Through an invisible process this goo makes bread rise. I got the starter from my mother and she got it from my granny. The goo,a mixture of flour, water and sugar,contains a yeast fungus that feeds on the other ingredients Every time I bake,I use some of the sponge in the dough to make the bread rise. Then I add more flour,water and sugar for the yeast to feed on until the next time I bake. If a sponge is kept from getting too warm or cold,and if it is fed sugar at regular intervals,it can live forever. The story in my family is that once,around 1955,my granny lost her sponge.It starved to death when she went on a trip,and she had to get another one from her neighbor. My family has used that sponge ever since.