Edible liquid bubbles were originally developed for molecular gastronomy chef Ferran Adrià. Now, start-up company Skipping Rocks Lab has turned this into Ooho! – a bite-sized blob of water. The water is contained in an edible membrane that is made from two tasteless ingredients: sodium alginate (usually derived from seaweed) and calcium chloride. Both are already used in the food industry and are completely safe. Currently, the membrane only lasts a few days before breaking down but the developers are working on tougher versions that could be licensed to drinks companies.
Water is frozen into a ball so that it holds its shape, and to keep the water molecules from mixing with the membrane chemicals.
The ice ball is dipped into calcium chloride solution. The outer layer of ice melts and some of the calcium ions diffuse in.
A second bath in warm sodium alginate solution forms the membrane. Calcium ions replace sodium atoms in the alginate and bind the molecules together.
Unlike sodium, calcium has two positive charges. This lets it bond to two alginate chains at once, tangling them up.
After two to five minutes, enough of the alginate molecules have polymerised together to form a stable skin and the ice melts into a liquid centre.