to call this a Faux sourdough.

Here’s a deeper dive into sourdough

Before we get into what sourdough is (or isn’t), it might be helpful to understand some of the terms around bread making, as these will help you understand the difference between what we define as modern and sourdough bread.

What is Fermentation?

In the context of food production, fermentation may more broadly refer to any process in which the activity of microorganisms brings about a desirable change to a foodstuff or beverage.

So the yeast acts upon the dough mix, releasing carbon dioxide gas, which allows the bread to expand, giving it the light, soft texture that we love.

Is all bread fermented?

Sourdough bread is a fermented bread.  However, commercial white bread that typically comes in a plastic bag from the local supermarket is also a fermented bread (as bakers yeast is a microorganism).

However, not all bread use microorganisms for leavening (ie, soda bread), and some breads don’t use a leavening agent at all (i.e. unleavened flatbread).

So, not all bread is fermented.

What is leavening?

The process of expanding the volume (size) of the bread is called leavening.  For commercially made (non-sourdough) bread, the leavening agent is usually bakers yeast.  However, leaving can also be produced using other leavening agents such as baking powder.  So, leavening and fermenting are two slightly different things.

What does the yeast do in bread?

OK, now back to our microorganisms.  Commercial bakers use bakers yeast (usually Saccharomyces cerevisiae), as it will produce desirable and predictable results in a relatively wide range of conditions, in a very short time.

The yeast acts upon the starch in the flour, increasing the yeast population, in a process called fermentation.  In so doing, it produces a number of by-products, the most obvious and useful one being carbon dioxide.

Sourdough loaf with a leaf design cut into the top.

Is yeast alive?

Yeast is a living organism found in the air, on our food, and in our bodies.   Like most life on our planet, it is sensitive to temperature, slowing and becoming dormant at low temperatures (fridge temperature), and killed at higher temperatures (around 55Ā°C).  There are some 1500 strains of yeast known to science, with some variation in the specific environments that the different strains prefer.  A few of them are quite useful in fermenting bread, beer, wine, etc.

Fermentation can also be achieved using bacteria (which are a little different to yeasts), with an example being Sauerkraut (or fermented cabbage).

A selection of breads using different grains and baking pans.
A selection of breads using different grains and baking pans

So why all this biology? 

Well, sourdough gets its name because of the mix of yeast and bacteria that act upon (or ferment) the dough.  This mix of microorganisms is responsible for (amongst other things) the delightful sour taste that we expect from a sourdough bread.  However, being living organisms, we need to provide the right environment for them to grow, and sufficient time to produce the desired results.

It should be noted at this point that different strains and quantities of microorganisms can affect the flavour, texture and smell of the bread.  This is something that beer producers often take advantage of in crafting beers that can have a broad range of characteristics, with specific yeast strains selected for specific beers.

What yeast do we use for sourdough?

So, if you are with me so far, there is just one more element we need to cover, and that’s the type (or strain) of yeast and bacteria used for a sourdough.   Our definition for sourdough is bread made from a mature starter, where the dominant yeast is NOT bakers yeast (ie. Saccharomyces cerevisiae), and with the lactic acid (produced by lactic acid bacteria from the starter) imparting the desired sour taste.

Sourdough starter, showing lots of activity with bubbles.

What is a starter?

A starter is simply a healthy population of the yeast and bacteria, that we grow (by feeding) and maintaining over time.  A starter is typically a mix or microorganisms, including yeast(s) suitable for bread making, and lactic acid producing bacteria.

Over time, the starter tends to produce an environment, that favours other strains of yeast.  The strain that we think of as Bakers yeast, gets crowded out by other strains that enjoy the acidic (ie. low pH) environment of your starter.

When we make bread, some of the starter is used to inoculate the dough (instead of using bakers yeast), and the dough is left to “prove”.

In conclusion

We love bread, and both make and consume it from all of our defined categories.   For many of us, and for much of our history, bread is a staple food, that is often part of our culture, and usually part of our diet.  It does seem to have been caught up in recent food fads, and we see lots of information (and some misinformation) about what sourdough bread is, and how to make it.

Although there is lots of science around bread making, its still a reasonably simple process that generations before us have been able to do without all the fuss of modern appliances, schedules, and hours of research on the internet.

With a little guidance, we think bread making should be enjoyable and satisfying- and usually very tasty.

We think Wiki has excellent definition of sourdough bread

“Sourdough bread is made by the fermentation of dough using naturally occurring lactobacilli and yeast.

It usesĀ biological leaveningĀ rather than using cultivatedĀ baker’s yeast. TheĀ lactic acidĀ produced by the lactobacilli gives it a more sour taste and improved keeping qualities.

Want to know more?

Would you like to learn how to make Easy Overnight Sourdough?

Easy Overnight Sourdough


    1. Hi Sue, I don’t have a book as such, I have an online course. The course is online and has lessons and downloadable recipes and templates. You can start the course whenever you like and go back to the course as often as you like. I figure once you’ve learned this method, it’s so simple you’ll only have to revisit the recipes which you can download to paper if you like. Here’s a link if you’d like to take a look.

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