How Do You Know When Sourdough Bread Has Gone Bad?

Sourdough bread can go bad in two ways; it can get moldy and it can turn stale. Moldy sourdough bread is unsafe to eat and should be discarded, while stale sourdough bread can be saved by reheating the bread to 90 Celcius.

First look, then feel your bread; look out for any signs of mold while feeling the bread to check if it has hardened up from becoming stale. It is best not to smell your sourdough bread if you are unsure if it has gone bad as you may inhale some of the moldy spores.

Mold takes on many texture and colors depending on the temperature, humidity, the type of bread, and how long the mold has been left to grow; if you see fuzzy growth of any color on your sourdough bread, it has most likely gone moldy, it can not be saved and you should discard the bread.

As sourdough bread stales, it gets progressively stiffer and harder in texture.

What happens when bread goes stale?

The process of staling is called starch retrogradation, where starch molecules in the sourdough bread bread dries out and reverts back into a hard crystalline state. A tell tale sign of sourdough bread that has gone stale is a dry and hard crumb.

Prior to baking, starch molecules is devoid of water and exists in a hard crystalline state. During baking, the starch molecules absorbs water and swells up, changing from the hard crystaline state to a soft gelatinized state.

As the bread leaves the hot oven and begins to cool, water molecules start to dissipate out of the starch molecules, reverting it back to its hard crystaline structure; the sourdough bread progressively gets drier and harder over time.

How long before sourdough bread goes stale?

Homemade sourdough bread stored at 25 Celcius in a sealed box or wrapped in foil will last 4-5 days. Store bought bread may sometimes contain preservatives and will last 5-7 days.

Sourdough bread stored in the open, dries out quicker due to excessive air flow around the bread, and therefore goes stale quicker as well. A warmer environment also causes the loaf to dry out faster, as rate of evaporation increases with temperature, which accelerates the staling process.

When purchasing sourdough bread, check the label for the common bread preservatives: calcium propionate, sodium benzoate, potassium sorbate and sorbic acid, if you want your sourdough bread to last longer.

How to revive stale sourdough bread?

Take your stale loaf and put it quickly under running water to only wet the outside. Then, preheat the oven to 150 Celcius, and bake the wet loaf for about 10 minutes, or until the internal temperature of the loaf reaches 90 Celcius. The loaf will be rehydrated, soften and be good as new. 

As we reheat the wet loaf to 90 Celcius, we are reversing the process of staling by allowing water to be reabsorbed by the starch molecules, causing it to change from its hard crystalline state to a gelatinized state; the loaf is now back to the same form as a freshly baked loaf.

Remember that a stale bread has gone through starch retrogradation where the starch molecules dry out during cooling, and hardens as it reverts back into a crystalline state.

Stale sourdough bread that has been revived should be consumed immediately, as it will turn stale much faster once it cools down.

How to prolong the shelf life of sourdough bread?

We can prolong the shelf life of our sourdough bread by delaying staling and molding of our sourdough bread. Store your sourdough bread in a sealed container to prevent the bread from drying out and going stale, preferably in a cool and dry environment to discourage mold from growing.

  • Wait for your freshly baked sourdough bread to completely cool before storing it in a airtight container to prevent moisture from accumulating and promoting mold growth.
  • Ensure your freshly baked sourdough bread has completely cooled before slicing it, to prevent excessive moisture loss from cutting open a hot loaf, which hastens the staling of the bread.
  • Do not refrigerate your sourdough bread as the bread goes stale at the quickest rate between 0 – 10 Celcius, hence refrigerating your sourdough bread will cause it to stale much faster than if you store it at room temperature.
  • To keep your sourdough bread fresh for up to 3 months, wrap the loaf tightly with plastic wrap, and freeze to -18 Celcius, which will prevent the bread from getting moldy and stale; the bread’s quality will start to decline after 3 months of freezing.

Frozen sourdough bread will never taste as good as freshly baked sourdough bread as the bread has to go through the staling danger zone of 0 – 10 Celcius twice; once when the bread is freezing, and once when the bread is thawing.

How do you defrost frozen sourdough bread?

Preheat the oven to 160 Celcius, and load the frozen bread into the oven directly from the freezer. Bake for 20-30 minutes or until the internal temperature of the loaf reaches 90 Celcius.

Do not wait for the bread to thaw before loading it into the oven, as the extra thawing time will cause the bread to stale further. The frozen bread will not burn in the oven as the bread is baked as a relatively low temperature of 150 Celcius.

What can you use stale sourdough bread for?

  1. Breadcrumbs – toast your 1/2 inch slices of stale sourdough bread in a preheated oven of 200 Celcius for 15 minutes. Allow it to cool completely before blending them in a mixer into a coarse powder.
  1. Croutons – dice your stale sourdough bread into 1 inch cubes, drizzle generously with oil or butter and season with salt and pepper. Spread the diced cubes onto a baking tray evenly, and bake in a preheated oven of 200 Celcius for 10 minutes or until they have reached your desired level of crispiness.


Hey there! I'm Sam, your go-to pal for all things sourdough. I've been baking and kneading for 10 fun-filled years, and I can't wait to share the joy of turning simple ingredients into heavenly sourdough bread with you. Grab your apron and let's dive into this amazing world of sourdough bread together on this blog.

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