A modernist surprise
One of the iconic modernist techniques is spherification.
As an industrial technique it has been around a long time (circa 1973), but in a basic way. It was Ferran Adria who first realized its culinary potential when, in 2001, he saw it being used to make small pearl-like gels for a mexican sauce at an industrial food packaging plant.
By 2003, and after many trials, he had refined this technique and created a new culinary method that enclosed flavourful liquids in a thin sac made of itself — a spherical ravioli of whatever you want.
This is Adria’s spherified pea juice:
On eating, the sac ruptures, and the sudden release of its juicy content produces a vivid burst of pea flavor in the mouth.
The technique involves a gelling agent (sodium alginate) that gels rapidly in the presence of calcium ions.
Sodium alginate is refined from brown seaweeds, such as kelp. These seaweeds are slimy to the touch because they produce alginate on their surface that gels when it comes into contact with sea-water, which is high in calcium (it’s what makes crustacean shells and coral possible). The alginate is also a thickening agent when mixed with water, so the combined result is a viscous surface gum forming a protective layer for the fronds.
So this is what Ferran et al. did: Mix sodium alginate into pea juice. Make up a separate water bath containing calcium chloride. Drop teaspoons of pea juice into the calcium bath and wait a little while. Surface tension forms the drops into approximate spheres, and the calcium sets (gels) the surface of the spheres thereby containing the juice.
He then refined it further by reversing the process: Put the calcium into the juice, and the alginate into the water bath, and proceed as usual. The advantage of this is that because the alginate is only present on the surface, rather than dispersed throughout the juice, it cannot continue to set the sphere and the interior remains fluid. If you wait too long with the first method, the whole sphere eventually gels.
There are a number of demonstrations of this technique on the web, including by Ferran himself (see video). It can be done at home with a little practice, and the ingredients can be found online.