If you have seen or consumed a plated dessert containing small pearls bursting full of flavour, they were most likely made via spherification. Spherification is a process discovered by the company Unilever in 1942. The process involves using an extract from seaweed called alginate, and calcium to form a gel which contains flavourful liquid. Alginate is known as a hydrocolloid, which are compounds that disperses into, and absorbs water, effectively thickening the solution. When an alginate solution makes contact with a solution containing calcium ions, the alginate will start to gel, forming a membrane.
Figure 1: Crosslinking of alginate strands with calcium ions
As seen in Figure 1, sodium ions in the sodium alginate are exchanged with calcium ions, forming cross linkages, which cause the alginate to gel on the surface. Surface tension causes the droplet to become spherical, provided that the drop is completely submerged in the solution. The sphere cannot be submerged in water for a prolonged period of time; the flavourful liquid will slowly flow out, while the water will flow in, diluting the flavour.
Figure 2: Tools and ingredients used for basic or reverse spherification.
There are a few methods of spherification: basic, cold oil, reverse, and frozen reverse spherification, all with advantages and disadvantages. The two widely used methods are basic and reverse spherification. In basic spherification, the alginate is blended in the flavourful liquid. Droplets of this solution are placed into a calcium chloride bath, and then the excess calcium is rinsed off with water. The advantages of basic spherification include: spheres having a very thin membrane, resulting in a delicate mouth feel, and a rounder sphere, as the calcium bath has low viscosity. Disadvantages of basic spherification are the inability to use with liquids with high calcium content, as premature gelling would occur, and the inability for alginate to hydrate well in high alcohol solutions. Spheres made from basic spherification cannot be stored long, as the gelling process continues even after rinsing with water. The calcium ions eventually migrate into the alginate pearl, which will cause the entire sphere to become a gel, losing the effect of the pop.
Figure 3: Strawberry spheres with black pepper, made via reverse spherification
In reverse spherification, the opposite occurs; neutral flavoured calcium gluconate lactate is blended with the flavourful liquid. This solution is dropped into a bath containing alginate, and then rinsed. Reverse spherification addresses the problems that occur in basic spherification. A wider variety of flavourful liquids can be used, including liquids containing calcium and higher levels of alcohol. Since the migration of calcium ions from reverse spherification are from the inside-out, the process stops once the pearls are removed from the alginate bath. Prolonged storage of gels will still yield a popping effect with flavourful liquid intact. The membrane from reverse spherification is thicker, which will affect mouth feel; however, this can be used as an advantage when making larger dessert spheres; more structure is needed to support the liquid weight, as seen in Figure 3. A disadvantages of reverse spherification is that it is more difficult to obtain a perfectly spherical pearl. Since the final alginate bath is more viscous, deforming can occur. Furthermore, pearls made with reverse spherification are more prone to sticking to each other, so the alginate bath must be sufficiently agitated.
Figure 4.1 (Left): Cheesecake with black currant pearls, and a side of mint pearls
Figure 4.2 (Right): White chocolate panna cotta with hibiscus pearls
Spherification is highly versatile. As seen from Figure 4, pearls are often colourful, shiny, and uniform, which can add to the perceived value of a food. On plated desserts, sauces or coulis can be substituted by pearls, adding mouth feel. This application avoids the problem of sauces potentially running and soaking into other components of the plated dessert. Pearls can be placed on small cookies or petit fours, which will not only make the food more attractive, but will add a concentrated taste. Applying appropriate techniques, virtually any flavourful liquid can be made into pearls. With the knowledge of spherification, anybody can make incredibly beautiful, dramatic looking desserts; the only limit is one’s imagination.
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