Curious Cook: Why bread goes stale and how you can unstale it

Curious Cook: Why bread goes stale and how you can unstale it

As an amateur baker, I have quite a bit of interest in bread - and if you're also a baker, you would have noticed that home-baked breads tend to get harder rather faster than the convenience breads you can buy in supermarkets.

This is, of course, no real surprise as almost all commercial bakeries need to find ways to keep bread soft and delectable-looking for a period of time on the shelves so that it maximises the chances of getting bought by people - and after that it needs to remain usable for as long as possible in the kitchen, perhaps even up to a week after purchase.

A modern loaf of bread is a somewhat curious evolution for an important food that originated some 30,000 years ago in Europe and morphed from flatbreads like khubz, lavash to modern versions like roti, chapatti and tortillas to the soft leavened sandwich loaves that you buy today.

In Germany, there are now over 1,300 varieties of breads and along the way, cakes, pastries and other wheat-based baked goods were also invented from basically the same ingredients as bread.

But I am digressing, as what I want to focus on is why my home-baked loaves get hard so quickly and how come supermarket loaves can stay soft up to a week in a plastic bag.

Firstly, let's start with why bread gets stale in the first place. You might think it is simply because the bread is losing moisture by just drying out - and that would not be a bad guess, except that it would also be quite wrong.

In 1852, a French scientist named Jean-Baptiste Boussingault hermetically sealed a loaf of bread in a special air-tight container - and the bread still went stale, despite losing no moisture at all.

What is rather more interesting is the fact that he could actually reverse the stale nature of the bread by heating it uniformly at 68°C. So that's your first tip on how you can un-stale a loaf of bread. And incidentally, it is also partly why we like toasted bread so much.

So of course, you are now curious why bread can become stale and then un-stale after re-heating at 68°C - well, you must be curious as you're still reading. The reason is quite complex but also rather interesting.

Consider what happens to a bowl of wheat flour if you just pour hot water on it and mix it around. It turns into a rather icky, gummy substance (which is also pretty inedible) because of a process called gelatinisation.

The bonds between the starch molecules are broken down in heated water, allowing the water to dissolve the soluble polysaccharides within the starch.

Basically, the crystalline structure of normal starch molecules become diffuse in heated water and separate into an amorphous form - it becomes gooey, in other words. This is the principal idea behind roux sauce, except that butter and other liquid fats are heated in combination with flour instead of water.

Why gelatinisation is mentioned is because something like it called gelation also happens in baked breads, albeit at a lesser density as the bread would have been leavened (or raised) by yeast or other raising agents.

So instead of becoming an amorphous gooey mess, gelation involves the broken down components of starch - gluten and the polysaccharides, amylose and amylopectin - to form cross-linked networked structures under heat.

The process of making home-made bread can be picked up from any baking book, so if you don't mind, we will instead investigate the chemical reactions that occur in breads during baking - which is something cookbooks rarely talk about.

In the first few minutes in a hot oven, the first product of baking bread is steam. This is very useful as a means to transport the heat of the oven evenly throughout the whole loaf and therefore help to cook the loaf uniformly.

The film of steam on the surface also stops the loaf drying out by gelating the surface starch, which will eventually become the lovely baked crust as a result of the Maillard reaction.

In the next stage, the dough becomes more fluid and expands, as gases such as steam from the water in the dough and carbon dioxide produced by the yeast start to form little pockets of hot gases.

This wobbly state is sometimes described as the "oven spring". Also, ethanol gas is involved as the fermentation process produces ethanol - and this is the compound which actually contributes the most to the aroma of baked bread.

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