I’m in the process of making sourdough bread for the first time, which is very exciting. Exceedingly slow, but exciting!
If you’re unfamiliar with sourdough, it is simply a form of bread-making that makes the most of naturally occuring yeasts found in flour. The only two ingredients you absolutely have to use to make sourdough bread are flour and water. The rest is biology magic.
To start the process, the baker in question just needs a sourdough starter made of a flour and water paste, which is then ‘fed’ with top-ups of flour and water on a daily basis until the mixture becomes frothy. This frothy starter can then be used as the key ingredient in any sourdough recipe. Easy peasy! Well, sort of. I believe it can be a bit of an art… I haven’t got to the actual baking bit yet.
Leaving the art aside, the scientist in me couldn’t resist doing some research! So I’ve just spent a happy few hours reading scientific papers about sourdough.
Here’s what I found out:
First of all, sourdough baking has been around for a long time! Murals show Ancient Egyptians making sourdough bread, but it may well pre-date even them, they were just great recorders of daily life.
I don’t have access to a free image of Ancient Egyptians making the bread, but here are some women carrying some bread (probably):
This drawing of an Egyptian artwork, which comes from a guidebook from 1885 called ‘Egypt: A Handbook for Travellers’ by Karl Baedeker.
I love the idea of sourdough being a tradition that goes back millennia. Now that I’m attempting my own, I feel connected to all those (probably) women baking bread for their families, going back century after century. Its long history also shows that, despite all the complex microbiology going on behind the scenes, sourdough bread can’t really be that difficult to achieve. Can it?
… Yes, there may be times when your sourdough starter dies or is contaminated, but just make another or steal one from your friend. That’s what they would have done centuries ago.
I’m taking hope from that!
So back to the science… Although we generally think of bread-making as being achieved by yeast – the yeast make the high volumes of carbon dioxide we need for the bubbles – what we actually have in a sourdough starter is a little ecosystem of both yeast and bacteria. In fact the ratio of bacteria to yeast is about 100:1. Although, of course the bacteria are tiny in comparison to the yeast cells.
This is where I have to admit that I didn’t make a note of my references. I’m out of practice! If you’re interested in where I found specific information, just ask in the comments, and I will find it and send you the link.
To date, scientists have isolated more than 50 species of bacteria and over 25 species of yeast from sourdough starters around the world. However, a few are far more common than others, like the wonderfully named Lactobacillus sanfranciscensis. (It’s named after San Francisco, which is famed for its sourdough, and it’s in San Francisco that the bacteria was first discovered).
The bacteria are called Lactic Acid Bacteria (or LAB or lactobacillus for short) because they make lactic acid, and they come from a small group of bacterial families. These LABs are hardy types, they can cope with changes in water availability and even starvation, and may be rod-like or spherical. You will have come across them before – they are generally called ‘friendly bacteria’ in yoghurt adverts.
As an aside, I’m not a massive fan of the ‘friendly bacteria’ language. When I was a child, I believed vegetarians shouldn’t eat bacteria because they were a kind of animal! But a bacteria is about a gazillion* times less complicated than a plant, and nobody has a problem eating them!
* Super scientifcally accurate.
Hurray for the lactobacillus
It’s good to know that you’ll have LABs in your sourdough starter for a whole number of reasons. Not least, because they make a whole range of molecules which kill other bacteria and fungi that would spoil your bread. (They are still finding brand new bacteria- and fungi-killing molecules produced by these bacteria!) In fact, sourdough bread often has a better shelf-life than bread made with the kind of yeast you’d find in a packet in the supermarket.
The LABs do other interesting things too, like increase the solubility of magnesium in the bread, making it easier for us to absorb it, and increasing the folate availability. Scientists are still exploring all the affects that bacteria have on bread.
A happy family?
In many stable sourdough starters, a happy mutual ‘symbiotic’ relationship develops. The bacteria ‘eat’ the maltose sugar found in the flour (produced by naturally occurring enzymes in the flour which break down the starch into sugars). And because there is so much maltose, and because the bacteria are under stress, they just aren’t very efficient at making the most of it. So the environment begins to fill up with glucose as a waste product. Some yeasts can’t ‘eat’ maltose but can process glucose just fine, so they live off the glucose without competing with the bacteria.
That’s not to say that the yeast and bacterial strains are never in competition. It can be a bit of a melee in there. What allows the fight to continue is the fact that the baker is adding new flour and water every day, so there is enough food to go round. However, if you come back to the starter in a couple of years of daily tending, the composition of the starter may well be radically different. It may potentially look much more like a balanced symbiosis.
A stock photo of (possibly) sourdough bread… it certainly looks rustic. The wheat field is also a stock photo. Thank you wonderful pexels.com.
Why is my bread different to your bread?
Because every bacterial/yeast strain (and every interaction between strains) is different, a whole range of properties of your bread will be affected – acidity, viscosity, mineral availability, amino acid content, flavour/aroma molecule composition, carbon dioxide volume, and so on. The best thing to do is embrace the variety! Your strains will be the ones best suited to your flour, the temperature of your house, how often you feed them, and so on. Who said food had to be uniform?