With intense happiness I was eating a roasted piece of bread, also known in the english vernacular as: toast. It might have been because I was hungry, but the transformation of a piece of stale bread into a wonderfully tasting, almost superreal, experience by heating it is simply amazing. It is the warmth, the flavours, the colour, everything about it amazes me. As if the bread had been reanimated and had been given a second chance.
The butter I put on it, melts like sun lotion and makes the surface glisten in the early morning light. I have to move quickly now, the heat is radiating away and the temperature drops when I reach for the honey. To make it a swift and painless execution I bite the first piece off which only has butter on it. The aromas are filling my mouth and the sunflower seeds which had been stuck to the bottom fall off and land on my tongue as if they were parachutists dropped to supply the needy and hungry with sustenance.
Alright, I might have been a bit too lyrical writing that, yet you cannot deny that toast is natures encore to humanity for inventing bread. The chemical reaction that makes it all possible is the famous Maillard reaction.
Where proteins and carbohydrates meet
The Maillard reaction is not a simple one, in fact far from it. And we are venturing here in the domain of organic chemistry which is a particularly smelly and sticky business. There are millions of ways one can organise a handful of carbon and hydrogen atoms along with the occasional nitrogen atom here and there. The amount of compounds is enormous!
For this particular reaction one needs amino acids and a sugar, a reducing sugar to be precise. Toast is heated but the Maillard reaction can also take place at lower temperatures, though, like any chemical reaction, the higher the temperature the faster the reaction takes place. The sugars donate electrons from their carbonyl group (the double bond C=O group), thereby reducing the compound they're donating the electrons to. This produces glucosamines and water. The glucosamine undergoes Amadori rearrangement in which the groups are rearranged and products called ketosamines are formed. These ketone and amine compounds then react further to produce a wealth of reductones (a type of antioxidants), and a load of other short chain molecules as a byproduct of hydrolysis is formed, including diacetyl (which is the compound that gives butter it's flavour), aspirin (also a small cyclic molecule) and other aromatic* and non-aromatic compounds. Also brown substances called melanoidins are formed, which we have encountered in an earlier episode about foam as the brown substance in coffee crema.
All these organic compounds yield different flavours. As they appear in different concentrations at different times there is a progression of flavours during the making of the toast. One has to be careful not to let the toast warm too long or it will get burnt. At that point bitter substances like polycyclic aromatic hydrocarbons (PAHs) are formed. These are believed to be carcinogenic.
Another substance which has been found in starchy foods that have been heated is acrylamide, a neurotoxic substance. It has been found in crisps and chips for example, and the food industry is monitoring it ever since its discovery in 2002. It is believed to be a byproduct of the Maillard reaction in the aminoacid Asparagine and a carboxyl group, however, it is not yet completely clear how the reaction that produces it takes place. It seems heating our food isn't solely beneficial.
Apic reflux
Thinking about toast one cannot forget honey, they form an almost inseparable companionship. Honey is a strange substance; it is literally apic regurgitation (or bee vomit in slightly less appetising wording), and it has a number of interesting properties. First of all it is a mixture of mostly fructose and glucose, and the ratio depends on the type of honey. Natural glucose polarises light right handed (+52.7 degrees) (which is clear from its alternate name dextrose, dextro: the latin for right) and natural fructose polarises light left handed (-92 degrees). By shining unpolarised light through a mixture of glucose and fructose one can determine the ratio of the two by analysing the polarisation of the light passing through. (Interestingly bees can actually see polarised light, though not circular polarisations - the only creature not having to wear special glasses at the 3D cinema is the Mantis shrimp.)
There is more to honey than meets the eye. Next to the huge amounts of glucose and fructose it contains trace amounts of amino acids, mainly proline. Honey doesn't 'go bad' even after a long time in storage. The reason is mainly that the high monosacharose and low water content prevent any fermentation or the growth of bacteria. Leaving honey in the jar for a long time does cause a few effects. In essence honey is a supersaturated liquid, in which monosaccharides are dissolved. In time these will start to crystalise. This crystalisation can be easily reversed by slow heating which will melt the crystals into an amorphous state again. When honey is left for several years one can notice a browning of the substance. This browning is caused by the slow reaction of the residual amino acids with the sugars, in what is a very slow Maillard reaction. There have been reports of honey found in pharao tombs that was still edible. I'm not sure I would try though. The Maillard reaction probably also causes some different flavours to appear.
Finally the Maillard reaction is catalysed in an alkaline environment. Marinating meat in baking soda or egg whites will make them brown more readily. Don't use too much baking soda though, or the fat in the meat will turn into soap.
So, one might wonder, how is this different from caramelisation? In essance caramelisation is 'just' a thermolysis of the carbohydrates and oxidation. There are no amino acids involved and hence a different flavour spectrum. No S and N compounds (that is sulfur and nitrogen, if you're into that sort of thing), so one wouldn't get any of the nasty (or delicious) aromas associated with for example meat or other kinds of roasted proteins. All in all a very complex, experimental biochemistry, but it does produce some very yummy results when done in a proper environment with the right ingredients.
*) Aromatic in the chemical sense means the molecule is in a ring structure with unsaturated bonds, allowing the valence electrons to roam freely through the molecule, it doesn't attribute any olfactory stimulating properties per se.
The butter I put on it, melts like sun lotion and makes the surface glisten in the early morning light. I have to move quickly now, the heat is radiating away and the temperature drops when I reach for the honey. To make it a swift and painless execution I bite the first piece off which only has butter on it. The aromas are filling my mouth and the sunflower seeds which had been stuck to the bottom fall off and land on my tongue as if they were parachutists dropped to supply the needy and hungry with sustenance.
Alright, I might have been a bit too lyrical writing that, yet you cannot deny that toast is natures encore to humanity for inventing bread. The chemical reaction that makes it all possible is the famous Maillard reaction.
Where proteins and carbohydrates meet
The Maillard reaction is not a simple one, in fact far from it. And we are venturing here in the domain of organic chemistry which is a particularly smelly and sticky business. There are millions of ways one can organise a handful of carbon and hydrogen atoms along with the occasional nitrogen atom here and there. The amount of compounds is enormous!
For this particular reaction one needs amino acids and a sugar, a reducing sugar to be precise. Toast is heated but the Maillard reaction can also take place at lower temperatures, though, like any chemical reaction, the higher the temperature the faster the reaction takes place. The sugars donate electrons from their carbonyl group (the double bond C=O group), thereby reducing the compound they're donating the electrons to. This produces glucosamines and water. The glucosamine undergoes Amadori rearrangement in which the groups are rearranged and products called ketosamines are formed. These ketone and amine compounds then react further to produce a wealth of reductones (a type of antioxidants), and a load of other short chain molecules as a byproduct of hydrolysis is formed, including diacetyl (which is the compound that gives butter it's flavour), aspirin (also a small cyclic molecule) and other aromatic* and non-aromatic compounds. Also brown substances called melanoidins are formed, which we have encountered in an earlier episode about foam as the brown substance in coffee crema.
All these organic compounds yield different flavours. As they appear in different concentrations at different times there is a progression of flavours during the making of the toast. One has to be careful not to let the toast warm too long or it will get burnt. At that point bitter substances like polycyclic aromatic hydrocarbons (PAHs) are formed. These are believed to be carcinogenic.
Another substance which has been found in starchy foods that have been heated is acrylamide, a neurotoxic substance. It has been found in crisps and chips for example, and the food industry is monitoring it ever since its discovery in 2002. It is believed to be a byproduct of the Maillard reaction in the aminoacid Asparagine and a carboxyl group, however, it is not yet completely clear how the reaction that produces it takes place. It seems heating our food isn't solely beneficial.
Apic reflux
Thinking about toast one cannot forget honey, they form an almost inseparable companionship. Honey is a strange substance; it is literally apic regurgitation (or bee vomit in slightly less appetising wording), and it has a number of interesting properties. First of all it is a mixture of mostly fructose and glucose, and the ratio depends on the type of honey. Natural glucose polarises light right handed (+52.7 degrees) (which is clear from its alternate name dextrose, dextro: the latin for right) and natural fructose polarises light left handed (-92 degrees). By shining unpolarised light through a mixture of glucose and fructose one can determine the ratio of the two by analysing the polarisation of the light passing through. (Interestingly bees can actually see polarised light, though not circular polarisations - the only creature not having to wear special glasses at the 3D cinema is the Mantis shrimp.)
There is more to honey than meets the eye. Next to the huge amounts of glucose and fructose it contains trace amounts of amino acids, mainly proline. Honey doesn't 'go bad' even after a long time in storage. The reason is mainly that the high monosacharose and low water content prevent any fermentation or the growth of bacteria. Leaving honey in the jar for a long time does cause a few effects. In essence honey is a supersaturated liquid, in which monosaccharides are dissolved. In time these will start to crystalise. This crystalisation can be easily reversed by slow heating which will melt the crystals into an amorphous state again. When honey is left for several years one can notice a browning of the substance. This browning is caused by the slow reaction of the residual amino acids with the sugars, in what is a very slow Maillard reaction. There have been reports of honey found in pharao tombs that was still edible. I'm not sure I would try though. The Maillard reaction probably also causes some different flavours to appear.
Finally the Maillard reaction is catalysed in an alkaline environment. Marinating meat in baking soda or egg whites will make them brown more readily. Don't use too much baking soda though, or the fat in the meat will turn into soap.
So, one might wonder, how is this different from caramelisation? In essance caramelisation is 'just' a thermolysis of the carbohydrates and oxidation. There are no amino acids involved and hence a different flavour spectrum. No S and N compounds (that is sulfur and nitrogen, if you're into that sort of thing), so one wouldn't get any of the nasty (or delicious) aromas associated with for example meat or other kinds of roasted proteins. All in all a very complex, experimental biochemistry, but it does produce some very yummy results when done in a proper environment with the right ingredients.
*) Aromatic in the chemical sense means the molecule is in a ring structure with unsaturated bonds, allowing the valence electrons to roam freely through the molecule, it doesn't attribute any olfactory stimulating properties per se.
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