Here’s the down and dirty on yeast;
Compressed yeast is fine, it is the standard to which all other yeast types are measured, and it is still the standard of the baking industry, however, it does have its short comings, it must be kept under refrigeration at all times. It has a maximum shelf life of 30-days, but you can see a measurable loss of activity after as few as 7 to 10 days in your cooler. Contrary to popular belief, it doesn’t need to be suspended in the water, it can be simply crumpled right on top of the flour and it will mix in just fine. Active dry yeast (ADY) must be pre hydrated in warm water (100 to 105F) for 10-minutes before you add it to your mix. It has a shelf life of about 6-months for the unopened package, and it doesn’t need to be stored under refrigeration. Once opened, the package should be used within 3 to 5 days. The biggest drawbacks to ADY are the need to pre hydrate (seldom done correctly resulting in loss of yeast activity), and its inherant inconsistency. Remember, this type of yeast was originally intended for use in the home. Lastly, Instant Active Dry Yeast (IDY). This type of yeast is quickly becoming the preferred yeast for many pizzerias. It doesn’t need to be pre hydrated, meaning that with few exceptions, you can just toss it in your mix right on top of the flour and begin mixing. It has a long (1-year or more) shelf life for the unopened package, allowing you to purchase in bulk if need be. It can be stored at ambient temperature, and once a package is opened, it should be used completely within a week (7-days). Leave the IDY in its original bag and just roll the bag down onto the yeast and secure with a rubberband, its that easy. If your total mixing time will be less than 4-minutes, the IDY should be pre hydrated in water at 95F (this is VERY SPECIFIC). Use of a higher or lower temperature water will deleteriously affect the yeast activity.
How much to use:
The conversion is as follows: Compressed yeast (16-ounces) : ADY 8-ounces : IDY 6.5-ounces
Another way to look at it is to find the amount of ADY to use to replace compressed yeast, multiply the amount of compressed yeast by 0.5 and to find the amount of IDY to replace compressed yeast multiply the amount of compressed yeast by 0.4 and to replace ADY with IDY multiply the amount of ADY by 0.8.
Tom Lehmann/The Dough Doctor