The technique known as spherification consists of obtaining semi-solid or gelatinous spheres, similar to fish roe, from liquid or creamy elements. This technique is used in cuisine to create unique dishes, but it is also used in medicine to encapsulate cells and protect them from external factors that could damage them, or to release drugs in a controlled way.
The state we are looking for, gel, is between liquids and solids. It does not flow, but it is not crystalline either. The change in the state is provoked because some links are generated between the atoms or chains that form the material, trapping water inside. Scientifically, this process is called “crosslinking”.
This is what is done in the spherification: compounds (salts normally, like CaCl2) are added to some special liquids, in order to obtain this gelatins. There is a huge variety of materials that can be used for this aim, but maybe alginate is the most common and for this reason, easy to find and cheap.
BASIC PROTOCOL FOR ALGINATE SPHERIFICATION
- Sodium alginate (1-8 gr/100 mL, depending on the desired density. Recommended: 3%)
- Calcium Chloride (1-4 gr/100 mL. Recommended: 2%)
- Hot water (<60ºC)
- 2 Containers (one for alginate dissolution and one for chloride solution)
- Tools to create drops: Pipette or dropper, straw, perforated spoon, etc.
- Make alginate and chloride solutions, dissolving the desired amount in hot water*. We already have the two containers prepared, the one of calcium chloride (1) [liquid] and the one of alginate (2) [more viscous].
- Take the alginate (2) with the choosen tool and deposit the drops onto the calcium chloride container (1).
- Let stand for 5 minutes
- Remove the spheres with a spoon, or filter through a strainer.
- We have the spheres ready!
You can play with the height at which the drop or the nozzle is deposited to change the size of the spheres. If food dye is added to the alginate, the spheres already formed can be seen better. If it is also added to the chloride, you can see how the spheres are stained in both colors at the end. It can be used to explain diffusion at school.
* Alginate may require a lot of agitation and time to dissolve completely. It may also help to use warm water.