There’s nothing like eating the bread on its first day when it’s fresh, chewy, and full of flavour.
What happens though in the coming days, when bread becomes gradually stale and firm?
Recently, I’ve found a small piece of bread from the week before that I had forgotten to eat. Luckily, it’s sourdough bread and it hadn’t developed any mold whatsoever. However, it was impossible to cut through and eat it. It had become very hard, almost like a stone.
If I had been in the same situation some years ago, most probably I would have discarded it. At that moment though, I just warmed it up shortly in the microwave and got it back perfectly soft. It had regained much of its initial freshness.
But why’s that, what had happened in the microwave and a bread so hard and firm became again soft and edible?
To answer this, we need to understand why bread hardens in the first place after it has cooled down and kept stored for a few or several days. In the past, the common belief was that bead staling and hardening is a result of water loss due to evaporation. This makes sense and still stands as a cause but even if you store your bread hermetically closed so as to prevent water loss, you will still find it harder after some time. Science evolved and showed that the main cause of bread staling is a chemical transformation that occurs to starch, known as retrogradation.
To explain better starch retrogradation, let’s go one step backward to see what happens to bread, in this case to starch, during baking.
Starch gelatinization
The long molecules of starch are organised into granules, which are embedded into the gluten structure. To get a better idea of how starch granules look like per se, I tool pure corn starch and mixed it with some water.
I used my paper microscope (foldscope) to look at it.
The next microscopy images show the typical, polyhedral in shape granules of corn starch.
When starchy foods are heated up in presence of water and the temperature raises to more than 60 ºC, starch granules absorb water, which penetrates in between the starch molecules, disrupting the chemical bonds that were keeping the latter connected each other and closely packed. Water keeps the starch chains apart by forming its own bonds with them. As a result of this, starch granules increase in volume and swell like balloons that at some point due to excessive force disrupt and spit out some starch molecules into the medium. The whole process is known as starch gelation or gelatinization because starch-water bonding creates a gel-like consistency.
Gelatinization is a very important process during cooking, being the main event that transforms a raw starchy food into a soft and edible one.
To observe starch gelatinization, I took the corn starch-water suspension from before and heated it up in the microwave.
As you can see in the following image starch granules look indeed bigger and more translucent than before, reflecting thus their gelated state.
Starch retrogradation
Now, let’s go back to bread and see what occurs to it after it had gelated in the oven. When baking finishes and it’s let to cool down, starch starts to experience the reverse process, which is retrogradation. As soon as the bread temperature drops under gelatinization level the water molecules are not capable any longer to bind starch and are gradually pushed away from starch molecules, which are coming back closer to each other, forming again chemical bonds. Subsequently, starch loses its gelly consistency and it starts gradually to set.
This is something that initially we very much want to happen so as to enjoy eating bread with a soft and chewy crumb and not a gummy, wet, and hot mash. That’s why, no matter how much we’re looking forward, we should resist cutting bread that just came out of the oven. No matter the amazing and inviting smell, we should rather wait for a couple of hours until internal temperature drops and starch sets.
Unfortunately, starch retrogradation goes on even after the bread had cooled down and because of that bread will inevitably lose its freshness and become crumblier and harder over time.
However, if you reheat the bread that had become hard, the starch will rebond with water and gelatinization will occur again. The bread will become soft and regain a good amount of its initial softness. You will be able to eat it pleasantly again.
But keep in mind that when it will cool down for a second time, retrogradation will take place again, this time much faster than before.
So, if your bread is hard, just warm it up and eat it quickly!
Bread storage tips
- Starch retrogrades faster at lower temperatures. Because of that, you should never store bread in the fridge.
- However, when bread is frozen retrogradation is not an issue. Therefore, for long-term storage, the best way to store bread is to put it in a plastic bag and freeze it. When you want to eat it again, you let it for some hours at room temperature to thaw and it will be almost as fresh as it was before.