As you perhaps would expect, the use of seaweed as something you eat rather than use in a hole dug for a clambake on the beach traces back to ancient Japan. I’ve said it before and I’ll say it again: is there anything the Japanese won’t eat? The Japanese as well as many health conscious individuals of all nationalities are quite willing to consume seaweed in its raw form. The fact is that seaweed is not really considered an ingredient of ice cream; it is used as stabilizer. Without the carrageenan and alginates in ice cream it would become kind of grainy after sitting in the freezer for a while. The process of making ice cream at a retail level creates through the process of freezing intensely tiny ice crystals that are roughly one micron. To give you an idea of just how small these crystals are, a micron is equal to one-thousandth of millimeter.
Your freezer has a thermostat inside it that continually switches the refrigerator on and off. As this happens, there is a subsequent fluctuation in the temperature inside the freezer. When the temperature rises slightly, the ice melts and water crystals develop. When the temperature goes back down a freezing effect takes places. This process essentially has a coarsening effect on the ice cream and can lead to it exhibiting certain textural difficulties. Which is where the seaweed enters into the picture.
Carrageenan comes from red seaweed that makes its home on the rocky shores of both Europe and North America. This seaweed is harvested and dried for the sake of preservation. The carrageenan in the seaweed is extracted through immersion in hot water. After a purification process, the carrageenan is ground into a powder. This powder is then blended into the other ingredients that creates the ice cream to act as the stabilizer. What the stabilizer does is to retard the growth of the ice crystals by forming a layer of protection around them.
And that is what seaweed is doing in your ice cream.