The first thing that comes to mind talking about gelatine is traditional jelly, that seems semi-solid in appearance, but melts in your mouth when you eat it. Have you ever tried it?
Jelly is a classic example of gelatine, but it is actually used in many sweet dishes such as fruit desserts, marshmallows, and gummy bears, but also in savoury dishes such as chicken in gelatine and some types of Chinese dumplings, etc.
It is also used as a thickener in yogurts, cheeses, and margarine.
What makes gelatine so special, and interesting enough to be discussed in this column?
It is a chemical compound with very distinctive properties: if dissolved in hot water, it mixes with it and the compound behaves like a liquid or a solid (or rather, like a gel) depending on the temperature.
You may say that this is not even news, even without adding gelatine water is a liquid and when frozen it becomes a solid.
Basically, you are right, however the “solid” or “gel” state of the compound in which the gelatine was mixed only occurs in a very special range of temperatures.
This range is between 4 degrees, at which temperature the mixture begins to crystallize, and 35 degrees.
The fact that it melts precisely at 35 degrees is particularly important, because it is just below body temperature. In this way, a gelatine dish served at around 20 degrees behaves like a strange gel, but when eaten, it melts in your mouth!
First of all, let’s better define what I mean by the “solid state” of gelatine. As I said, it’s not a true solid state, but more of a gel.
The below YouTube video by Modernist Cuisine helps to clarify the matter as you can see a cube of gelatine dropping onto a hard surface, filmed at high speed.
It is quite mesmerizing!
So now you understand what I mean? It is clearly very different to a liquid; the cube walls deform a great amount without ever being destroyed. In other words, it is gelatinous.
Now for the technical details. The concept is actually quite simple.
Gelatine is a chemical compound formed by long chains of the amino acids that make up proteins, with some hydrogen atoms at the ends.
These chains tend to stick to each other very easily, forming rather complex three-dimensional structures.
However, when heated they melt as shown in the figure.
If we dissolve these chains in hot water and subsequently cool them to the temperatures mentioned above, below 35 degrees, the chains begin to form with an interesting additional detail: the hydrogen molecules present at the ends form hydrogen bonds with the water molecules.
The hydrogen bond is a very unusual bond, because it allows hydrogen atoms to bind to the negative partial charges of some particularly electronegative molecules, such as fluorine, oxygen, and nitrogen.
It is weaker than other intermolecular bonds (such as the covalent bond forming two hydrogen atoms and one of oxygen, aka, the water molecule), but strong enough to form a resistant structure.
So basically, these chains are linked to each other and to the water molecules, forming a kind of internal skeleton, that is stiffer than a liquid, but notably more flexible: gelatine!
The process by which the compound turns to liquid by heating is also simple: heat agitates the molecules in the water, breaking the weakest bonds, i.e. the ones that form the chains of amino acids and which bind them to water molecules.
The water molecules need a much higher temperature to be broken, so the compound simply returns to a liquid state.
That explains the secret of gelatine in a nutshell. Thanks to its characteristics, as we were saying, it can be very useful in the kitchen, even for artistic creations, such as the flowers created in the below Gelatin Art Market Store video.
Matteo Biagetti – Science Blogger @Gushmag Network