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How to Tell If Sourdough Bread Has Gone Bad

Look for these signs of spoilage. If you’re still unsure, toss the bread out for safety reasons.

Whether you are an avid sourdough baker, a beginner in the world of sourdough, or you just like buying sourdough at your local grocery store, you need to know when sourdough bread has gone bad.

(Considering that sourdough smells sour and tastes tangy to begin with, this can be a surprisingly tricky thing to do.)

There is nothing so disappointing as picking up what appears to be good sourdough bread and finding that it has become inedible. To prevent this, familiarize yourself with the longevity of sourdough bread and the tell-tale signs that it has gone bad.

Although we will go into more detail below, you can generally tell if sourdough bread has gone bad by three signs, all of which are subtle but hard to ignore: it’s moldy, it smells off, and/or it tastes bad.

Learning to recognize these signs will not only help you keep food waste to a minimum—something we should all strive to do—but save you from a major upset stomach or, worse, food poisoning.

Signs Your Sourdough Bread Has Gone Bad

Sign #1. Molding on and/or beneath the surface

Moldy sourdough bread is unsafe to eat, and cutting away the moldy pieces doesn’t make it any safer. If your sourdough bread has become moldy, it’s best to throw it away so that no one in your household makes the mistake of eating it.

A loaf of sourdough bread will usually keep for 4-7 days (on the low end if stored in a plastic bag, and on the high end if stored in a bread bag made out of cotton).

During this time, mold spores from the air land on the bread and slowly but surely begin to multiply until the mold forms a colony visible to the naked eye. Since bread is porous, that mold can easily colonize it well below the surface.

That mold on your bread is different from the mold on green cheese. The latter is considered safe for human consumption, whereas the former—and the toxins that it produces in your food—can get you hospitalized.

As a matter of fact, the Centers for Disease Control and Prevention estimate that 48 million Americans contract food poisoning every year. Roughly 128,000 of them get hospitalized, and 3,000 die.

It almost goes without saying that you don’t want to be anywhere near those statistics.

Sign #2. An off, almost medicinal odor

Another sign that the sourdough has become bad is that it will have an off odor.

To understand when sourdough smells bad, you should first know what sourdough smells like when it is fresh out of the oven. Normally, sourdough bread has a yeasty and slightly sour smell.

When sourdough bread starts to go bad, its smell changes from sour and yeasty to musty and medicinal. If you give that loaf of bread a whiff and it causes you to raise eyebrows, err on the side of caution and throw it away.

Something for you to keep in mind as you’re giving that sourdough bread a whiff: Since mold can grow under the crust of a loaf of bread, the musty, almost medicinal smell can be present even if you don’t see the mold on the surface.

When the bread smells off, but there’s no mold on the crust, that doesn’t mean it’s safe for you to eat.

Sign #3. A bad taste that makes you cringe

For safety reasons, you should only taste-taste loaves of sourdough bread after you’ve checked that, first, they are not moldy on the outside or inside and, second, they don’t smell musty and medicinal.

When the taste of bread makes you cringe, that bread has obviously spoiled. Spit it out immediately, brush your teeth and rinse your mouth with mouthwash to get rid of the nasty taste, and throw the loaf in the bin.

At this stage, there’s no way you wouldn’t be able to tell. Spoiled sourdough bread tastes nothing like freshly-baked sourdough bread. Instead of sweet and sour, it’s bitter and overwhelmingly herby—but in a bad way.

There’s a reason for that. Your tastebuds are as much a source of pleasure as they are a defense for your body. Nine times out of ten, when something doesn’t taste good (not in a way that doesn’t appeal to your preferences but in a way that makes your body want to react), you shouldn’t eat it.

Stale vs. Spoiled Sourdough Bread

Unlike spoiled sourdough bread, which has no place in your stomach, stale sourdough bread is dried out and, with a little creativity, can be salvaged.

Staling occurs when the starch molecules in bread dry out and go back into a crystalline state. This dries out the bread and makes it hard in a process that professional bakers and food scientists call “starch retrogradation.”

When the bread is baked, the starch molecules swell because they absorb water, changing the crystalline state of the molecules to a gelatinized state. This, as you can imagine, makes the bread softer.

However, as soon as the loaves come out of the oven, the water molecules begin to dissolve, and leave the starch molecules. This causes the molecules to return to the crystalline state and, as far as texture is concerned, stiffen.

How To Salvage Stale Bread

Just because your bread is a little stale does not mean you have to throw it out immediately. 

Take the stale loaf, sprinkle it with some water, and bake it in a 300°F oven for 10 minutes. The result is a pretty decent, if chewy, leftover loaf. Be sure to preheat the oven for at least 10-15 minutes. While the bread won’t taste as great as a fresh loaf, it will soften and rehydrate.

Or make one of my favorite stale-bread recipes, the Italian-peasant-cooking staple Pappa al Pomodoro, with it. All you need is a bit of olive oil, a few cloves of garlic, a can of peeled tomatoes, and a pinch or two of sea salt. 

How To Store Sourdough Bread

Baked bread and Pappa al Pomodoro taste great and all, no doubt about it, but you probably want to know what you should be doing to keep your sourdough bread from becoming stale in the first place. We explain below.

The best way to store sourdough bread is in a bread bag at room temperature. Made of cotton or linen, this type of bag lets the bread breathe, so it doesn’t spoil as fast, and it comes out crunchier than when wrapped in plastic.

Wrapping the bread in a plastic bag and throwing it in the bread box is always an option. However, it invites moisture—promoting mold growth—and softens the crust of the bread almost immediately. So, while that’s exactly how many home cooks store their bread, plastic bags are not necessarily the best option.

Freezing Sourdough Bread

Suppose you made a lot of sourdough bread and, now, you don’t know what to do with it. Refrigerating it isn’t an option, but storing it in the freezer for a good few months is.

Allow the bread to cool down before slicing it to prevent excessive moisture loss. When you slice a piece of hot bread, the moisture will immediately leave at a higher rate, and it can cause the bread to become stale quicker. 

If you want to freeze your sourdough bread:

Wrap the bread up in a freezer bag. Frozen food is safe to eat indefinitely, but sourdough bread should keep its best aroma and flavor for 3-4 months;

When it comes to deforesting the sourdough, do not let the bread thaw, as it can promote staling. Just preheat the oven to 300°F and bake the bread for 10-15 minutes, getting rid of the excess moisture.

Defrosted sourdough bread will not taste as nice as fresh bread, but it can be a great way to preserve food instead of promoting food waste. 


When bread goes stale, you can be creative and make a couple of different dishes with it, which is also great for reducing food waste. Make sure to store the bread properly to slow down the staling and molding processes in the first place.

That said, sourdough bread doesn’t last forever. If your sourdough bread has visible signs of mold, it has gone bad and is inedible. If the bread also smells musty and medicinal and/or has an unpleasant taste when you bite into it, DO NOT eat it.

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Written by

Jim is the former editor of Home Cook World. He is a career food writer who's been cooking and baking at home ever since he could see over the counter and put a chair by the stove.