How bread goes stale – Science & Tricks

One of my favorite foods by far is freshly baked bread. Unfortunately, bread doesn’t stay fresh for a long time. As soon as it comes out of the oven, the ageing process sets in. It starts getting old as soon as it comes out of the oven.

Preventing ageing of bread is probably a holy grail of the bread industry. A bread that doesn’t get stale over time would be their ideal. And when baking your own bread (or storing it) you’ll also want to try and keep it good for as long as possible (or find ways to use old bread).

But how does bread turn stale? And why? And is there anything you can do about it?

What happens when baking bread?

Before we can discuss what happens when bread turns stale, we’ll have to look into what happens when bread is being baked. Dough is transferred into bread during the baking process in the oven. As discussed in the post on the bread making process several things happen in the oven:

  • Water evaporates from the bread, the crust will dry out more than the inner crumb
  • Gases (mostly carbon dioxide) expand
  • The gluten networks forms and stabilizes
  • Starch gelatinizes

The role of starch

When bread turns stale various processes occur. However, probably the most important one has to do with starch. In order to understand this in some more detail we’ll zoom in on what starch does and is.

Starch is a carbohydrate and is made up of two components: amylose & amylopectin. Amylose is a relatively simple molecule, it is a long chain of glucose units. Amylopectin is slightly more complex, it forms a more branches structure (think of a tree).

In flour starch forms granules in which amylose and amylopection sit. Every flour has a slightly different composition of its starch since it’s due to the growing conditions and genetic factors.

Starch will gelatinize during baking (as we also discussed for thicking of pie fillings or bechamel sauce). This is an irreversible process where several things happen. The granules swell by taking up water, they lose some of their crystallinity (which is important for understanding staling) and granules can break, causing mostly amylose to leak out.

Staling of bread

During staling of bread various processes occur that cuase the bread to turn stale. The first is the movement of water.

Since the center of the bread is moist and contains more moisture than the crust, moisture will travel from the center to the crust. Moisture will always try to do this (just like it does in crusty pies with a creamy filling). This causes a soggy instead of fresh crusty crust and will cause the center to dry out slightly.

However, this drying out of the center is not the sole cause of the stale bread. It has been found that probably only 3% of the water gets redistributed in stale bread.

Starch retrogradation

The main process that has occurred when your bread has turned stale, which is also why we had to spend some time on discussing starch.

As we discussed, during baking starch loses some of its crystallinity. Crystalline structures are also very ordered structures of molecules. However, during baking these structures become less ordered and more random. After baking these structures change again in a process called retrogradation.

Retrogradation of starch consists of two processes: gelling and crystallization. Amylose is the fastest here. It will form a gel quite quick (probably already during cooling of the bread). Over time the gel can become more stable due to cross links and crystallization of the molecules. These gels are pretty stable and cannot be reversed by heat (require >150°C).

Amylopectin on the other hand crystallizes more slowly. It will also form a more structured gel than was present in a freshly baked bread. However, a temperature as low as 60ºC can already undo this.

pumpkin bread
Starch retrogradation not only occurs in breads, it is also a reason pumpkin bread (and other cakes) turn dry and stale over time. This does take longer and in these causes spoilage by micro organisms might be faster than the staling process.

Reversing staling of bread – freshening things up!

Staling of bread can be reversed partly. As we discussed above, some of the transformations are stable for increased temperatures, but some can be reversed by heating the bread back up.

If you happen to have an old loaf lying around, just put it back in the oven (180C for 10 minutes should do the job but it’s slightly bread dependent). However, do not do this once the bread has been sliced. Once the bread is sliced it will mainly lose water in the oven if you reheat it and thus turn dry and crispy.

Slowing down the staling process

Do not store your bread in the fridge (although I’ve read that bread with enough preservatives, that simply don’t get stale even after more than 7 days can be stored in the fridge, but well, I generally do not really like those breads even when fresh)! Storing bread in the fridge might slow down microbial spoilage of your bread, it really does not help the quality of the bread. The staling process actually goes faster in the fridge than when it’s stored at room temperature.

Want to keep your bread fresh for longest? Store it in the freezer, the staling process is just about stopped completely in the fridge. Once thawed the bread will still have a crusty crust and soft fluffy inside.

Preventing staling

There are also ways to prevent staling of bread and of course the bread industry has looked into this.

One method is to add an enzyme called amylase. This enzyme will cut up the starch molecules into smaller ones and this delays staling. It seems to work by preventing crystallization of the molecules.

Another method is to add more fat. Fat will sit in between the strach granules and can slow down the formation of these more complex gel and crystalline structures.

Last but not least I’ve read that adding sugar (will ‘bind’ water) and allowing for longer fermentation (thus proofing of the bread) will delay staling of bread. Not 100% sure how or if those work and from which concentrations/durations. If I would have to add 10% sugar I probably wouldn’t like the taste of the bread as much any more.

Sources

In 2000 a very extensive PhD thesis has been written on staling of bread and how to prevent this using various amylases. A lot of my post has been based on this research.

A 2003 research article also looked into the effect of amylase on the staling process.

Another far more in-depth article on the topic that I used for fact checking.

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