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Why Does Bread Shrink in the Toaster?

Why Does Bread Shrink in the Toaster?

Have you noticed that your white bread slices tend to shrink when you toast them? I wanted to know why and decided to do some research online. 

White bread contains a significant amount of moisture, which evaporates when the bread is heated in the toaster. This process will shrink your bread slice, making it both smaller, lighter, and dryer than an untoasted bread slice. 

Keep reading this article and find out exactly how much bread shrinks while being toasted, if all bread types shrink in the toaster, and if toasted bread lasts longer than untoasted.  

Why Does Bread Shrink When it Is Toasted?

two slices of white bread getting toasted

The hot air in your toaster reduces the moisture of the toasting bread slice significantly, causing it to lose weight and volume and hence shrink.

The heating causes the water within the bread to evaporate, making it smaller and dryer than a untoasted slice of bread. 

For this to happen, the air in your toaster must reach a temperature range of 285 to 320F (140 to 160C), which is the maximum temperature range in most toaster models available today. 

For the air to get that hot, the toaster’s heating element (made of nickel-chromium alloy) typically reaches temperatures of 1,100 to 1,200F (590 to 650C). 

With such a temperature range in the toaster, your bread slices will be toasted in a matter of minutes. 

And the longer you let your toaster run, the browner, more toasted, and shrunk your bread gets.

The browning of toast is due to the Maillard reaction that takes place during the heating process.  

This chemical reaction occurs when the bread’s sugars react with its amino acids, forming a complex mixture of molecules responsible for toast’s so well-known brown color. 

This reaction also gives our toast its characteristic flavor, aroma, and texture. 

How Much Does Bread Shrink While Toasting?

a half slice of untoasted bread next to a half slice of toasted bread

I wanted to know exactly how much a regular slice of toast bread shrinks while it’s being toasted, so I took a fresh, untoasted slice and a toasted one, cut them in half, and weighed and measured both of them. 

You can see from the picture above that the difference is not huge, but definitely noticeable!

Also, I toasted my slice for about 3.5 minutes, which is the standard time for most toasters. It can be assumed that the longer the bread gets toasted, the more water and mass it’ll lose. 

two half slices of toast bread being weighed

My standard-toasted slice of white bread did lose about 0.1 ounces in weight and shrunk about 0.08 inches on each side. 

This doesn’t sound huge, but if you consider that a standard slice of toast weighs about 1.4 ounces, 0.1 ounces equals about 7% of its total weight.

But as toast tastes delicious, that 7% doesn’t matter all that much! 

Does All Bread Shrink in the Toaster?

Most white bread holds more moisture than dark or brown bread types (which is also why white bread generally molds faster), so not all bread is toasted equally!

Hence, brown, whole-grain bread slices won’t shrink nearly as much as conventional white bread slices will when it is toasted.

I have never noticed any difference in size when I toast my brown bread slices at home!

And so, if it indeed shrinks, the change must be minimal, as it just doesn’t contain that much moisture to begin with.

Does Toasting Bread Increase Its Shelf Life?

The less excess moisture a food contains, the longer it generally lasts. And so, as almost all the water exits your bread while it is heated, toasting it can undoubtedly increase the bread’s shelf life.

The only problem is that toasted bread will become very dry and stale after only a day, so the prolonged shelf life is of no actual use.

Unless that is, you plan on using your dry, toasted bread for something else.

Old toast makes for excellent bread crumbs, for example!

And so, if you keep it in a dry, cool place and away from moisture, your toasted bread may last for several days or even weeks (depending on the brand and amount of preservatives)!

PLEASE NOTE: Always check for mold on your bread, no matter how safe and dry you’ve stored it! Additionally, if your bread smells or tastes bad, off, sour, or bitter, you should never consume it!

Does Toasting Bread Keep It From Molding?

Any food containing water or other fluids can get moldy, as mold needs moisture to grow.

Hence, toasting your bread, and thereby eliminating all or most of its moisture, can prevent it from developing mold! 

However, there is no 100% guarantee for this, as some excess moisture might be left in your toast.

This can depend on factors such as:

  • the type and brand of bread (and flour)
  • the amount of heat in the toaster
  • the amount of time the bread gets toasted
  • the amount of moisture in the fresh toast bread

Generally, the risk of mold in or on toasted bread is small, but you can never be sure!

On the other hand, toasting already moldy and spoiled bread will not kill the mold

PLEASE NOTE: Never consume moldy bread (toasted or untoasted), as mold can be hazardous to your health!

Is Toasted Bread Healthier Than Untoasted Bread?

a slice of toast with butter on it.

While toasting your bread won’t change its nutritional value, amount of carbohydrates, or calories, it can decrease the bread’s glycemic index.

The glycemic index (GI) shows how quickly a food affects your glucose (blood sugar) levels when eaten on its own. 

As white bread contains a lot of carbohydrates, it is considered a high GI food, meaning that toasting it can have a slight positive effect on your health. 

On the other hand, toasted bread can contain significant amounts of acrylamide, a carcinogen (a substance promoting cancer formation).

Acrylamide is generated during the browning process of the toast. And the darker the surface of your toast, the higher its acrylamide concentration will be. 

That’s why it is generally recommended that you toast your bread to the lightest color possible.   

However, it must also be stated that since 2019, studies suggest that dietary acrylamide consumption unlikely leads to an increased risk of getting cancer. 

Nevertheless, as well-toasted bread can also contain Benzo[a]pyrene, an aromatic hydrocarbon that can also be found in coal tar and tobacco smoke, I tend to stay away from toast with a very dark color. 

Does Toasting Stale Bread Make It Better?

You can revive your stale bread with moisture and heat and make it relatively delicious and fresh again. 

All you need to do to bring your rock-hard bread back to life is to sprinkle some water onto it and then either put it in the:

  • toaster
  • oven
  • or microwave

The bread’s starch will reabsorb the water with the help of heat (it’s a reversed toasting process), making your bread slice soft, fresh, and tasty once again!

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