I don't know how many people made homemade ginger beer as a child with that jam jar on the windowsill you threw sugar and ginger at, but I'm trying that approach to keep a permanent fresh yeast culture going.
I started yesterday with 2 teaspoons fresh yeast and 700ml water and a teaspoon of sugar, and a pinch of wine makers yeast nutrient. I took off 320ml today to make bread with and added 320ml water and a teaspoon of sugar back. The plan is to repeat this every day and add the pinch of nutrient every other day. I used a milk frother to evenly disperse the yeast and get some air into the brew before decanting.
Time will tell
Dave