Incr-Edible Science: Making a Sour Dough Starter

Our sour dough loaf
Our sour dough loaf

Laura Ingalls did not have access to the dried packet yeast that we all take for granted these days.  Instead her family would have made their own to use with flour and water to make a slightly different type of loaf to the one we eat.  The loaf was called sour dough bread and the yeast was created using the natural yeasts in the air.  Equal amounts of flour and water were combined and mixed and left in a pot or jar with a loosely woven material covering it.  This allowed the yeast, which is a single cell fungus and found naturally in the air, to land on the flour/water mixture.  The yeast breaks down the starches in the wheat flour and forms sugar.  As the yeast works on the starch and sugar molecules it gives off carbon dioxide and alcohol.  This process is known as fermentation and it is this reaction which makes yeast work as a leavening agent for bread making.  The Carbon dioxide production and further expansion in the heat of the oven makes the bread rise, much like the bicarb and acid reaction we learnt about to make soda bread:

C6H12O6 (Glucose,  sugar) yields  2  C2H5OH (Ethanol)  + 2 CO2

The gluten found in wheat bread helps the process along by trapping in the carbon dioxide and making those tiny holes we find in bread.  The gluten, a rather stretchy substance, is formed from two proteins, gliadin and glutenin.  When the dough is kneaded the gluten is forced into thread like chains which ultimately hold the carbon dioxide in.

Once captured the yeast is kept alive in this ‘sour dough starter’ which is fed every few days and used whenever needed.  The starter can be kept alive indefinitely in this way.  As the sour dough starter uses wild yeast from the air, each loaf will be distinctive in how it tastes, dependent on the type of yeast that is in the air when the starter is first made.

We thought we would give it a go.

We combined two cups of flour to two cups of water, gave it a mix, covered it with C10’s knitted cloth and left it in a warm place.  Apparently yeast floats in the air year round and hopefully some of this yeast (the discerning ones) would make their way into the ready food source we had laid out for them, where it would start growing and replicating:

Our sour dough starter, just starting out!
Our sour dough starter, just starting out!

It produced small bubbles almost immediately and the next day was happily fermenting away, with a frothy head.

Whilst it is not pleasant it does not look mouldy or like it is infested with a multitude of grim bacteria.  There are two reasons for this:

  1. The starch in the wheat bread flour is not compatible with most bacteria and
  2. The yeast poisons the culture with the alcohol it produces, which also keeps the bacteria out.

The next day we threw half of it away and added another cup of flour and one of water and stirred, thus ‘feeding’ the yeast.  Each time a liquid was seen at the top of the mixture (the hooch) it was stirred. Right now we are on day three.  Our kitchen smells a bit niffy and I’m thinking the children are not too impressed by the idea we’re going to end up eating the stuff.  I’m not even telling Gary.  He thinks it’s one of our experiments.  The ‘aroma’ is strong, bready, alcoholy and frankly more than a little bit yucky.

24 hours later
24 hours later

On day five, by which time it should have become a thick yellow liquid, our aim was to use one cup of the yeasty mixture to make a sour dough loaf.  Until this time we used pegs on our noses.

Well we actually managed just one more day,  24 hours short of the required 5 days.  The smell was horrible and was pervading the whole house.  So we made a small loaf of sour dough bread.  Now I’ve made bread for years and never measure anything so although I knew I could look up a sour dough recipe, I just went ahead and mixed a cup of the starter into some flour.  In all honesty it was probably too much starter for the amount of flour, but I didn’t care.  I wanted this bubbling mass of smell out of my kitchen.  I mixed and kneaded, having rubbed in some lard.  Here is our small loaf before rising:

Pre rising
Pre rising

I put it outside to rise.  It rose fairly well so I was quite hopeful:

Post rising
Post rising, believe it or not this is before cooking.

Once risen I baked it for 15-20 mins at 200 degrees.  This is the lazy persons method of bread.  It has served me well for years (although I usually use butter not lard – Laura and her family used lard so I copied!).  Whether it would serve us well on this occasion remained to be seen.  Oh, the smell whilst cooking was not good.  Definitely used too much starter!  Here it is after cooking:

Our sour dough loaf
Our sour dough loaf

Looks good, doesn’t it?  You’d think there would be a queue of tasters.  Surprisingly few of my children even wanted to try it, and looked at me very suspiciously when I attempted to show some enthusiasm.  For the sake of education I made them all try some.  We served it hot with maple syrup:

There it was...gone!
There it was…gone!

Our verdict?

I personally wasn’t too keen.  It has a distinctive acid flavour, which was to be expected.  The texture and smell were exactly the same as normal whole meal bread.  The children really, really liked it.  And Gary?  Well, he didn’t actually get to try any, the children had gobbled it up before I could save him any.  I’m sure he’s breathing a small sigh of relief somewhere.

A4 has her latest post out on how to make button lamps


  1. This is a great post. I just love how to explained it step-by-step, both the science and the practical how-to. My husband is from San Francisco, where sour dough bread is famous. He misses it so much, but it just doesn’t turn out as flavorful here on the east coast. You make me tempted to try again, however.

  2. I agree, this is a great post – loved the science of it – I didn’t realize that yeast is just floating around. I’m going to try this with the girls, and see if fermented Nova Scotia yeast is as smelly as yours 🙂 ( I laughed out loud when I read that your husband didn’t even know it was to be eaten)
    Do you think you’ll be making it again?

  3. As you may know, you can keep part of the starter and just keep feeding it to keep it going. Women in the South give it to one another. Perhaps that could be a way to get SF bread on the east coast… start with a SF starter from a friend or a trip, though I don’t think they’d let you put it in your carry on 🙂

    1. I like the idea that you are given a starter from a friend and pass some of it on to another friend, making it last indefinitely. However, it is the lasting indefinitely that I have an issue with. Surely nothing in life should smell THAT bad!

  4. I was just thinking yesterday about ordering some Sourdough Starter. Now that you’ve framed it as a science experiment I might have to give starting my own another try.

    1. Somehow I missed this comment, sorry Lucinda! I didn’t know there was yeast in the air either. I think there must be a higher than normal concentration in my house because it took really easily and quickly and worked a treat (I had heard it can be hard). I’m not sure what that says about my house though!!

  5. Huh, it sounds like you got some funky yeast in your starter. I have made sourdough starts before using packaged yeast, not wild. They have the typical fermentation smell that is reminiscent of beer, but I have never had one that is stinky or strong enough to smell up the house. If you try it again, maybe you would like it better if you “cheat” a bit and use commercial yeast to start. In fact, you’ve inspired me to go mix some starter up right now!

    1. If I tried it again I would probably completely cheat and go and buy a loaf from the local bakery!! Thanks for the information though, it’s always good to know what went wrong. The children enjoyed the taste of the bread even though I really didn’t. I hope yours goes well for you!

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