Have you found a good sugar grinder that lasts?
Numerous times, when my grinder breaks, I just put the coarse sugar into the melanger. And at first I noticed the chocolate seemed to get smoother, quicker than when I ground the sugar first. I thought it was a fluke. But it just happened again last night—after 10 hours with coarse sugar the stuff was as smooth as it could possibly be.
So here is my hypothesis: when you grind sugar first you get a powder that is probably somewhere between 60 and 100 microns, but many more individual pieces than you started with. And these may or may not get caught under the wheel, and may not even get crushed unless they hit it just right. On the other hand, with coarse sugar you have far fewer individual particles that are larger, and when one of them goes under the wheel it pulverizes. Producing a finer grain size than if it had been put through a spice grinder.
So many levels to this question. Where to start? From the top down is good.
Yes, I have a grinder I like. It is the Panasonic Grinder.
But. Just like the description says, I don’t recommend it for grinding your sugar IF your goal is to reduce refining times. But I love it for Brewing cocoa and making my own Masala and curry pasts. In short, I have noticed the same thing you have and have stopped actively recommending people pre-grind any of their ingredients (whole coffee might be the exception). Your hypothesis is as good as any. But I will add in that I think the sugar, being actually rather hard, is acting as a kind of abrasive and is both self-milling down and helping to refine the cocoa particles in the chocolate. And the larger the better.
The other observation I have made is in regard to melanger speed. My experience has shown that if you put in finer, pre-ground sugar and cocoa it actually makes the mixture thicker and consequently slows down the melanger and thus your refining time. Somehow letting it grind down the larger particles keeps things moving along nicely. So, whether any of those theories are actually correct or it is some combination of all three, the result is that I no longer recommend pre-grinding any of your ingredients. Yes I used to, but I’ve tried to edit those out and if you come across them, please feel free to point them out and I will change them. We don’t want contradictions.