Dunder is the yeast-rich foam leftovers from one batch of rum that is used to start the yeast culture of a second batch. It is the traditional yeast source in Jamaican rum. Similar in process to sour mash in Bourbon whiskey, it is a crucial step in achieving an authentic rum flavor. Dunder contains many by products that help in future fermentation's. These include dead yeast cells that are used as protein. Subsequent fermentation's using dunder must be carefully controlled to prevent stress on the yeast which will cause a greater amount of mutatians. Also if planning to store dunder before use it is advised to refrigerate the dunder to supress cell division as to prevent mutations. These mutations change flavour,alcohol content, and overall effect consistency of the fineshed product. Dunder if not used to re-pitch the yeast colony also can be applied as fertilizer.