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  • Writer's pictureAkis

The dark side of bread

The other day, I left my bread in the oven longer than usual and it came out like this, a bit to the dark side!

bread browning

From a visual point of view, it’s surely impressive, having all over the crust beautiful shades of golden-yellow and brown, reaching even to charred areas on the most exposed surfaces. Some people like such breads, while others prefer them less baked.

Undoubtedly, there are some positive aspects of, let’s call them, over-baked breads. They can be more desirable because, except more attractive appearance, they have developed more complex flavors and aromas, as well as a crispier texture.

However, there is also the other side of the coin with health concerns, related to foods that have been left to develop deep, dark colors, during prolonged baking.

bread browning

Browning reactions

Bakery products owe their color formation to two main chemical processes that take place at high temperatures during baking. These are the Maillard reaction and the caramelization of sugars. Ingredients of a bread dough, mainly water and flour, contain reactants to be used in the above reactions. For instance, flour is mainly composed of carbohydrates and proteins that initiate the Maillard reaction, a complex network of numerous chemical reactions that lead to the formation of compounds, known as melanoidins, which give bread crust a brown-like appearance and desirable flavors. Water is an important regulator of the Maillard reaction and it has to be in low levels for the initiation of the reaction cascade. That’s why a prerequisite for the Maillard reaction is that the temperature exceeds 100°C.

On the other side, caramelization needs only carbohydrates. Particularly, simple sugars (sucrose, fructose, glucose) are being released from starch molecules under high temperatures (>120°C) and participate in a series of not completely understood reactions that lead also to the formation of compounds with deep yellow/brown colors and caramel-like flavors, the most prevalent being hydrohylmethylfurfural (HMF) and melanoidins.

bread browning

Both Maillard reaction and caramelization occur simultaneously when the bread bakes and water content on the crust is minimized due to evaporation under high temperatures.

Quality aspects

The surface color of the bread is the most important feature that determines its acceptance by the consumer. Think yourself how you choose bread when examining the different types in a bakery. The color will point to either pleasant or boring tastes, aromas, and textures. Nobody will disagree that one of the biggest food pleasures is to eat a freshly baked baked with a crispy and golden crust. The combination of crispy texture with caramel-like flavors is unbeatable. Because of that, modern bakers tend to over-bake their breads, aiming to enhance to the maximum the feeling of pleasure. Here, I think of myself when baking my bread to hesitate to turn off the oven, always postponing it for a few more minutes and a few more...!

Nutritional aspects

However, as mentioned earlier, the development of browning in bread comes with a cost, in this case, a nutritional one. That is pronounced in the Maillard reaction that involves the usage of proteins/amino acids. The latter participating in such reactions are somehow blocked from absorption by our body and thus their bioavailability is diminished. This is particularly evident for the amino acid lysine, which is an essential one (our body cannot produce it and we have to take it from the food), and because the amino group that is contained in its sidechain is a significant source for the Maillard reaction. Furthermore, other essential amino acids like methionine and tryptophan are also lost due to oxidation.

The Maillard reaction has also been related to the production of acrylamide, a probable carcinogenic compound, which starts forming when the temperature reaches 120-130°C, in the first stage of the reaction by the condensation of sugars and the amino acid asparagine. Numerous studies have shown that bakery and potato products are major sources of acrylamide and currently scientists are working on understanding the reaction mechanisms involved in acrylamide production so as to predict and control its occurrence.

bread browning

But, there is also a positive, nutritional aspect related to bread browning that has to do with some of the end-products (melanoidins) of the Maillard reaction and caramelization. Those products have been connected with antioxidant activity because of their metal-chelating ability.

Take-home message

Now, after knowing all this information, how shall we treat over-baked bread? Personally, I still like my bread a bit to the deep-brown side. The texture and flavor are so mouth-watering that I cannot resist. In any case, all the negative issues mentioned above are only related to the crust and not to the crumb of the bread. The latter doesn’t give rise to major browning reactions because it always contains water that cannot evaporate and escape.

bread browning

Just be aware, and avoid eating by any means parts that are clearly burnt!



Purlis E. Browning development in bakery products – A review. Journal of Food Engineering (2010);99:239-49

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