Sourdough Starter

The first step in the perfect bread crusade

Difficulty: low Preparation: 10 minutes Unnatended: 7 days

Preparing sourdough starter is easy, but it requires some attention until it becomes strong enough to survive unattended in our fridge.

Before getting into the details, we need first to answer one important question: What is Sourdough Starter? Sourdough Starter is a mixture of equal parts of flour and water in which we grow both wild yeast and lactic acid bacterias.

But, where do I find some of those bacterias and yeast? They are everywhere. By mixing flour with water, we'll activate the natural yeasts and microorganisms present on it as well as the ones present in the environment. All kinds of yeast and bacterias will grow in our jar, but as the colony becomes older, the ones we need will become stronger and predictable. After about a week this process will stabilise.

And what is the benefit of using sourdough instead of yeast? Using sourdough starter instead of yeast will make your preparations (Bread, Pizza dough, etc...) have an amazingly intense flavour thanks to the long fermentation. This process will make your doughs more digestible as well as make them harder for it to spoil.

The only hassle is that the fermentation will take some time to happen contrary to the super active industrial yeasts. In my opinion, there is nothing better than the smell and taste of fresh sourdough loaf so... if you have the time, go fo it.

Sourdough Witchcraft

You have probably heard numerous controversial urban facts about sourdough starters which although funny, just add confusion to such a simple process.

Many of these facts contradict each other: Put grapes, apple, pears, potatoes, yoghourt... leave the jar in a closet, make sure the water is precisely at 28.5º... or the flour has been milled on the full moon.

Seriously, what we are trying to growth are yeasts that has been on this planet since the beginning of time and which will still be here after we leave it. They will survive to pretty much anything, so do not stress about it, please. Yes warm-ish is better than cold, and whole wheat or rye will have more yeast than refined flours, but that's it.

Last but not least: Should I close the jar lid?
- I've been told dreadful things could happen if I close it.
- I've been told that if I leave it open, it'll take over my kitchen!

It doesn't really matter. Regardless of what you have been told, most of the process will be anaerobic. Yes, if some Oxigen is present, bacterias in the surface will use it as it's an easier growth path... but if it's not, they won't.

If you want to read a detailed scientific explanation of the metabolic pathway that is going on in our jar, please read Lactic Acid Fermentation in Sourdough by Debra Wink, where you'll find a fantastic explanation of the science behind this process.

And no, if you leave the lid closed, your jar will not explode because of the produced CO2.

How to start a colony?

Put equal parts of flour and water in a jar and mix them together. About 50g of each is enough. Remember to close the jar with a lid. Your Sourdough starter is ready!

Colony needs

Our Sourdough starter has two basic needs. It needs to be fed periodically, and it needs to stay at a stable temperature. These two requirements will become less and less serious as our sourdough becomes older.

Approximately every 24h we need to fed our colony with enough 50:50 mixture of flour and water, so it doubles it's weight. Before doing so, it is a good idea to discard about 50% of the previous mass.

Why? To not end up with lots of it! If you do the maths, a dough of 100g (50g water, 50g flour) would require you to add almost 13kg of flour and 13kg of water by day 10 in order to double its weight.

dough mass = (100g * 2^(days-1))

Temperature needs to be stable and mildly warm during the entire process (20º-30º). Higher room temperature will speed up the development of the colony. Conversely, a cooler one will make it require more time to grow. The general advice is not to put it close to a window, as both the sun and air could mean drastic temperature changes, which might affect the sourdough.

Leaving it on the kitchen counter is a good idea as it'll allow you to remember to feed it.


Any non-refined flour would do. The less treated the flour is, the easier/faster our colony will develop.

You can use any water, including tap water. If the tap water in your region is high in Chlorine, it is recommended to use bottled water instead as the Chlorine will kill some of the bacteria we are trying to grow.


This is the schedule we'll need to follow

Step by step

Day 0

Once you have created your colony with 50g of water and 50g on flour, leave the jar unattended for 24h.

Day 1 to 7

Discard 50%, add 25g of flour and 25g of water. Remember to incorporate the ingredients fully.

As the days pass by, we'll start to see how the sourdough evolves from been practically static on day 1 and 2, to start showing some bubbles in day 3 and 4, to start to grow in volume after day 5. In a similar way, the smell will develop as the fermentation happens.

This process can take longer if the room temperature is too cold, or shorter if you are in a warm area. Regardless of how fast the colony develops, repeating this process for at least six days is recommended, so the final sourdough starter will be strong enough to survive longer periods of time in out fridge.

By the end of the process, our sourdough should be able to double its volume in 3 to 4 hours after feeding it. Its texture should be smooth like a mouse once this happens.


How much should I use?

Generally speaking, you can replace dry yeast with fresh yeast in any recipe using approximately three times more. Let's say your recipe calls for 7g of dry yeast; you could add 21g of fresh yeast instead. When using sourdough starter things complicate a bit because the mass of the starter is significant enough to affect the preparation.

How much should you put on a recipe depends on the preparation itself, and the room temperature where you'll ferment the dough. That being said, replacing 15-20% of your recipe with sourdough starter should be enough during summer, and up to 30-40% should work during winter. I encourage you to try to adapt your recipes using numbers in that range and experiment.

If your recipe calls for 500g of flour and 300g of water, and we want to use a 30% of 100% hydration sourdough (equals parts of water and flour). We need to calculate first the total mass of the preparation: 800g (500g+300g), then calculate how much starter we need: 240g (30% of 800g) and then simply remove from the original weights the amounts of flour and water we are incorporating because of our starter: 120g of water and 120g of flour (50% of 240g). The result would be 380g flour, 180g water, 240g sourdough starter exactly 800g of preparation like the original recipe.

How can I multiply my sourdough starter?

Once you know how much sourdough starter you need, (let's say 240g) you simply need to repeat the feeding process with enough ingredients, so your resulting dough is big enough for your preparation. If you had 100g of sourdough starter, mix 50g of it plus 95g of flour and 95g of water and in a bowl. After the fermentation (2 to 3 hours) you'll end up with 240g of sourdough starter (50+95+95 = 240g) ready for your recipe.



Once your sourdough starter is ready, you can store the closed jar in the fridge for weeks/months/years. The fridge temperature will slow down the process, so you don't need to feed your colony daily.

It is a good idea to do a one-off feeding every couple of weeks, so we keep our colony healthy. A yellow/brown liquid might appear on top of our sourdough, do not panic, this is just a by-product generated by our lactic bacterias, you can simply remove it.


You can freeze your sourdough in a closed container after feeding it for months. Once you are ready to use it, unfreeze it and do a couple of feed cycles, so we wake up our colony.

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