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Spherification: Sodium Alginate (SA), Calcium Chloride, & Sodium Citrate
These ingredients may be used to create spheres of fruit, vegetable or herb purees, which gel on the outside but retain a liquid centre.
Using a technique referred to as “Spherification” it is possible to create fruit and vegetable “caviar” (beads) and “ravioli” (larger flexible spheres).
The technique for the spherification process was first pioneered by Ferran Adria of El bulli restaurant, who demonstrated how a reaction between water-soluble sodium alginate (mixed with a fruit puree) dropped into a water bath containing calcium chloride formed a controlled gel network at the point of contact encasing the remaining liquid. He defined this concept in to two basic methods:
Basic Spherification:
Where a liquid containing sodium alginate is submerged in a bath of calcium chloride
Reverse Spherification:
Where liquid containing calcium is dropped into a water bath containing sodium alginate.
(See the calcium gluconolactate (CLG) post for more information on reverse spherification).
The ingredients:
Sodium alginate (SA)
The sodium salt of alginic acid, sodium alginate is an extract of seaweed. It is used widely in the food industry in its gum form as an emulsifier. Sodium alginate has no discernible flavour.
Calcium Chloride:
Calcium Chloride is a chemical compound of calcium and chlorine.
It is highly hygroscopic and must be stored in a sealed container or it will eventually self-dissolve in the water that it absorbs from the air.
Calcium chloride has a slightly bitter taste so after “poaching” fruit “caviar” the pearls are rinsed with water before consumption.
Sodium Citrate:
The sodium salt of citric acid, sodium citrate is utilised in some spherification recipes as a buffer to control acidity, resisting changes to the pH of a solution so as to enable the successful setting of the surface gel network when using acidic ingredients.
Guideline concentrations for the basic spherification process:
Fruit or vegetable puree blended with 1-2% of sodium alginate
Water with the addition of 2.5gm of calcium chloride per 500ml. (0.5%)
Example Recipes:
Pear Caviar
Spherification bath:
Add 2.5gm of calcium chloride to 500ml of water for a “poaching” bath solution, whisk to dissolve and refrigerate until required.
Pear Alginate:
Bring the water to the boil; mix the SA with the sugar and “rain” into the boiling water. Stick blend the solution or transfer to a bar blender and process to ensure that the alginate is completely dissolved, leave to rest & cool.
Juice the pears to yield 100gm of juice by weight add the vitamin C & blend in half of the alginate solution, (reserve the remaining solution). Mix well with a stick or bar blander & rest to allow any incorporated air to escape.
Technique:
Place a strainer into the spherification bath and spoon a small drop of the pear mixture into the bath as a test. Lift the strainer to remove after approximately 10 seconds.
The exact set of the caviar is determined by the acidity of the fruit and the immersion time in the chloride bath, if Spherification isn’t achieved blend more of the remaining sodium alginate solution into the pear puree and retest.
When the correct mix has been achieved fill a syringe or squeeze bottle with the pear-alginate mixture and squeeze droplets into the bath. Allow to “poach” for 10-20 seconds then remove the “caviar” and rinse in cold water to remove the surface chloride solution before serving.
Espresso Caviar
Spherification bath:
Add 2.5gm of calcium chloride to 500ml of water for a “poaching” bath solution, whisk to dissolve and refrigerate until required.
Coffee Alginate:
Mix the SA with the sugar and “rain” into the hot coffee. Stick blend the solution or transfer to a bar blender and process to ensure that the alginate is completely dissolved. Refrigerate for at least 1hr.
Technique:
Fill a syringe or squeeze bottle with the coffee-alginate mixture and squeeze droplets into the spherification bath. Allow to “poach” for 10-15 seconds then remove the “caviar” and rinse in cold water to remove the surface chloride solution before serving.
Mango “Caviar” in the style of El Bulli
For the fruit-alginate solution:
Spherification bath:
Add 2.5gm of calcium chloride to 500ml of water for a “poaching” bath solution, whisk to dissolve and refrigerate until required.
Mango Alginate:
Bring the water for the fruit solution to the boil and incorporate the SA with a stick blender, (or transfer to a bar blender and process to ensure that the alginate is completely dissolved).
Cool the solution and whisk in the flavour drop, mango puree & sodium citrate. Refrigerate the mix & rest for 1hr (or until required) to remove any air incorporated by the mixing process.
Technique:
Transfer the mango-alginate mixture to a syringe or squeeze bottle and repeatedly drop small beads into the water bath. Remove after 15-20 seconds & rinse in fresh cold water before serving.
Summary & Other Uses
Alginates react to form a gel where they meet with calcium. This process continues until the calcium supply is removed. i.e. by rinsing in fresh water. Alginate solutions, which are left in a calcium-poaching bath, will continue to gel until solid and even after removing form the bath will continue to thicken slowly on the surface of the formed sphere. For the lightest possible encasement membrane they should be prepared close to the time of serving.
As well as the production of spherical liquid carriers the alginate-calcium reaction can be used to form gels for other uses:
For a Gel Coating:
Food can be dipped into an alginate solution and then into a calcium bath.
For Wrappings:
A thin layer of alginate solution can be sprayed with a calcium solution from an aromatiser to form a thin flexible layer for use as a wrapping.
For Brittle Films:
A thin alginate solution, which has been dried, will obtain a thin brittle flavoured film.
For Gels:
A hot alginate solution mixed with a hot calcium solution will form a heat stable gel.
Once formed alginate-calcium-structures are heat stable, they can be heated by steaming, adding to hot liquids or (depending on recipe) deep-fried.
Note - Tips for spherification
Do not use hard tap water (substitute bottled or filtered), tap water varies
