🥧🎉 LIVE online class: Let's make choux pastry & Discuss Science. Oct-22nd, sign up here 🎉🥧
If I had to choose only one type of food I’d be allowed to eat for the rest of my life, freshly baked bread would rank high on my list of contenders. The smell, whether it comes from a hot home oven or a bakery, has the power to make me hungry. The stark contrast between a crusty crust and soft inside is delicious. A good, freshly baked, bread doesn’t need much else to become a great meal, maybe some butter, or cheese, or just a few fresh tomatoes.
Unfortunately, bread doesn’t stay fresh for long. The deterioration process will literally start as soon as the bread is out of the oven (or off the heat source). Within a few hours (in the case of a traditional French baguette) or days (sourdough breads), your bread will have turned stale. You can still eat it, if there’s no mold on it, but it’ll be tough and dry. Gone is that crunchy crust and moist inside. Instead, you’ll need to chew your bread extensively, and literally tear it apart.
Preventing, delaying, or even reversing this process is a holy grail of many bread makers and eaters. Luckily, we’re not completely without tools. There are ways to slow it down (don’t store your bread in the fridge!) or reverse it. Once you know what causes staling, you’ll have no problem keeping your bread good just a little longer.
What makes fresh bread so great?
Of course, before a bread turns stale, it’s fresh. Let’s have a look at what makes fresh bread so great first.
A simple loaf of bread is made of at least wheat flour, water, yeast, and probably some salt. The dough you make will be soft and flexible, easy to deform, knead and shape into your desired bread. Once it’s baking, it transforms into a light and airy ‘sponge’ that holds its shape. The heat of the oven causes the proteins to denature, the starches gelatinize, more on that later.
What’s more, the water in the bread will be redistributed. Whereas water is spread evenly throughout the dough, that is no longer the case in a baked bread. The crust contains considerably less water than the center, giving it that crunch.
Flavor and smells
Accompanying all those changes in texture and structure is a change in flavor. While bread is in the oven, sugars and proteins react with one another in the Maillard reaction. This complex set of chemical reactions causes the bread to turn brown and causes the formation of all sorts of aromas and flavors. When your bread comes out of the oven the high temperatures causes a lot of these to evaporate and get into the air, hitting your nose when you enter that bakery or open that oven door.
A few minutes after you’ve gotten your bread out of the oven, the difference in moisture between the crust and center is at its maximum, from hereon onwards, moisture will move into the crust again.
What happens when bread turns stale
When your bread is just out of the oven and has cooled down, it’s at the top of its freshness. Staling sets in very soon after. During staling bread loses its freshness, it loses that crunchy crust and the center turns dry and chewy. A truly stale bread requires a lot of chewing and teeth power to be eaten. Stale bread hasn’t spoiled though! It’s still perfectly fine to eat, just not as delicious.
In order for bread to turn stale, two main mechanisms are at play: moisture movement & starch retrogradation.
1. Moisture moves into the crust
Water in most foods has a very strong tendency to move throughout. Energetically, it is best for the water to be distributed evenly, such that the water activity is the same throughout the whole food. This doesn’t just happen in bread, it happens in pies (which is why the crust loses its crunch after a while), creme brulees and many more foods.
In the case of bread the crust is a lot drier (and has a lower water activity) than the center of the bread. As such, almost immediately after the bread has cooled down, moisture from the center will move into the crust. What’s more, if you live in a humid environment, it’s likely that moisture from the air will seep into the crust as well. In a worst case, eliminating all that crunch in a matter of a few hours!
Keep in mind that for all of this to happen only a small amount of water needs to actually move. Research has shown that probably only about 3% of the water in bread actually moves around significantly to cause the crust to soften and the center to be less moist.
2. The role of starch
Even though moisture has a clear role to role, it only partially explains why bread turns stale and turns dry! As it is, the main reason for bread turning stale doesn’t have to do with bread drying out. Instead, it is because of a molecular reconfiguration of the starch in bread.
Starch is a main component of wheat flour as it is for many other major food sources worldwide such as potatoes, rice, and cassava for instance. It is a carbohydrate and is made up of two types of molecules: amylose & amylopectin. Amylose is a relatively simple molecule, it is a long chain of glucose units. Amylopectin is also made from glucose, but instead of it being a linear chain, it has a more complex branched structure. Every crop contains a slightly different ratio of these two molecules, causing the starch to behave slightly differently.
Within flour the starch is present in the form of granules. When dispersed into water, these granules absorb moisture (think of mixing flour with water). Once you heat up these granules they will start swelling up and absorb some more moisture. Whereas previously they were crystalline, they lose some of this crystallinity, meaning they become more unordered in structure. No need to understand the details, but it is important to know it happens in order to understand staling. At some point, the granules break, releasing mostly amylose into the rest of the dough. This whole process is called gelatinization. If you’ve ever made a roux, to thicken a sauce (e.g. a bechamel), you’ve seen gelatinizing at work!
Sign up to our weekly newsletter to be updated on new food science articles.
Once gelatinization has occurred it is irreversible. You won’t be able to get back to your original starch granules. Or, better said, you won’t be able to transform that bread back into a dough, even if you’d add back the water it might have lost!
Freshly gelatinized starch is delicious, think of a freshly baked bread, freshly cooked rice or a just baked potato. However, over time, the starch changes again, which causes your bread to turn stale, the potato to become chewy and dry and the rice to be firmer. It’s called: retrogradation.
During the staling of bread, starch again changes it configuration. Whereas it cannot go back into those original granules, the molecules can organize themselves in a slightly more structured way within the bread. The amylose and amylopectin molecules can reorient themselves within the bread and form structures. The starch becomes more ordered and as such more crystalline. This is the main reason of bread turning dry and stale!
Amylose and amylopectin both retrograde slightly differently. The retrogradation of amylose sets in more quickly than that of amylopectin and is less reversible than than of amylopectin as well. Luckily, some of these structures can be reversed by heat, which opens up some ways to revamp your stale bread.
Staling vs. Spoiling
A quick note, as we mentioned above, bread turning stale is just a quality issue, it does not impact the safety of your bread. If you store bread outside of plastic in a non-humid room temperature environment, most breads turn stale, very stale, well before they ever spoil because of the growth of microorganisms. However, if you don’t store your bread properly, it is possible for moulds to grow on your bread. We’ve written more about that here.
How to prevent/slow down staling of bread
Just about every bread will stale over time, if you leave it enough time. There are several ways to significantly slow down the process though.
Do NOT store bread in the fridge
First of all, do not store a freshly baked bread in the fridge. Whereas storing bread in the fridge slows down growth of micro organisms, it actually speeds up the starch retrogradation process. In other words, it speeds up staling of bread.
If you’re worried about it staling and spoiling: store bread in the freezer. A freshly baked bread that’s frozen will come out almost identical to how it was frozen and you can easily store it for months.
A commonly used method to prevent staling is by partially breaking down those complex starch molecules. If they can’t form those organized crystalline structures, it won’t turn dry. You can break up starch molecules using specialized enzymes: amylases. Amylases are broken down in the oven by the heat, so they’ll do their work within the dough, cutting up the starch molecules just enough to prevent that retrogradation later on.
Amylases aren’t just added to prevent staling, as we’ve discussed elsewhere.
It is also well documented that sourdough breads can be kept several days longer without them turning stale and becoming inedible! It is thought that the bacteria in the sourdough have a similar mode of action as the enzymes discussed above. They break up some of the starch (and even protein) molecules, decreasing the extent of staling. Since every type of bacteria is slightly different, different sourdoughs will have a different impact. It’s quite complex actually!
You might have also noticed that an enriched bread with more fat takes a little longer to turn stale than a ‘regular’ simple bread without any fat. Fat can slow down retrogradation by sitting in between all those starch molecules, preventing them from forming that more crystalline structure.
How to reverse the staling process
Despite all your efforts, your bread might still turn stale. But hope is not yet lost! There are a lot of ways to still use this bread. Most of these methods will use some sort of heating process to revamp your bread since heat can reverse starch retrogradation almost completely.
Bake it in the oven
If your (unsliced) loaf has turned stale, all you need to do it reheat it. Most loaves need 5-10 minutes in the oven at 180C/375F to be fresh again. Do keep in mind that reheating your loaf can make the crust thicker (which some might consider a benefit) and that the required time strongly depends on the size of your loaf.
Also, this method isn’t very suitable to slices of bread (use a toaster for those) or flatbreads! The oven will simply dry them out.
Heat in the microwave
For soft flatbreads especially (such as tortillas, chapatis, naan) re-heating in the oven won’t work. The oven will dry out that bread, making it crunchy and hard. Instead, you had best turn to the microwave for help! A microwave heats food by heating up all the water molecules. It doesn’t crisp up food but heats them up from the inside.
Take your day-old naan or pita and reheat it in the microwave for 10-20 seconds (exact time depends on your microwave settings). The microwave will reverse the starch crystallization processes without drying out the bread. You naan will be soft and warm!
Use it in another dish
In some cases you don’t need to fully reverse staling, you just want to make it soft enough to eat again. In those cases using the stale bread in a dish that requires heating and maybe adds some extra liquid is a great solution. French toast is perfect for this. The combination of heat and soaking in some liquid makes it a great vehicle for stale bread.
Luckily, a lot of the breads we bake or buy are eaten (or frozen) well before they have time to get stale. Because in the end, a freshly baked bread too delicious to pass by.
Classo Innovation, Alles over de kwaliteit van brood, link
Hug-Iten, Susanna, Staling of bread and bread model systems – role of starch and amylases, 2000, PhD-thesis, link
Hug-Iten, S. & Escher, F. & Conde-Petit, Beatrice. (2003). Staling of Bread: Role of Amylose and Amylopectin and Influence of Starch-Degrading Enzymes. Cereal Chemistry – CEREAL CHEM. 80. 654-661. 10.1094/CCHEM.2003.80.6.654., link
Taylor, Steve, Advances in Food and Nutrition Research. Netherlands, Elsevier Science, 2005. p.146, link