If you don’t ‘feed’ a starter, how does it keep going?

What to do

[See also pages 165-166 of Bread Matters.]

Sourdough is (and always was) a self-perpetuating dough leavening system. In the days before baker’s yeast – or shops, for that matter – if you ran out of starter you’d have no bread, or pretty heavy loaves at best.

There are three stages to a basic sourdough baking system:

  1. The Starter – the small quantity of dough that contains a reservoir of live yeasts and bacteria. Between uses, this is kept in the fridge. It doesn’t need ‘feeding’. It can last, unused, in the fridge for years.
  2. The Production Sourdough – a mixture of a small amount of starter and much larger amounts of flour and water. Over several hours, the yeasts and bacteria in the starter, augmented by more of the same from the fresh flour, metabolise sugars in the flour into CO2 gas (the yeasts) and lactic, acetic and other acids (the bacteria). The gas raises the dough, the acids give it flavour (and a whole lot more).
  3. The Final Dough is composed of most – but not all – of the Production Sourdough plus flour, water, salt and any enrichments that the recipe may call for (fat, seeds, nuts, herbs, spices, fruits etc).

The idea is that you take some old starter, multiply it up to several times its size, let this ferment, then use most of it to make bread, keeping the residue to go back into your starter pot, ready to start the whole process again.

Take plain rye bread as an example:

  1. ‘Refresh’ the starter and thereby make a ‘Production Sourdough’:
    • Old Starter 50 g
    • Wholemeal (‘dark’) rye flour 150 g
    • Warm water 300 g
    • Total Production Sourdough 500 g
  2. Make the Final Dough
    • Production Sourdough 440 g
    • Dark or light rye flour 330 g
    • Salt 5 g
    • Water 200 g
    • Total 975 g

By using only 440 g of the refreshed production sourdough, you will be left with a notional 60 g to go back into your starter pot for next time. Thus the process goes on. In practice, you lose a little on the sides of bowls etc, which is why the recipe for the production sourdough requires only 50 g of starter, not 60 g.

Each time you ‘refresh’ your starter to make a production sourdough, you make about 10% more than you need for the final dough and that extra sourdough goes back into your starter pot in the fridge for next time. And so the process is self-perpetuating and your starter never runs out.

If you want to make a lot more bread one day and don’t have enough starter in the fridge, you can do a little ‘intermediate’ refreshment to bulk up your starter. If you like precision, you can do the maths and work out exactly how much starter you need to refresh to arrive at the right amount for your purpose (see ‘I’m making a big batch of sourdough bread. Do I need to alter the proportions of Production Sourdough to Final Dough?’).

The important thing to note is that your starter pot will, over time, contain the residues of many different batches of refreshed sourdough (i.e the left-over bits that are not used in the final dough). This is fine. Just mix the newer with the old and leave it all in the fridge (in a reasonably well sealed plastic container, not a glass jar with a metal strap) until you next want to make bread. No need to throw any away. No need to worry about ‘feeding’. You probably have better things to do with your life than fuss unnecessarily over a starter.

NB. The ingredient proportions and timings given above are for a pure rye bread. They are a bit different for wheat breads. But the principles are the same.