Humans have been harnessing the power of microbial fermentation by wild yeasts and bacteria to make bread for thousands of years.
Sourdough is a living community of microbes, chock-full of wild yeasts and acid-producing bacteria. The yeasts ferment sugars and make carbon dioxide, the bubbles found in most fermenting things. The bacteria take the sugars and starches and convert them into acids, which add flavour to the bread, and help it to be more digestible.
Most sourdoughs across the world are dominated by Saccharomyces yeast - the workhorse bread and beer fungus, as well as Lactobacillus bacteria, which are also found in products like yogurt. However, every sourdough is a little bit different and there are also oddball species of yeasts and bacteria present in different people’s sourdoughs, giving rise to different qualities of acidity and flavour.
Have you ever wondered how you can make your own sourdough? Has someone told you that you need to be living in San Francisco or some idyllic alpine mountain town to harvest good wild yeast from the air? I’m here to demystify making your own sourdough, and to assure you that you can make a sourdough starter pretty much anywhere in the world.
It can be as simple as mixing some flour and water and waiting for fermentation magic to happen. Or, you may end up baking a bunch of stinky pancakes.
You see, the microbes needed to make a sourdough starter are pretty much everywhere around us. Saccharomyces, Lactobacillus, and their other microbial friends have followed humans around the globe like little microbial pets. They are in the air we breathe, on our skin, and often even present in raw grains and flours. However, the microbial world is one of intense competition. Many different microbes battle for dominance in these tiny worlds, and this certainly can include a brand-new sourdough starter, which is essentially just some flour (whole grain, please!) and water mixed together. So, it can help to create some selective pressure for the right microbes to grow.
One genius trick developed by Debra Wink is to add acid to your first flour and water mixture, by mixing some pineapple juice into the initial, 50:50 flour to water mixture. This creates an environment where unwanted microbes will be outcompeted by the microbes we want to grow, since sourdough yeasts and bacteria are quite tolerant to acidity! By adding some acid right at the start of the process using pineapple juice, we lower the pH and ensure that the yeast and lactic acid bacteria we want to thrive do so.
So, making your own sourdough can be as simple as the following process, which I recently attempted using both whole rye and whole wheat flours.
Mix 2 tablespoons whole grain flour and 2 tablespoons pineapple juice in a small container. Cover loosely, so it doesn’t dry out, but still receives some air flow – Saran wrap with a couple holes poked in will work nicely.
Wait. After some time (anywhere from 1-3 days) you will start to see signs of life – small bubble in the dough! This means that a potential sourdough culture is starting to establish itself.
You can start feeding the sourdough once you see lots of bubbles. To feed your sourdough, I recommend a 1:2:2 ratio. This means that for every 25 grams of sourdough, I’m feeding with 50 grams of flour and 50 grams of water. Having a digital scale helps a lot here!
Observe the fermentation rate of the sourdough. How long does it take to triple in size? Keep feeding, until it is tripling in size within 8 hours. Usually, this process takes 7 days from the initial flour-juice mixture to a sourdough reliable enough to bake with. Once it is rising reliably, you can feed it with all purpose or bread flour.
Grow enough of your brand new sourdough to make a loaf of bread!
If you don't want to go through the process of creating a sourdough starter, there are commercial products available which give good results and can get you up and baking faster. You may also have a neighbour with a sourdough starter, so ask around!
How to Maintain Your Sourdough Starter
OK! So now that you’ve got a sourdough starter (either through our do-it-yourself guide, or from a generous friend), the next question becomes: how do I take care of this thing? To many, a sourdough starter becomes like a pet, requiring constant feeding and attention. There are even sourdough hotels where people can drop off their doughy pets while out of town. However, there are ways to make caring for a sourdough starter easy, and my goal here is to downgrade the level of maintenance from a house pet to a house plant. Really! Just like that neglected spider plant in the corner, with the right care your sourdough can be ignored for weeks at a time too.
Feeding a starter is simple: to grow enough sourdough to make a batch of bread, simply discard* all but a quarter cup of sourdough (about 25g) and then feed with equal proportions of flour and water: 50g (1/2 cup) flour and 50g (1/3 cup) water. You can scale this up or down as you please, maintaining a 1:2:2 ratio of sourdough starter, water, and flour. The starter should rise to double or triple in size within 8 hours if it is healthy – and often quicker, especially in the summer months! After it rises fully, it may drop or become more fluid – this is okay, but refrigerate if you’re not going to use it immediately. To test if it’s ready, take a small spoonful of sourdough starter and drop it in a cup of water – it should float. Don't worry if not, as long as it's bubbly that's a positive sign.
*Leftover sourdough can be used to make pancakes, crackers, and all sorts of delicious things.
In terms of which flour to use, I recommend using whole grain flour every third feeding, or as 1/3 of the feeding mixture. Note that whole grain feedings might not hold as much gas and so might be very active but may not pass the float test.
If you do not plan on making bread for a few days, you can reliably store a fed starter in the fridge for up to a month without feeding. When you need it again, make sure you feed it until it reliably rises again – sometimes the sourdough organisms need a couple feedings to come back to full strength! I recommend feeding at least once before using. This means that if I’m baking on Saturday, I’ll take the sourdough out of the fridge on Thursday evening, feed it, let it wake up (bubbles!), feed it again on Friday evening, and then it will typically be good to use for Saturday morning.
For long term storage, you can freeze sourdough. The microbes are quite tolerant of very wide temperature swings! So if you’re going away for an extended period of time, you can store a small bit of sourdough in the freezer (I’ve spread it thin on parchment and then crumbled it up). To revive, just let it thaw out then feed as normal. It might take a few extra feedings to perform like usual.
Troubleshooting Sourdough Starters
If starter does not pass float test, or produces loaves that are too flat and/or acidic: the yeast in the starter may have died. You can try feeding with a lower ratio of sourdough to new starter, or start over and make a new starter.
If your breads are turning out too acidic or too difficult to handle (falling apart), try fermenting for a shorter period of time (end of step 1) or refrigerating the dough until ready to shape/proof. This will help slow down acid production by the bacteria in the sourdough culture. This can especially be a problem in the hot summer months. The fridge is your friend, and can be used to slow down the dough fermentation, proofing, or any other step in the process.