Why Sourdough Bread Lasts Longer And Doesn’t Mold

Have you ever noticed how homemade white bread will go stale and moldy quickly, but sourdough bread seems to last forever without going bad? I’ve done some research to find out what is happening to sourdough as it ages.

Sourdough bread lasts longer because of higher acidity, and the lactobacillus bacteria producing natural antifungal compounds. It also has longer before it will go stale because a long fermentation process slows the rate of hardening and moisture loss.

I’ve got some explanations of why this happens next, and also some tips on storing bread to make it last the longest.

Why Sourdough Bread Lasts Longer

The keeping qualities of bread can be boiled down to two things: going moldy and going stale.

1. Why Sourdough Doesn’t Mold As Fast

Sourdough can still get moldy, but it is a lot slower to mold than yeasted homemade bread because of the extra microbes.

Many people will know that sourdough is acidic from its sour taste. We’ve got acetic acid which gives us a vinegary taste, and lactic acid which gives us the milky sour cream-type flavors.

Research has found that acetic acid is effective at preventing mold growth on fruit. So that is no doubt playing a part here. To read more about the acids at work in sourdough, check out my article on what makes sourdough sour.

Secondly, there is a study that directly investigated the antifungal properties of sourdough. It found that the lactobacillus bacteria which is found in sourdough actually produces antifungal compounds when it digests the flour.

Sciencedaily.com writes that the bacteria ‘produced substantial quantities of hydroxylated monounsaturated fatty acids which the researchers found strongly inhibited mold formation.’

So sourdough creates its own natural preservatives while fermenting!

2. Why Sourdough Doesn’t Go Stale As Fast

I initially thought bread going stale and bread drying out were the same thing, but they are not. While drying is part of “going stale”, there is more going on here.

It is down to more chemistry, this time recrystallization of starch molecules. Basically, these molecules are regrouping and start to harden as soon as they come out of the oven. This leads us away from the soft, squishy bread that we like.

Long fermentation results in delaying this process from the build-up of lactic acid bacteria and natural yeasts. And because sourdough is a slow fermenting dough, we often see that the bread will firm and stale slower.

Dough that has fermented longer also has the chance to absorb more water, which means it has longer to dry out later.

How Long Sourdough Bread Can Last

Sourdough bread will last 5-6 days before it goes too stale. It will take another 1-6 days before it goes moldy.

As we mentioned before, there are a few chemical reactions that are taking place which leads the bread to deteriorate. It depends on the culture that has built up in your starter that will determine the keeping qualities.

Other factors are the temperature and the moisture, so keeping these down will help.

One study with a French strain of sourdough bacteria found that the sliced bread didn’t mold for 12 days. This is seen to be a few days longer than the typical period perhaps because it was a less common type of bacteria.

How to know if sourdough has gone bad

Sourdough will first go stale from the crumb hardening and drying out. It will then show signs of fungus in the form of visible mold on the surface.

Staling is the first main culprit to watch out for as the antifungal properties will keep the bread from going green for quite a while. If the bread looks fine to eat but is a little hard, you can always toast it which makes it much more pleasant.

Which Bread Lasts The Longest

  • Yeasted bread- 2-3 days
  • Bread with pre-ferment – 3-4 days
  • Sourdough – 5-6 days

Straight yeasted dough will last the shortest and sourdough will last the longest. Dough that has had a pre-ferment, such as poolish or biga, will extend the life of yeasted dough by a day or two.

If we take a spectrum of bread that goes from straight yeasted dough to dough made with a sourdough culture, we can spot a pattern.

Breads that have had more time to ferment will last longer, it’s as simple as that.

The process literally creates natural preservatives which is an amazing benefit of sourdough. Much better than bread which has unnatural preservatives added I am sure you will agree.

I wrote about how this extra fermentation boosts flavor and texture in improving bland homemade bread.

How To Keep Sourdough Bread Crusty

Bread can be kept crusty by storing it uncovered for the first 24 hours, and then moving to a breathable container such as a linen bag. This avoids the crust becoming soft. After this, the slices can be lightly toasted to bring back the crisp crust.

There is no beating a crisp crust, but it won’t last forever. Bread is definitely best eaten fresh and just cooled. This will be 2 to 6 hours after removing from the oven.

The crust will then remain good for about one day. Leave it cut side down to protect the interior from drying.

After this, it’s a tradeoff between the bread going stale and keeping the crust crisp. If you place it into an airtight container then the bread stays moist for longer, but this moisture travels to the crust and makes it chewy.

A cloth or paper bag is a good storage option. You can buy a reusable linen bread bag online. This lets the air circulate and have a balance between drying out and maintaining the crust.

After day 3 you will have to toast the bread to bring back the crust. A light sprinkle of water before toasting rejuvenates it well, but it won’t last for too long as it will harden quickly.

How do you keep sourdough bread from getting hard? This is difficult to stop because it will naturally stale. If you prefer a soft chewy crust, then you can place it in an airtight container once it has cooled down.

How To Store Sourdough Properly

Here is how I store my sourdough which I think gets the best of the bread once it’s out of the oven:

  • Store uncovered day 1. Enjoy the crust which remains good for the first day and place the cut side down to stop the crumb from drying out.
  • Store in a breathable bag on days 2-3. This gives you a balance of a nice crust and prevents it from staling too much. A linen bread bag or kitchen towel works well.
  • Store in an airtight container on days 4-5. Now you need to store it in a breadbox or airtight container. It will become soft but will prevent it from becoming too hard.
  • If you’ve still got bread left, you can tear it up and make croutons and breadcrumbs or you can slice and put in the freezer. See my post what to do with failed bread for more ideas.

Follow these tips which should also help to keep the bread at its best:

  • Do not refrigerate it. The fridge is a dry environment and will cause it to go stale faster than leaving it outside.
  • Do not slice warm bread. As tempting as it is, the crumb will set once it has fully cooled which makes much better slices. About 2 hours is the best – I know it’s hard to wait!
  • Don’t put it straight into an airtight container. Bread can “sweat” in an airtight container. Warmth and moisture = bad for bread.
  • Store in a cool place. The heat will promote bad microbes to grow and spoil your bread. A cool place out of sunlight is best.


I hope I answered all your questions regarding does sourdough last longer. It was interesting to find some real scientific studies into the natural preserving qualities that sourdough has – what a superfood!

Sourdough not only tastes great but is better for you, and lasts longer than a bread made with commercial yeast. It’s a really great benefit that the keeping qualities improve with sourdough – a reward for the hard effort that went into making it.

Tom Hambly

Tom Hambly is the founder of Crust Kingdom. As a self-taught cook, he has been perfecting making pizzas at home for over a decade. Now he runs this site to help millions of people make pizza every year. About Tom Hambly.

One thought on “Why Sourdough Bread Lasts Longer And Doesn’t Mold

  1. Sorry but… I cool, slice and freeze. I do my share of toast, but I make my wife sandwiches she LOVES with bread I gently thaw in microwave. You DO NOT only have 5-6 days to enjoy the bread you created. That’s ridiculous.

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent Posts