cooking on shabbat?

Question

would it be permissible to mix hot water from an urn, using a kos sheini, with miso, to make miso soup on shabbat. Miso is a japanese paste made from fermented soybeans, it is similar in texture to Chummus. When you mix it with water it gets much thinner, and perhaps even becomes transparent in color, rather than cloudy. I am only telling you this because I am not sure what makes a difference? Thanks in advance for any time you might spend answering this question. Natan