I recently caught the youngest haenyeo (74 years old) from the group working on her own batch of uhmoo gasari 우뭇가사리 to prepare for her family. She was nice of enough to explain how it’s meticulously prepared. 1) The seaweed needs to be fully dried in the sun. 2) The seaweed is soaked and washed thoroughly at least 10 times, or until the red color disappears and the seaweed becomes white. 3) Once white, the seaweed is basically boiled in water until the mixture turns syrup-like. 4) It’s put in a container and refrigerated until becoming jelly-like. There were more steps involved, but that’s the simple version according to her. It’s very similar to muk 묵, a type of jelly side dish popular on the mainland.