Could 100-year-old sourdough be a myth?
Forgive the pun, but sourdough is on the rise. Speciality bread producers are defying the recession to sell loaves with the unique, tangy flavour that differs from bakery to bakery. But can starters some use really date back hundreds of years?
Sourdough still retains an aura of mystery and superstition dating from its birth 5,000 years ago in ancient Egypt.
But these days its bakers develop near-parental relationships with their own leavening cultures that must be regularly fed and nurtured.
And even though a starter can be knocked up at home for pennies from flour and water, some people still choose to buy a starter with a history.
Sourdough cultures can be bought online from countries around the world; from San Francisco to Moscow.
Freeze-dried or fresh cultures can be ordered for next-day delivery, allegedly enabling the home cook to re-create a unique sourdough flavour that stretches back decades and across oceans.
But do these stories of historical provenance really hold up against scientific evidence?
Dr Marco Gobbetti is one of a team of microbiologists at the University of Bari in Italy, who specialise in sourdough culture research.
"Yes, I know that several people claim to have stable sourdoughs for decades," he says.
"In my experience, this is extremely rare. Obviously, under these conditions the technology and environmental conditions have selected very strong cultures.
"Very old cultures, if they really persisted, have to maintain almost unchanged."
End Quote Fergus Jackson Brick House bakery
You could make a cracking sourdough in a week or less”
Dr Gobbetti's work, published in the Journal of Applied and Environmental Microbiology, showed that environmental conditions can completely change the blend of bacteria and yeast that live in a sourdough starter.
Dr Bill Simpson, microbiologist and managing director of Cara Technology, tests and monitors yeast quality for the brewing industry, and has seen this first hand.
"If you take this sourdough culture and move to Tunisia and start baking there in the ambient temperatures, if we tested the culture after a few months, we'd find something very different," he explains.
"The strains that currently serve you well, they would begin to be lost and other strains that are there in the background would start to do well."
The taste fingerprint of each dough is utterly unique to its home.Microbiological romance
Sourdough starter, or culture, can be made from two ingredients: flour and water.
Add time and warmth, and soon the sloppy dough turns into a bubbling, acidic, beery-smelling gloop that is capable of raising double its weight in bread dough into a bouncy loaf with an unmistakeable tang.
When sourdough culture is placed under the microscope, however, a love story emerges between two types of microorganisms: yeasts and bacteria.
- American author Jack London described how Alaskan gold-miners kept sourdough starters alive in cold conditions by sleeping with them
- The acidity of sourdough kills off ergot spores. Fewer cases of ergot-induced hallucinations are reported from medieval Germany where the sourdough process was favoured
- Lactobacillus sanfranciscensis, was identified in the 1970s as the key to the San Francisco sourdough's distinctive flavour. However the same bacteria is also found naturally in Italian and Greek sourdough
The natural yeasts found in flour grow in symbiosis with lactic bacteria, like those found in yoghurt, sharing food and fighting off competition from other microorganisms in a harsh, acidic climate.
Dr Simpson says the strongest sourdough cultures are those with one dominant yeast strain and one dominant lactic bacteria strain.
"It's like two partners in a marriage. They're perfectly matched for each other, so any interlopers don't stand a chance," he says of the strains.
When the culture contains many varieties of bacteria and yeasts, the bread produced can be less consistent, as he found in a laboratory sample.
"In this sample, they're still playing around, they haven't really quite decided yet."
In addition, the ambient temperature, water content, and time between feedings all play a part, as does the flour used in feeding, says Dr Simpson.
"It contains yeasts, it contains bacteria, and you'll introduce those into the dough."
The science proves, even with the tightest controls, which are not within the gift of the average home cook, the balance of microorganisms change.
Another study from Dr Gobbetti's team showed that two samples of the same sourdough propagated under the same conditions grew differently when they were stored at a bakery or a laboratory.
The different locations "changed the composition of the lactic acid bacteria and especially the yeast".From lab to bakery
Bakers are divided about what variation in the culture really means.
Fergus Jackson runs London's Brick House bakery and doesn't believe in the myth of far-away loaves.
"I learned my craft out in San Francisco and had considered bringing back my starter and using it as a selling point for my bakery. But I decided against it as I knew it would be a bit of a lie," he says.
Starter for 10
- Starter: A mixture of flour and water in which natural yeasts and bacteria grown to produce a thin, bubbly mixture that is regularly fed with more flour and water
- Levain: A fully matured starter that is used to make bread, or a portion of unbaked dough saved from the previous day's bread
- Poolish: A batter-like dough with a little yeast that is fermented for a few hours to improve the flavour of bread. Also called a sponge or a biga in Italian, though a biga can also be firm
He admits that "stories of ancient starters fuel the imagination and make the product more desirable", but does get annoyed with the "whole sourdough mythology".
"If you read all the stuff online you'd think that you'd need to nurture something for years to get a truly decent sourdough loaf, when in reality you could make a cracking sourdough in a week or less."
However Andrew Whitley of the Bread Matters baking school near Edinburgh considers his sourdough starter, brought back from Russia in 1990, to have retained its essential properties.
"In 22 years of using and refreshing my Russian starter I have never once had a 'failure', nor have I been able to detect any drift of flavour," he says.
"Laboratory analysis might tell a different story, but bakers live in the real world of daily production and over the millions of loaves I (and others) made with my Russian starter no-one complained about any change attributable to the sourdough."
He describes being approached by a salesman from a bacterial culture company who offered a powdered starter that would give better consistency.
End Quote Richard Bertinet Bertinet Bakery
It feeds the soul as much as it feeds the stomach”
"I demurred, saying that my starter, despite being refreshed with UK flour, didn't seem to have changed much."
After a month of testing, the salesman returned, a little chastened. "The graph he presented showed two lines running exactly parallel about a millimetre apart. He correctly predicted that I wouldn't be in the market for his powder."
Richard Bertinet of the Bertinet Bakery in Bath also credits romantic stories with the success of sourdough.
"I think the important thing to remember is that there is a difference between the chemistry of it and the romance of it," the baker says.
"Much of the appeal of sourdough is the heritage and history of it - tying your baking to family and community and passing it on (in the form of your sourdough culture) to other bakers. It feeds the soul as much as it feeds the stomach."
Andrew Whitley says the revival of sourdough is down to its taste of "just the best bread in the world".
"It has a texture, and a flavour - a sort of bready, resolved, rounded, ripe flavour that is not available to fast-made yeasted breads. And many people over the years have revolted against the bland uniformity of industrial sliced bread."
Diversity is the essence of sourdough, and its difference from culture to culture will continue to be the source of its mystery.