I want to try baking bread using fresh yeast which I found in 25g cubes in the fridge on my local supermarket. However, all the recipes I've found call for dry or active-dry yeast. The mesurements are either in teaspoons, or just say, "one packet". How do I substitute using the Real Thing? And in recipes that call for the dry yeast to be added to dry ingredients, should I proof the fresh yeast with some liquid for ten minutes or so before using?