How does gelatin interact with grease (fat)?
I made an escalivada (eggplant, red pepper and onion in the oven, peel, cool) yesterday, and today I've added gelatin to make a nice presentation.
I used about 5gr of gelatin for 150ml heated 'escalivada juice (lots of olive oil)'.
The result was all right, but the top layer stayed liquid. The rest stayed together.
Any idea as to why the top layer stayed liquid? Does the olive oil affect the gelatin?
Best Answer
Gelatin works by creating a very fine mesh of proteins, between which the (hidrophilic) liquid gets trapped.
A mixture of fat and water isn't a liquid. It can be either a rough two-phase mixture, with visible fat droplets swimming around in the water, or it can be an emulsion, with invisibly small fat droplets dispersed through the water. Emulsions appear smooth, e.g. milk.
When you try to use gelatine on the mixture, two things can happen. In an emulsion, the fat droplets can be smaller than the protein mesh. Then they get trapped as well as the water, and the result is gelled emulsion, just like you'd expect.
But if you have big globules of fat, they can't be trapped between the proteins. So it looks like they got squeezed out of the mesh and bubbled up to the surface, if it hadn't been there all along. On the surface, gelatine molecules couldn't find each other between globules of fat to crosslink, or maybe the motion of the globules broke any nascent links in the small amount of water between them, so it couldn't gel. So the conclusion is: you can't set soup/stew with gelatine. (I know that concentrated stock hardens from its own gelatine, but it has the fat filtered out first).
On the practical side, if you want to have thick stew juice, you have to use something else than gelatine. It is probably simplest to create an olive oil based roux with the stew juice. Or you can gel with xanthan. Both will result in a "juice" which is creamy, instead of solid wobbly blocks of juice, with xanthan retaining the authentic taste and a roux-based sauce being a novel variation.
If it is real jelly you are after, you'll have to emulsify first and use gelatine after that. Xanthan itself should emulsify well, or you can probably use lecithine. AFAIK, there is no problem to use lecithine and gelatine together, but somebody with more experience in gelling agents should confirm that. In any case, emulsifying will lead to your liquid getting quite opaque. This is inavoidable, as it has to do with the way the collection of individual micro fat droplets break and reflect light rays.
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What happens when you mix gelatin and oil?
When warm gelatin is dropped in oil however, the gelatin stays together in little spheres. This happens because water and oil do not mix. Gelatin particles shy away from oil so they clump together in the shape that gives the least possible interaction with oil: a sphere.Does gelatin bind fat?
All I've been able to find is general information that gelatin binds small fat droplets and that larger droplets result in a greasy mess, with no specifics on droplet size or volume.Does gelatin dissolve in oil?
Gelatin is soluble in glycerol and acetic acid, and more soluble in hot than in cold water. tetrachloride, ether, benzene, acetone and oils. indefinitely, but at elevated temperatures hydrolysis or rupture of peptide bonds occurs, increasing the number of free amino groups.Does gelatin emulsify oil?
Gelatins are important natural amphiphilic macromolecules and can act as emulsifiers in oil-in-water emulsions due to their surface-active properties.Tips and Tricks to Gelatin Success - Kitchen Conundrums with Thomas Joseph
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