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Kappa carrageenan can be used to create firm, brittle gels and is especially effective at gelling dairy-based liquids. To gel, the liquid must contain either calcium or potassium that is free to bind with the kappa carrageenan. If the liquid contains both calcium and potassium, that's fine also. If the base ingredient lacks calcium it can be added in the form of calcium salts like calcium lactate or calcium chloride or potassium salts like potassium citrate or potassium phosphate. For ease we will focus on dairy gels.
Kappa carrageenan can also be combined with locust bean gum to strengthen the gels and make them less elastic.
We usually recommend ModernistPantry.com, they have great service and are really good to work with (because of this, we do have an affiliate relationship with them). They also have the Texturas brand, if you prefer that. We also like purchasing kappa carrageenan from WillPowder and get larger quantities and bundles at ForTheGourmet.com.
The amount of kappa carrageenan you use is dependent on the type of liquid you are gelling, and the firmness of the gel you are trying to create. For typical dairy gels you can use a 0.3% to 1.5% ratio. If you are adding locust bean gum, it will be at two thirds the weight of the kappa carrageenan.
In order for kappa carrageenan to be used effectively it has to be properly dispersed and hydrated.
Kappa carrageenan is best dispersed in cool liquids. This will prevent hydration until the liquid is heated. An immersion blender or standing blender is the preferred tool to disperse the kappa carrageenan.
In order for kappa carrageenan to hydrate properly it has to be brought above 70°C / 158°F. Kappa carrageenan does not hydrate well with sugar and so sugar should be added after the hydration process is completed.
To make a gel you combine the kappa carrageenan with the liquid you would like to gel. If the liquid does not have either calcium or potassium then at least one of them will need to be added.
Heat the mixture to above 70°C / 158°F and as high as a boil, then pour the liquid into molds. It will begin to set around 35-60°C / 95-140°F, depending on the calcium and potassium content of the liquid. Let it cool to room temperature or in an ice bath, and then place the gel in the refrigerator to finish setting. It should be fully set after a few hours for most mold sizes.
Once it has set, the gel can be turned out, shaped, and plated. The gel will maintain its form as long as it stays cooler than 10-20°C / 18-36°F above its setting temperature. Please be careful serving gels that are at such a high temperature they can cause severe burns; many people expect them to be cool.The gel will also last for a day or two in the refrigerator.