the innovative fleischmann brothers came up with the brilliant idea that yeast could be preserved in a dry state for much much longer storage than in its fresh state and over the next several decades, it became the standard. fresh yeast is virtually unavailable these days to the average consumer and difficult to find even in large cities.
in europe and other parts of the globe, this is another story. fresh yeast is still available in many a country and is the standard. when my parents first arrived in north america, they had no clue how to use the dried stuff and looked at it a bit suspiciously. to this day, they still opt for the fresh stuff.
luckily, i am able to procure my own stashes of fresh yeast. i measure it out and freeze it for those times i need it for baking. for a long time, i was always confused about using it in recipes which called for dry yeast (and vice versa). in fact, it became annoying having to sit there and scratch my head figuring it out each time.
so to make things more convenient, i ended up asking around and calculating and came up with the following information on the equivalent amounts for dry and fresh yeast.
WEIGHT BY GRAM OF FRESH YEAST
1/4 oz fresh = 7.09 g
1/2 oz fresh = 14.18 g [1/2 oz when packed, ~ 17 - 19 g = 1 pkg dry yeast]
3/4 oz fresh = 21.26 g
1.0 oz fresh = 28.50 g
DRY AND FRESH YEAST CONVERSIONS
1 pkg dry yeast (standard in N.A.) = 2 1/4 tsp active dry = 0.6 oz fresh yeast [considered 1/2 oz cake]= ~ 17 g - 19 g fresh yeast.
i always use the following easy way to convert recipes:
1 packed tbsp fresh yeast = 2 tsp quick acting ("rapid rise") dry yeast = 2 1/4 tsp active dry (regular) yeast
2 oz cake = 3 pkgs yeast (eg. fleischmann's type)
the standard multiplier for calculating fresh yeast to dry is:
(to multiply) fresh amount "X" 0.4 eg. 1.5 oz fresh X 0.4 = 0.6 oz dry
while there is only one kind of fresh baking yeast, there are several formulations for the dry variety:
regular type ["active dry"]: usually very small balls of yeast; this type of yeast is the standard and often recipes using it require two risings (to increase yeast colonization/amounts - yeast tends to grow exponentionally). must be proved before adding to a recipe with water or liquid at a specific temperature (warm).
active dry is basically fresh yeast which as been dried at a certain temperature; it's outer yeast cells are dead and form a protective shell around its inner live cells (approx. 30%). this is why it must be soaked first in warm water.
quick acting type ["rapid rise"]: different strain of yeast from active dry. granulation of yeast is smaller. contains ascorbic acid to increase loaf volume. this type can be mixed directly into the flour (recommended) or proved beforehand. a little less of it is required as it has a stronger formulation than the active dry. it only requires one rising period in most cases.
this type is dried at a different temperature and more live yeast cells are available making fermentation work faster.
breadmaker type: this is formulated for use in bread-making machines. different strain of yeast from active dry. granulation is small. contains ascorbic acid to increase loaf volume.
instant yeast [european type]: this is like quick acting (rapid rise) yeast. it can be added directly to one's dry ingredients (recommended) and proves upon adding liquids. it is manufactured by companies like SAF and FERMIPAN. it is considered a very good baking yeast with a high percentage of live cells available. it can be proved before using also (though not necessary at all times) and is amenable to proving with either warm liquids or cool ones. the temperature of the liquid will affect the rate of proving.
both instant type and rapid rise are said to work better when mixed with the dry ingredients as opposed to the traditional active dry proving method. this dry-mixing technique works better due to the type of yeast strains of rapid rise and instant. both can still be successfully proved with liquid first however, with the same efficacy.