Wine must is made from fresh or frozen crushed grapes and contains the skins, seeds, and stems of the fruit. When you purchase frozen grapes, the best-frozen wine must has been destemmed. Destemmed meaning that the grapes have been put through a machine that removes the stems from the fruit. Buy frozen grapes or wine grapes online that have been subject to frozen in this manner. Frozen must is generally good for many years if kept at proper temperatures.