The key to keeping your Shea butter or mango butter from becoming grainy is to use slow low indirect heat. When the butter is heated too quickly and at a high temperature it will cause the butter to turn grainy. Using the microwave can be a little tricky because it heats unevenly and hot spots can occur. The double boiler option would be a great choice to melt your butter. Heating the butter no higher 175 degrees and no longer than 20 minutes will keep it smooth. I hope that helps.