Are you starting to make sourdough bread for the first time? Before you get to this stage, you may have a lot of questions about sourdough production, including how much sourdough to discard. Indeed, natural sourdough is maintained by regularly refreshing it by adding fresh flour and water. This is called the refreshment stage. And with each refreshment, you need to discard some of the sourdough before feeding it again.

In this guide, we’ll explain how much sourdough to discard at each refreshment and why this step is essential, so that you understand the importance of such a step.

How much sourdough should be discarded?

When refreshing, we generally recommend keeping only a small portion of the sourdough and using the rest elsewhere. In practice, this means discarding around 50-80% of the sourdough before re-feeding. In other words, you keep 20-50% of the sourdough and replenish the rest with fresh flour and water.

For example, if you keep around 20% sourdough and discard 80% with each refreshment, you get a 1:2:2 feeding ratio (1 portion of sourdough for 2 portions of flour and 2 portions of water).

However, there are no absolute values, as the quantity of sourdough is specific to each individual. As you will see, adapting the quantity of sourdough will, among other things, enable the bread to change taste. It is therefore advisable to try several ratios to find the one that suits your taste.

Why is it necessary to discard some of the sourdough?

As you can see, discarding some of the sourdough is important, but how much is up to the individual baker. But what are the reasons why bakers eliminate some of the sourdough?

Although it may seem counter-intuitive, discarding is vital for the health of the sourdough. The reasons are both biological and practical.

To avoid excessive acidity

First of all, it’s important to discard part of the sourdough to avoid excessive acidity, because the longer a sourdough ferments without the addition of flour, the more acids (lactic and acetic) it accumulates. Without this operation, the sourdough would become increasingly acidic, which can weaken the yeasts (they ferment poorly in too acid an environment) and unbalance the microbial flora.

Replenish nutrients

Micro-organisms in sourdough feed on flour sugars. If you run out of flour, they deplete the resources and the sourdough starves. Not throwing away your sourdough at all would lead to an unmanageable sourdough mass over the long term, while obtaining an over-acidified, nutrient-depleted sourdough.

Maintain a healthy microbial balance

By discarding part of the sourdough, you avoid the excessive proliferation of undesirable micro-organisms. A sourdough that is too old, never “cleaned” by refreshing, can see its population shift towards acetic bacteria (acetic acid producers) to the detriment of lactic bacteria and yeasts, affecting its aroma and strength.

Manage volume and waste

Beyond the biological aspects, throwing away some of the sourdough serves to control its volume. Otherwise, the amount of sourdough doubles with each feeding. By keeping only a defined portion (e.g. 50 g), you maintain a reasonable amount of sourdough from one refreshment to the next.

This avoids ending up with unmanageable quantities (and having to waste even more flour). It’s better to maintain a small quantity of active sourdough than a large volume that stagnates.

Note that sourdough that has been withdrawn is not necessarily “wasted”: you can use it in other recipes, and it has leavening and aromatic power, similar to classic sourdough. Think about using it to make delicious preparations, rather than systematically throwing it away.

So, if you were wondering how much sourdough to discard, you can rest assured that the quantity remains individual, but that a value of between 50 and 80% is generally considered acceptable. Take the time to observe your sourdough, adjust the quantities and remember: discarding is also nourishing. A balanced, high-quality sourdough is the key to successful bread-making. Want to go further and expand your knowledge? Consider our natural sourdough bread training course.