Making sourdough might seem like an absurd thing to get into but, if you can get the hang of it, the reward is a regular and cheap supply of really delicious bread. Frankly, who can argue with that? I’ve been inexpertly doing it for a couple of years now and I persevere not only because it tastes great but also because it does become a bit of an obsession. (Like that makes it OK somehow…)

There’ll be four parts to my ramblings about bread, because I can’t think of a more succinct way of doing it. I’ll look a bit at the science of how bread works because I think it’s useful to know about; ponder the question of what the best books are on the subject of sourdough; deal with making a starter or leaven; and, then, in the last part, I might actually say something about making a loaf of bread.

Two things about sourdough tend to be off-putting: it takes a long time from start to finish and it entails having to keep a bizarre yeast culture ‘alive’. I’m not going to say that those things aren’t true because they are, but you just have to embrace the weirdness. You get used to it. Ever wanted a few tubs of pungent fermenting flour and water kicking about the house? Well, now’s your chance.

A sourdough starter is a bit like a cat. It likes to be allowed to settle in a warm place for a while. But you shouldn’t let it get too comfortable: don’t be afraid to chuck it out in the cold every so often. You can even neglect it for long periods of time and revive it when needed (which, although I’m no cat expert, is perhaps where the analogy falls down a little).

Also, it’s educational: making sourdough well is much more about having sensitivity to the science behind the processes you set in place than it is about following instructions. So, it’s good for people who are a bit contrary but quite patient.

Conventionally in bread-making you add yeast to flour and water and, once you’ve left your dough to prove in a warm place, you find that it magically becomes big and aerated, ready to be baked into shape. The yeast cells, activated by water and warmth, have begun to digest the carbohydrates in the flour. Fermentation has taken hold, producing carbon dioxide and alcohol as the sugars break down into simpler molecules. Tiny carbon dioxide bubbles give the loaf its volume and texture, but are only useful if they can remain held within the structure of the dough. This is the function served by kneading: it helps to change the molecular structure of proteins in the flour, creating an intricate lattice that allows the dough to trap gas and then expand during proving and baking.

What makes sourdough different is simply that you use ‘wild yeast’ rather than yeast that you’ve bought in a shop or been given from behind the counter at Asda. Pretty much every foodstuff, including flour, already has some yeast-like bacteria living on it, while anything exposed to the air will pick up other useful beasties over time. These naturally occurring bacteria can be harnessed (again, my cat analogy seems not so appropriate… think about harnessing and saddling up a cat) and used as the leavening agent for your bread. Intriguingly, since the bacteria originate from the flour and from the air, they are locally specific, so you can legitimately claim to be baking from your ‘Deptford culture’ or whatever it might be.

Some of the bacteria are yeasts that act in a similar way to those you get in commercially bought bakers’ yeasts. They help you to ferment a mixture of flour and water. But others, such as lactobacilli, do rather different things and end up being really important in giving sourdough its distinctive taste.

When you use flour and air as your source for wild yeasts, they exist in very low concentrations at first, so this is where you need to give time to let them develop. In warm, wet conditions, yeast not only feeds (bringing about fermentation) but it also reproduces. The trick, then, is to give the naturally occurring yeasts the right conditions to multiply and create a source of cells lively enough to help you make bread.

Cunningly, the longer you leave a dough or any flour and water mixture lying around, the more of a sour taste you get from using it to make bread. While fermentation takes place and the yeast does its thing, the lactobacilli from the flour and the air help to produce acetic and lactic acid. Even in yeast bakery, doughs are often left for a long time to ferment (as a ‘sponge’) in order that some of these acid-producing reactions have time to take place and give the bread more flavour.

Yeast action will be slowed down in an acidic environment so, when you do intend to leave dough to prove for a long time, there is always a balance to be struck between maximising fermentation and yeast reproduction on the one hand, and allowing acid production on the other. Slow proving is often done at lower temperatures – in the fridge even – so that you can manage the balance more carefully and not end up with an overly acidic mixture where yeasts will find it hard to reproduce. Wild yeasts in sourdough starters are usually better suited to surviving in acidic environments than bakers’ yeasts introduced to the mixture.

(To be continued…)