Sourdough Culture – What’s in it?

One of the questions I am exploring as part of writing a guide on Sourdough cultures is “what is in a typical sourdough culture?”

Magic? No. Micro-organisms? Yes. Lots of micro-organisms; numerous strains with long latin names.

But broadly speaking there are two micro-organisms – wild yeasts (the “yeasties”) and bacteria (the “beasties”). Although an over simplification, it serves the purpose when thinking about what is in a sourdough culture.

The Beasties [Lactobacillus]
The Yeasties (Wild Yeast)

It’s a symbiotic relationship between these two micro organisms – the yeasties and beasties – and both find nourishment in a sourdough culture of flour and water.

The yeasties and beasties originate from the flour (the berries of wholewheat rye for example are teeming with life long before you add water), the hands of the baker, and the locality in general.

Once water is added to the flour, natural enzymes break down parts of the flour into sugars, and yeasties eat these sugars and produce carbon dioxide and alcohol; beasties eat a different set of sugars, and likewise produce carbon dioxide along with excretions of lactic & acetic acid. The bubbles of carbon dioxide are what rise the sourdough, whereas the acids give sourdough their aroma and flavour. Lactic acid is the milder and more subtle of the two; acetic acid is stronger (think vinegar) and makes for some super sour sourdoughs.

Wild yeasties and beasties are slower rising a dough compared to commercially manufactured yeasties (dried yeast, fresh bakers yeast etc), who represent a singular strain of yeast with no symbiotic beasties. Commercial yeast will rise your bread quickly, but it is the poorer for it. Interestingly enough commercial yeasts are no stronger than wild yeasts, indeed if you were to add commercial yeast to a sourdough culture, the commercial yeast would not take over, rather the wild yeasties and beasties would oust the commercial yeast, who can’t hack the environment these strange sourdough micro-organisms thrive in.

Temperature affects the micro-organisms in a sourdough culture – 28-30deg is an ideal temperature for a starter to flourish in a symbiotic nature. A cooler temperature (say extended periods in a fridge) will favour beasties and yeasties that thrive at lower temperature creating more acetic acid and resulting in a super sour sourdough. However lactic acid producing beasties like it best a bit hotter at 32-33 deg C the end product being a more subtle sourdough. During the baking process all micro-organisms will die, and the alcohol produced by the yeasties will be burned away, but by this time the work has been done transforming flour, water and salt into a tasty digestible loaf.

So that’s what’s in a sourdough culture – yeasties and beasties. A new starter in its infancy will typically have a rich micro flora, with lots of varying strains of yeasties and beasties all vying for dominance. But as your culture gets older and more established, with a consistent feeding and temperature regime, you will find a certain local strain of both yeasties and beasties will come to dominate the culture.

Which is one of the wonderful things about sourdough cultures – they are all a bit different.

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