Why You MUST Discard Some of Your Sourdough Starter

You must discard some of your sourdough starter each time you feed it.

You'll discover that discarding is necessary to build a healthy and thriving sourdough starter - but it's not actually as wasteful as you might think.

Why You Must Discard Some of Your Sourdough Starter Before You Feed It

If you don’t discard your sourdough starter, it will grow too big and be unmanageable. Not to mention you will go through an unmentionable amount of flour.

Let’s say you start with 50g of flour & water on day 1.

If you don’t discard, by day 5 you’ll end up needing to feed your starter in excess of 300g of flour per feed (ie twice a day).

By day 10 this would increase to in excess of 800g of flour per feed. Crazy right. And it will just keep growing!

What Is Actually Happening When You Discard Your Sourdough Starter

When you create a sourdough starter, you are in fact creating a microbial population.

These wild yeasts and lactic acid bacterias living in your sourdough world feed on the sugars in your flours.

Through this feeding they create the bubbles that you see in your jar.

Their food is not endless and so eventually they will eat through all of the food your provided.

Some of the yeasts and bacteria will start to die. If your starter goes too long without food, it will start to make hooch and smell like acetone.

In order to allow your starter to grow and flourish, you need to "refresh" it with fresh flour and water.

Discarding some first allows you to add this fresh food, whilst maintaining your starter at a manageable size.

Not discarding your starter will also affect the flavor of your starter.

Not discarding before you feed will cause too much acidity which may eventually be detrimental to your microbes.

Why Discarding Is Not As Wasteful As You Might Think

It’s actually much less wasteful to discard a little each day while you’re developing your starter, than to waste a tonne of flour feeding a gigantic starter.

If you’re using all purpose flour, it’s like $1-2 for a kilo. I've built a starter using cheap, 99c all purpose flour and it's a fantastic starter, strong, flavorful and my absolute workhorse.

My All Purpose Flour Sourdough Starter is an absolute workhorse and never skips a beat.

Rye is also a good option for your starter, but to keep costs down you could use a blend of all purpose and rye - or just use rye when your starter needs a boost.

When Can You Use Sourdough Discard?

You can use the discard from your starter to bake, but it’s better if you wait at least 7 days before you actually use it.

In the first 5-7 days, it’s better if you bin or compost your discard because the bacteria will be fighting it out and it will generally smell pretty gross.

You probably won't want to use it during that stage.

When you are ready to use your sourdough discard, I highly recommend this recipe. Alternatively, you can store your sourdough discard in the fridge or add your sourdough discard to any recipe you like. These sourdough snack ideas are a fun way to use up discard too!

Once Your Starter Is Mature Things Change

Once your sourdough starter is mature, you do have options and you won't need to discard in the traditional sense.

Just a note before I explain the above concept - your starter will take quite a while to reach maturity.

While it may start consistently doubling after each feed relatively early (generally from around 14 days old) it still has lots of growing to do.

It will take a lot more time (and feeding) to develop its flavour and peak strength. I recommend not storing your starter in the fridge until it's reached maturity.

So once your starter has reached maturity, each time you use your starter in making sourdough bread, it is considered "discarding" in that you use it and can then just feed what's left in the jar for your next batch.

It's easier to explain using an example.

Say you have 120g of starter in your jar. You use 100g in your sourdough bread and return 20g of starter to the fridge until you want to feed it again to make more bread.

It's already been fed so you could just put it back into the fridge and then feed it again when you are ready to make your next lot of sourdough bread.

If you are keeping your sourdough starter on the counter, you could leave it for a few hours and then you'd need to feed it again ready to make your next batch.

Whether you use your starter in your bread making or you discard your starter in other ways - you MUST discard to keep your starter healthy and thriving.

You might also enjoy this comparison of sourdough discard vs sourdough starter (are they really that different?).

2 Comments

Sheila says:

March 31, 2023 at 7:47 am

GREAT tips!!!

Hannah Walters says:

September 3, 2024 at 7:41 pm

Thank you!
You are the first person I have seen say that ‘using’ = discarding (most recipes add quantities of flour/water and then have to chuck half the starter each time 😟)
I have made sourdough (and old dough) breads for decades. The starter sleeps in the fridge in a small jam jar, I give it a spoon or two of flour (plus water if too thick) and put it by the Aga to wake it up. Once it’s bubbly about 3/4 if the jar goes in a basin with a cup of flour and left to make a ‘sponge starter’ and the remaining starter in the jar gets another couple of spoons of flour and water, left a wee while to get feeding, then goes back to the fridge for a nap - not a bad life 😊
Periodically I swap it into a clean jar (rinsing every scrap of the residue into my dough!)
Making a sponge puts a much greater ‘living’ volume through the dough, so that tends to take off a bit faster too. I find these stages, because sourdough is so forgiving of lax timekeeping, fit easily around work/going out/sleeping etc. - though it is extraordinarily difficult to persuade others that just because it happens over a longer period of time doesn’t mean it’s time consuming!
I also recently read (and can confirm) that it doesn’t need the traditional long knead - if you just give the dough a couple of folds every time you pass the basin it basically kneads itself by re-rising. A useful tip from a professional baker who had been on the point of giving up because of arthritic hands!