I have never used fresh yeast before because it has to be used pretty quickly. It isn't something that you can store in the cupboard. For the most part I use fast action yeast because as the name suggests, it is quick and easy, not needing to be reconstituted in water. Occasionally, however, I cultivate my own yeast when I want to make sourdough bread. To do this, I add equal parts bread flour with water, and add a few tablespoons of yoghurt. Of course, for soda bread, bicarbonate of soda is used instead of yeast.