Bread and Microbes


I found some slightly mouldy bread in the cupboard, cut off the mould and made toast. And I thought about bread and microbes.

For flavour, not as a raising agent, I make sour dough. My method is simple: I mix rye flour with water in a glass, cover it with cling film and put it on the countertop for a week or so. Lactic acid bacteria soon colonise the mix, lowering the pH to make the environment cosy for themselves and deter any other opportunistic microbes.

When the sour dough smells like vinegar I make bread dough with it, adding a second microbe: yeast fungus. The yeast eats sugar in the flour that the lactic acid bacteria haven’t had time to gobble up, and then it emits carbon dioxide gas, causing the bread to rise. (Rubbery gluten protein in the flour makes sure tenacious bubbles form instead of the gas seeping out of the dough.)

Then I bake the bread, which kills off the bacteria and yeast. After 50 minutes at 225 C, the bread is sterile. And delicious! But after a week or so, the bread gets recolonised by microbes, unwelcome ones. This time its another group of fungi, blue-green mould. Tastes awful, so I cut those bits off.

And my toast? I ate it all, sending it straight into the greatest throng of microbes it had ever encountered: the symbiont bacteria in my gut.

Author: Martin R

Dr. Martin Rundkvist is a Swedish archaeologist, journal editor, skeptic, atheist, lefty liberal, bookworm, boardgamer, geocacher and father of two.

3 thoughts on “Bread and Microbes”

  1. Making things look, smell, and taste yucky to us macroorganisms is the microorganisms’ means of winning the competition for those islands of food that we both compete for. Of couuse we’ve come to like some of those tastes up to a point and regularly consume partially decomposed foods. Enjoy.


  2. As far as I know it’s a bit of gamble just to cut the part with visible mold of a piece of bread. Nevermind that most of the mold isn’t visible but there’s also the risk of mycotoxins. At least that’s what I learned in basic hygiene when I was getting my permit to prepare food comercially. But hey, it’s your funeral 🙂 And I’ve for sure eaten a lot of stuff like that as a kid when people around me didn’t know any better – both bread and fruit jam where the mold was just removed.


  3. The gut bacteria might need a bit of help.
    Hybrid commensal bacteria for the human gut that can split cellulose into simple sugars would make you able to survive of a diet of sawdust.
    I have been thinking a lot about “hybrid” DNA to make more food available. The simplest would be things like making cassava/maniok that contains no poisons, so you can eat it without the heavy processing. Hirs and durra are hardy crops in the third world, but are not (yet) as productive as the crops mainly consumed in the North.
    But the most useful option in a world obsessed with meat would be engineering vegetable or bacterial matter to get the taste and texture of meat, feeding the demand without cutting down the Amazonas for cattle.


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