Quantity of rapid rise yeast vs regular yeast in bread machine

There is certainly a difference between different yeasts. Different kinds of yeast react differently, are "happy" at different temperature ranges, produce different amounts of gas, live for different amounts of time. In my little world, however, it's better to use a yeast that you use commonly and understand than it is to experiment with a different yeast that may not behave the way you expect.

The thing is "baker's yeast" is a generic term. If it called for rapid rise yeast, and all you had was active dry yeast, I'd say to go out and buy some, or your bread would become flat. Chances are, you have one of those two kinds. They both work in most recipes, but each have their peculiarities, and you need to adjust.

I'd give it a shot, and see how it comes out. If your bread ends up "whacky", then try something else.

First off, it's good to understand the difference between active dry yeast and rapid rise yeast. Active dry yeast is a larger granule of yeast in which the outer shell is composed of mostly dead cells entombing the dormant nougaty goodness inside. It has to be proofed to seperate out all the cells and rehydrate the interior active cells.

Rapid rise yeast is a typically a combination of 2 different strains of yeast (so those with a very discerning palate might be able to tell the difference, I've never really tried). The granules of yeast are smaller and dried slower to preserve more yeast cells. Ascorbic acid is also added to push the yeast into overdrive a little faster.

A great video that helped me a lot is http://how2heroes.com/videos/dessert-and-baked-goods/yeast-101 I have noticed before issues with Rapid Rise yeast not proofing very well the second time around. Apparently it's designed to give you one really good proof and then die out (play hard and die young). Instant yeast however is Rapid Rise yeast without the hardcore party attitude. It's what they use at the King Arthur bakery test kitchen, so that's good enough for me! They say to use them interchangeably, but many other sites I see show a difference of about 20%.

2 Tbsp Active Dry yeast ≈ 1.6 Tbsp Instant Yeast