To extract the carrageenan from red seaweeds, the seaweeds need to be cooked in water. 

You can put the seaweed in a Victoria’s Secret mesh laundry bag for delicates (or the equivalent, such as jelly bags) for ease in re-steeping and removing more and more gel. 

Another option is to put the seaweed in the pot of water directly and press it through a mesh strainer before use. 

Combine 1/2 ounce of red seaweed (Gigartina/Mastocarpus, Iridaea, Irish Moss) with 1-2 quarts of water in crock pot or pot.

Bring to boil and simmer for ½ to 4 hours on the stove or 8-12 hours on low in a crock pot. 

Occasionally stir or pump the gel out of the seaweed to enhance extraction. 

The same red seaweed used in the first steep can be re-used in 4-5 more batches of water for additional gel extraction.

The nutrients in red seaweeds feed bacteria even at temperatures near freezing, so keep gel refrigerated AND re-sterilize it by bringing it to a boil every day or every other day.

In addition to its own medicinal properties, red seaweed gel is a great medium for medicine making with some of our favorite land plants. I like to extract anti-infective herbs in red seaweed gels for extra potentcy and sticking power for throat and intestinal infections. Traditionally in many countries, a delicious drink is made with red seaweed gel and aromatic spices, such as cinnamon and nutmeg (and whiskey for the Irish!). Red seaweed gel can also be used as an egg replacement in vegan baking, and to add texture to many other culinary delights!

Seaweed mucopolysccharides can be complicated to work with in the kitchen, especially when using whole seaweeds (not isolated hydrocolloids). Kitchen Alchemy has a lot of great blog entries and videos about working with hydrocolloids (carrageenan, alginate, agar) to create gels. They work with isolated mucopolysaccharides, but some of this information can be applied to whole-form seaweed gel extraction and use.