One of the really appetising features of a nice-looking loaf, I find, is how caramelised the crust is. Often because I cannot wait to dig my teeth into this wonderfully semi-sweet hard and thick piece of yumminess, but also because it tells a story, the story of how well the baker managed to unleash the sugars naturally present in the flour.
Imagine yourself looking at two different book covers on bread making. The cover of book number one is illustrated with a magnificient loaf baked with love and care, with colours ranging from creamy yellow to dark reddish brown. On the second book is a pale brick of dough, hardly cooked and dull.
Sounds familiar? Which book would you rather go for?
This brownish colour is in fact due to the Maillard reaction, which is strictly speaking slightly different than caramelisation.
Caramelisation is what happens when sugars are heated to a high temperature (120-150C). The Maillard reaction undergoes the same process but proteins are also involved in the reaction. This makes the browning happen faster and at a lower temperature. In fact the Maillard reaction can even happen at room temperature. Take white chocolate for example or dry milk, both of which will develop a brownish cast over time due to Maillard browning, only this time it is not desirable.
Only small amounts of proteins are needed to speed-up that browning process. This is why for example sweet-dough that contain a lot of milk, eggs and sugar will brown really quickly.
The reaction of caramelisation is fascinating. As sugars are heated, they are broken down into smaller molecules that escape and excite our olfactory nerves. As the heating process goes on, these molecules react with one another and generate polymers. These polymers (meladoidins) do not evaporate but absorb light, imparting a brown colour. At the same time LOAAADDSSSS of flavour compounds are also created, for the joy of our tastebuds.
The chart below found on https://toastingtoast.files.wordpress.com talks about up to 54 unique flavour compounds created, but other sources are referring to hundreds. It seems that although this reaction has been studied for over a century, it is so complex that many of its pathways are still unknown.
In case you are wondering who that bloke is in the top left hand corner of the illustration, let me introduce you to French scientist Louis Camille Maillard (1878-1936), who studied the reactions of amino acids and carbohydrates in 1912 as part of his PhD thesis.
And here are the 3 stages of Maillard reaction, broken down:
Coming back to our loaf of bread now. If you pull a loaf of bread out of the oven that lacks colour, chances are that Mr Maillard was not on your side. One reason could be that the fermentation process has gone a bit too far and most of the simple sugars have been consumed by the yeasts, or it could be that the conversion of complex sugars into carbohydrates has not had time to occur. This leads us to one of our next topics: Fermentation.
Thanks for reading!
references: http://www.food-info.net/uk/colour/maillard.htm "How baking works", by Paula Figoni.