I’ve mentioned a couple of times here that I often substitute instant yeast for active dry yeast. I didn’t even know what instant yeast was until a year or so ago; I just used whatever was on sale at the supermarket.
Now, however, I make sure to use instant, and here’s why: I get a quicker, better rise from instant yeast, and a lot of the new bread books use instant yeast. Most of the older bread books and cookbooks call for active dry yeast. Luckily, substituting instant yeast for active dry is very easy.
Instant yeast is also sometimes sold as “rapid rise” or “bread machine” yeast. Active dry usually just says “active dry”. The two types of yeast are processed differently, so that it is usually best to dissolve the active dry in water (sometimes called proofing) first while instant yeast can be added directly to the dry ingredients. Some recipes calling specifically for active dry yeast still specifically say to mix the yeast in with the dry ingredients, though.
Instant yeast contains about 25% more living yeast cells per teaspoon than active dry (this is from The Bread Baker’s Apprentice, by Peter Rhineheart).
So, substituting instant yeast in a recipe calling for active dry is a matter of decreasing the amount of yeast used, adding the yeast to the dry ingredients instead of proofing first, and reducing rise times. Bernard Clayton, in The Complete Bread Book, says that rise times are reduced by about half, and I’ve found that to be true.
I do not buy my yeast in packets; it costs too much that way. I used to buy in jars, but now I get it two pounds at a time from Sam’s Club, and store it in the freezer. It is a pet peeve of mine when recipes call for one or two packets of yeast and don’t give a teaspoon amount. Usually one packet = 2 and 1/4 teaspoons of active dry yeast.
When a recipe calls for two packets of yeast, I use a tablespoon of instant yeast (two packets = 4 1/2 tsp of active dry yeast, so a tablespoon is roughly 25% less, without getting too nitpicky). When the recipe calls for one packet of active dry yeast, I use 1 1/2 teaspoons of instant yeast.
Instead of proofing the instant yeast with a small amount of liquid first, put it in with the dry ingredients and add the small amount of liquid in with the rest of the liquid ingredients. If it makes you nervous not to proof (because it also serves the purpose of making sure your yeast is still active and hasn’t expired) just go ahead and proof the instant yeast. I don’t think it hurts anything, it just isn’t strictly necessary.
The main problem I had when I used instant yeast without making any allowances for the differences between it and active dry was in rise time. I would let it rise the entire time the recipe specified, and then my bread would have risen too much (overproofed) and would fall in the oven a little, instead of rising in a last burst of yeast activity (oven spring). If you can’t be bothered to do the math to reduce yeast amounts, at least be aware that the rise time will be significantly shortened.
To substitute active dry yeast for instant, you would do the opposite: increase the yeast amount by about 25%; take 1/4 cup of the water/liquid specified in the recipe and proof the yeast for 5-10 minutes in it before adding to the dry ingredients; and increase rise times to approximately twice those of the instant yeast recipe.