On the Nature of Pre-ferments

One of the toughest things I’ve had to figure out when learning to bake is what should pre-ferments actually look like when they’re ready to use.  This goes for both the poolish or biga type ferments which are called for with certain French or Italian breads and pizza, but also for sourdough.  So I thought it might be helpful to take a few pictures for your interest, reference and constructive criticism.

Firstly, let’s think about poolish vs. biga.  Poolish is a wet pre-ferment, containing the same weight water and flour (ie. 100% hydration in bakers’ terms), it contains less yeast than a dough and should be left 12-16 hours to ferment prior to use.  Biga is a drier pre-ferment (70% hydration, ie. 70g water to 100g flour), which is in some ways a fermented dough.  As it is going to be left for some time, and the yeast will be slightly held back by the dryness.  For a day-before-bake pre-ferment, I use degassed tap water adjusted to 24ºC using boiling water from a kettle.  There is no salt in my pre-ferments.   I degass British tap water by leaving it overnight with a loose lid, so the chlorine can escape.

Just like a dough, your pre-ferment will grow.  Don’t forget to use a container bigger than your need (eg. 4-fold larger)


A couple of days ago, I made a large poolish to prepare Pain Rustique for the local homeless shelter.

Example Poolish:

In this example poolish, I fermented 6.5kg of Shipton Mill strong white flour with  6.5kg of water, and 1tsp of Doves Farm quick yeast.  I actually mixed it together in a spiral mixer for about 1 minute and medium speed, and left it to ferment for 16 hours in a plastic beer container.  You can see from the “time lapse” photography, the poolish grew by about one quarter in the first 6 hours, and by the morning, had nearly doubled in volume. Stiffer pre-ferments will hold their structure better and can increase in volume several-fold.

Quite a few things are going on in a poolish, but among other things the flour particles are getting fully hydrated, the yeast is producing a lot of flavour, gas is being produced, and the fermentation develops the gluten.

But – how do you know it is “working”?  You will take the lid off your container, and it will almost be alive with movement.  Bubbles will be reaching the surface, and it will not be still.  If you give the poolish a stiff knock – quite a few bubbles will appear.  I’ve taken a photograph of a poolish this morning as a reference.

Example poolish surface:


Rye Sourdough Mother

Now let’s take a look at a rye sourdough mother, of the sort you might use in Pain au Levain or 100% Rye bread.

Example Rye Sourdough Mother:

In this example, I’ve refreshed a rye sourdough mother.  I’ve taken about 10g of a rye mother from the fridge, and added it to about 100g organic rye (Cann Mills), and 100g degassed water.  I leave it on the counter overnight (17-19ºC) in this neat Sisteam plastic pot.  I’m mixing it up using a silicone spatula, in a polypropylene bowl, all of which makes cleaning up really easy.  You can see the air bubbles which have formed.  The mixture is really stiff, and doesn’t flow (over a minute).

Stiff Rye Sourdough Mother:


This close-up shows my rye sourdough mother not flowing.  Interestingly, a more liquid rye starter will favour certain fermenting beasties over others – and can lead to a fall off in the number of Lactobacillus sanfranciscensis which I tend to think of as a sourdough bakers replacement for Saccharomyces cerevisiae.  In my hands, a flowing rye sourdough mother leads to loaves which don’t hold their shape – that also flow outward, probably due to overpopulation of the ferment with bugs that digest gluten.

Liquid Levain

This is an example of a liquid levain, straight out of my fridge.  You can see that it flows.  This was seeded from my stiff rye mother, and its about 130% hydration strong white flour.  This is a liquid culture of yeast (funghi!) and bacteria, which will be a very different population to the stiff levain above.  My favourite Pain au Levain recipe utilizes both stiff rye mother and liquid levain mother, hence, maintaining the two cultures allows a more diverse set of microbes to ferment your bread.  At a later date, I’m going to blog on the diversity of microflora in sourdough mothers, taking academic publications and reviewing them in plain(ish) English.


Waste and Want

On a domestic level, it may feel plain wrong throwing out spare sourdough culture, or the end of an unused poolish.  If you happen to be making pancakes, throw in some spare sourdough – it adds character.  If you are making a yeasted bread, consider doing the same. I find my poolish keeps fine in the fridge for a week, and on the counter fermented dough in a sealed box is fine for several days.  Likewise, you can easily reduce the volume of rye sourdough you keep to a minimum (eg. 100g) which also reduces waste.


About jonnyr9

I'm an enthusiastic amateur "scientific" cook and baker, and former scientist, and I like to bring scientific thinking to my cooking: thinking about what might be happening at a chemical or biological level during food preparation (including its growth, and preservation), and applying exact methods of mass and volume to core recipes, before varying them. I use an accurate weighing scale (to 0.1g). I like growing my own herbs, constructing my own raised beds, and constructing my own wood-fired pizza oven. I bring a certain level of OCD to the kitchen, and therefore my baking includes sourdough, and my pizza-making includes "reference" to the protected specifications for true pizza. If I can source "the right" ingredients for a dish, I will at almost any length (within reason) - before I find an equivalent in-country supplier. Therefore - if you've never eaten Lancashire cheese bought at Bury market near Manchester - you've never eaten Lancashire cheese. I'm going to try to include links to the same products I use in my blog, so my readers don't end up using sub-standard alternatives - "experimental replication" is key to scientific cooking. I was born in the North of England, but I live in the South, though I would prefer to live on an island in the Ionian Sea.
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