When aging pizza dough in the refrigerator for 1-2 days, I mix the salt and "Saf-Instant Dry Baker's Yeast" (a Japanese brand) with the flour and add room-temperature or cold water. I always get lots of yeast bubbles within hours in the fridge, and lots of rise when par-baking, so I know the yeast is happy.
When I tried making same-day dough, I fell back to habits I learned as a kid, to mix the yeast with water as hot as I could stand my finger in. I mixed salt in that water too, and that was the only time in years of weekly baking I got no rise. Question part 1: Does salt kill the yeast??
Question part 2: Is there any reason to even use hot water if room-temp water works fine with this brand of yeast?
Question part 3: is there any reason not to simply use the mix of dry ingredients that I have success with with refrigerated doughs? If not, why do books/recipes/relatives insist on the hot water dissolve-the-yeast step, which means you have a couple more utensils to wash?
Best Answer
The answer is, as you suspected, you killed your yeast.
If you look at your original description of the process, you add the yeast to flour, along with salt and then add hot water, the flour is presumably room temperature, so it acts as a cooling agent and spreads the heat out so that most of the yeast survives and the final mixture is about body temp (37 C, or 98.6 F), which happens to be about the best temperature for yeast to grow. You do however need a little warmer to activate dried yeast, but this will be only a matter of 40 C/105 F
When you do this with just the yeast and water: You say that you use water that is as hot as your finger can stand. This happens to be about 55-60 C/130-140 F, yeast are killed by water hotter than about 45 C/120 F. To determine the tmperature, do not use your finger, these tend to be less heat sensitive than other body parts, instead drop a little on your wrist, if it feels comfortable, then it is good to go. If it feels hot the water may be too hot.
You can indeed just mix the flour, yeast, salt and add warm water for an instant dough, there is often no need to proof the yeast (this is the water step). The proofing step does lower the risk of your dough not rising because the yeast were inactive though, and then you have wasted ingredients...