Yeast for baking at home is normally active dry yeast, rapid rise, or instant. Bread recipes from the 1940’s until the introduction of the other varieties refer to active dry yeast. Older recipes might refer to wet yeast, but it became rare. The differences between active dry yeast and others dry yeasts: the particles of active dry yeast are larger, and coated in dead yeast cells killed in the drying process. Active dry yeast has to activated with hot (not boiling) water. Instant dry yeast grains are smaller. It activates on contact with the water in a recipe, and almost never needs to be activated or prehydrated to propogate. See All About Dried Yeast, What is Bread Machine Yeast, the King Arthur flour Ingredient Guide, the King Arthur web article All About Yeast, and the King Arthur blog post “Which Yeast to Use”. See also Commercial Yeast in Fresh Loaf Baker’s Handbook, and What’s the Difference between Active Dry Yeast and Instant Yeast. For the history of baking yeast, and the ways it has been presented, Lesaffre’s Explore Yeast pages are informative. A leading baking industry paper on instant dry yeast: Lallemande’s Update, Volume 2 # 9.
Industrial formulas were based on weight and baker’s percentage. Recipes for home bakers used volume measurements.
Active dry yeast is measured to the nearest quarter teaspoon in the majority of home baking recipes and many bread machine recipes. Active dry yeast had larger grains. However manufacturing has changed; modern active dry yeast a little finer and more dense. Some home baking books are written with instant dry yeast – by volume.
Instant yeasts, once they activate, ferment and propogate, pick up speed and hit a peak. Some compressed and active dry yeasts have a second peak – home wine makers and home beer makers encounter this with their yeasts which have a vigorous first fermentation and a secondary fermentation. Bakers may time their bulk fermentation and final proof to take advantage of each. I found a graph on SAF Instant dry yeast gas production (with the Cyrillic text and the red line for SAF in the post by Mariana January 2, 2018 in the forum Difference in Yeast Brands). I have not found comparison graphs for other instant dry yeasts.
Some yeasts are called quick-rise/rapid-rise yeast. These names refer to the a way of preparing the product – chemical coating of the individual grains. The varieties of product are tried and coated differently. Commercially, instant dry yeast is diffent than some rapid/quick-rise products. See: Yeast: Dry vs. Rapid-Rise and the thread “Fast Active Fleishmann’s vs. SAF Instant” (about pizza dough). The equivalences are debated in forums like Instant Yeast vs. Fleishmann’s Rapid-Rise.
Some yeasts are labelled as bread machine yeast. The proliferation of types and names arose because manufacturers use different techniques and marketing terms.The manufacturers do not explain how rapid/quick-rise products are made, or how bread machine yeast is different from the rapid/quick-rise products. Bakipan, for instance, says that its “Fast Rising Instant Yeast [is] … cake yeast in a semi-dormant state. The drying process in its manufacture reduces moisture content, giving it a longer shelf life than cake yeast while retaining optimum activity. … Bakipan® Fast Rising Instant Yeast is a fast-acting yeast that can shorten the rise times for traditional baking …” Specifications and methods are not noted on the packaging or published widely – perhaps only for some customers. The manufacturers don’t, according to what home bakers say on the Web, respond to inquiries from home bakers.
Books on artisinal bread baking do not distinguish quick-rise/rapid-rise yeast from instant dry yeast: e.g.: Peter Reinhart, Crust and Crumb (Ten Speed Press, 1998); Peter Reinhart, The Bread Baker’s Apprentice (Ten Speed Press, 2001); Peter Reinhart, Artisan Bread Every Day (Ten Speed Press, 2009); Robert DiMuzio, Bread Baking; An Artisan’s Perspective (Wiley, 2010). Reinhart said that instant dried yeast can be substituted for compressed fresh and active dry yeast for home bread baking – it is good enough for artisanal recipe uses. He came to accept that instant dry yeast should be rehydrated for artisanal breads in Artisan Bread Every Day at p. 13 (although fermentation should be slowed down with refrigeration). The accepted ratio to substitute instant for active dry in oven baking is 1 tsp of instant dry for 1.25 tsp active dry.
Instant dry yeasts , rapid/quick-rise yeasts, and bread machine yeasts vary in some way but are equivalent for bread machines.
Some recipe and baking books suggest letting the yeast and ingredients warm to room temperature. Some sources suggest that keeping yeast cold, including dried yeast, slows it down. Reinhart noted that instant yeast is potent but slow to awake in The Bread Baker’s Apprentice at p. 32. refrigeration preserves the product.
Many bread machine source will say instant dry yeast or bread machine yeast. I use instant dry yeast. Instant dry yeast has smaller grains, coated thinly with chemicals; it is denser. The bakers’ rules of thumb for comparing and converting instant and active dry yeast were 1 tsp of instant is 1.25 active dry, or 3 tsp of instant is 4 tsp of active dry. Some resources say active dry yeast is 2.1 g. per tsp.; others say 2.4 g. Instant dry yeast is 2. 8 g. per teaspoon. If 1 tsp active dry yeast weighs 2.4 grams and 1 tsp instant dry yeast weighs 2.8 grams, the ratio is 6/7. Possibly, there is a difference in the amount of coating in a gram of active vs. a gram of instant, but that is splitting hairs. At the 6/7 ratio for volume: