I have a grandma who does this with her 100yr old sourdough starter. Anyone ever heard of this? She's gonna give me some and want to make sure that feeding with flour and water was affect it.
Maybe the sourdough starter your grandmother has is an Amish Friendship starter, but I am not sure. There are different recipes for the Amish Friendship starter for bread on the web. This is just one of them, if you read down in the link. http://www.momswhothink.com/bread-recipes/amish-friendship-bread.html
That starter does have milk and sugar in it. I used to have an Amish Friendship starter and used it to make some breads, but it has been so many years since I had one. If I recall right the bread did taste good. That kind of starter was passed around to your friends.
Maybe you could ask your grandmother what kind ingredients were used to make the starter.