Yeast primer
One of my favorite subjects is yeast as it applies to baking so It thought I'd start a discussion about it by throwing in some practical uses for different types. This is from memory so pardon me if I make any technical errors.
Yeast is one method of producing leavening in breads. It's job is to reproduce and grow which results in the production of carbon dioxide which when introduced to a gluten structure makes bread more voluminous for a given weight. In other words, it's the engine that causes bread to rise and makes it lighter.
Commercial yeast is basically all essentially the same thing. It just takes on different forms depending on how it's intended to be used. Most commercial yeast is a monoculture, meaning it's only one particular strain of yeast which is commercially viable and efficient in terms of rise times resulting from reproduction. However, when you go to the market you'll typically find many different forms including instant, rapid rise, quickrise, bread machine, active dry, etc. As far as dry packaged yeast goes, the only real difference between all of these things is the size of the individual pellets and the dehydration methods used to produce them.
While instant, rapid rise, quickrise, and bread machine yeast all have their subtle differences, they are all designed for the same basic purpose which is to be used without a proofing stage. In other words, they can be added directly to the recipe without first hydrating in warm water. This works well with most types of basic yeast breads, although certain dense breads have a low hydration level that's not well suited to this type of yeast. The good news is that you can proof these types of yeast in warm water anyway and they still work just as well. So for this reason the only type of commercial yeast I keep on hand is instant yeast as it can be substituted for almost all other applications that require commercial yeast.
Active dry yeast is another form that's widely available and is often called for in recipes, particularly in older heirloom recipes as it was one of the first commercially available forms of yeast. This type must be proofed before use in warm water, which isn't a bad idea anyway if you are unsure about the viability of your yeast. The foaming bubbles you see within a few minutes are "proof" the yeast is working. Just be careful about how hot the water is you use for proofing as temps much above 130F will kill the yeast. Unless specified otherwise in the recipe, I just take about 3/4 cup of 100F water in a bowl with 2 tsp (1 package) of yeast and whisk for a few seconds. You should start to see bubbles shortly afterwards if not immediately.
So how do you substitute one type of yeast for another? Well for the types mentioned, you can pretty safely substitute any one of these for another provided you proof the active dry yeast. Sometimes you'll find substitution charts that specify different volumes for different types. The reality is that volumes really don't matter as I'll explain below.
Yeast readily reproduces itself and while there are limitations to how much and how effective the end result is, for practical uses of commercial yeast there's really no limitation. What this means is that a few grains of yeast will eventually produce the same leavening power as a full package of yeast, given enough time, food (flour), hydration (water), and temperature. Change any one of those variables and you change the amount of leavening produced. That's why volume is a much more important indicator of fermentation than time. If a recipe says your dough is supposed to double or triple in volume, let it go until it does and don't worry too much about prescribed times as these can vary greatly. I like to ferment dough in transparent polycarbonate tubs that have volume markings on the side as it takes much of the guess work out of it.
What this also means is you can vary fermentation times based on how you vary those previously mentioned variables. The easiest way is to vary the amount of yeast. Less yeast means longer fermentation all other things being equal. Longer fermentation times means more flavors are being developed. So how does that work? Within flour there are all sorts of microorganisms which are lying dormant and ready to start reproducing once hydration and sufficient temperature is applied. The types of microorganisms vary mostly by the type of flour you have and how it's processed. Bleached white flour will have vary few microorganisms while whole wheat rye flour will contain an abundance of them.
So another type of yeast which is very different from commercial yeast is natural yeast, commonly referred to as sourdough starter or levain. These types of yeast also contain other microorganisms which also provide flavor and leavening and while not as easy to use and efficient as commercial monoculture yeast, they have the potential to develop a far greater depth of flavor. This type of yeast requires that you develop your culture prior to use. This typically takes about a week of feeding and hydrating to get it going initially and makes use of the microorganisms that are present in the flour that you use to feed the mixture. Basically you just mix equal weights of flour and water together and allow it to ferment in a warm place. After 24 hours you throw out most of the mix and add more flour and water, repeating this process each day until you have a viable culture that can be used to "start" a bread dough. The culture must be fed at certain intervals with more flour and water, but may be kept going indefinitely in this manner. By varying the type of flour used, hydration level, and fermentation times you can develop an infinite variety of flavors.
= new reply since forum marked as read
I am surprised at he number of times someone has asked how to make bread or rolls with yeast.
Gonna book mark this...
At the very least, I hope you love it as much as I do!! (Ret. almost a year ago!!)
I've avoided baking because I live at altitude (over 5000') and yeast acts differently here. Finding recipes that have been adjusted accordingly is a challenge, but doable.
This simple recipe seems foolproof (because I made it with no problems 
) without adjusting the recipe. The only thing I have to watch is how quickly it rises. (Bonus! It's a no-knead recipe.)
https://www.kingarthurflour.com/recipes/english-muffin-toasting-bread-recipe
