Sourdough bread resists mold, unlike conventionally leavened bread. Now Michael Gaenzle and colleagues of the University of Alberta, Edmonton, show why. During sourdough production, bacteria convert the linoleic acid in bread flour to a compound that has powerful antifungal activity. The research, which could improve the taste of bread, is published online ahead of print in the journal Applied and Environmental Microbiology.
Sourdough is the best bread value.
I’ve always loved the tang of sourdough. My mother used to have a starter culture going when she would sometimes make her own. This continuously fermenting culture was just cool to watch and smell.
That is because sourdough does not simply use yeast to produce the gas that gives the bread its pores. It also has a mix of bacteria that work in conjunction with the yeast to metabolize some of the starches in the flour.
In the old days, the mix of yeast and bacteria were collected in the wild, thus making every starter mix slightly different. But these starters could be extremely stable, lasting for years if replenished. The starter culture used by the Boudin Bakery in San Francisco is the same one created in the mid 1800s. Over 150 years of continuous culture.
New bread would be baked by removing some of the starter and adding to fresh flour and water. Before baking, some of this dough could be used to create further loaves, saved to start some later or shared for others to create their own starter cultures.
The presence of certain lactobacillus helped give the sourdough its wonderful flavor. In an era before preservatives and refrigeration, sourdough cold result in consistently good bread because of the constancy of the starter culture. Keeping that culture alive became an important aspect of a baker.
One of the byproducts of yeast fermentation is lactic acid. The lactobacillus can use lactic acid to survive. In a measure of reciprocity, the lactobacillus can also metabolize a host of sugars that yeast cannot, giving the yeast byproducts it can use. A culture with both can live much better than either alone. This symbiosis helps explain the long term vigor of a good sourdough starter culture.
These starters could easily survive hardships such as freezing. That is why sourdough is often associated with gold mining in California or Alaska. If you had a good starter culture in a bag around your neck, all you needed was flour and water to make bread.
Well, now one of the other benefits of sourdough – it doesn’t get moldy as fast as normal baker’s yeast bread – has been more clearly delineated. It turns out that the lactobacilli in the bread produce several forms of fatty acids that inhibit mold and fungus growth.
What the researchers did was to examine some of the metabolic products of lactobacillus found in sourdough. They found that the addition of linoleic acid (found in sourdough) to the culture produced strong antifungal activity. This was due to specific fatty acids which they were able to determine were in high enough concentrations in sourdough to have a strong antifungal effect.
They were able to show that the presence of the lactobacillus, or the addition of the antifungal fatty acids, increased the mold-free time from 2 days to more than 6 days.
So another reason to buy sourdough bread – it will last longer before becoming moldy. It will save you money.