A week ago, baking this year's Leland Awards cake, because I'd pulled up so many crumbs in the frosting on last year's edition, I decided I may as well (1) crumb-coat (something I've literally never bothered with before), and (2) go a little bit looser with the frosting.

And I noticed that where the recipe from the back of the C&H powdered sugar box normally crusts to some extent, my maple-cinnamon variation (farm-bottled Vermont Grade B replacing most of the milk, and ground cinnamon instead of vanilla extract) wasn't crusting at all.

And thinking back, my strawberry variation (with seedless jam replacing, if I remember right, about half the butter and most of the milk) doesn't crust at all, either.

The crumb-coat, and the somewhat looser frosting, did keep me from ripping up the top crust of the cake, but I'm guessing that it would have been more effective (and I'd have been able to go stiffer with the main coat) if it had crusted.

I'm thinking that the syrup in the maple-cinnamon, and the jam in the strawberry, are making those variations hygroscopic.

Is there something I can do to compensate? To encourage crusting?

Same here. When I use honey, maple syrup, jam, etc in buttercream, it stays soft and sticky. When I must have it crust, I use extract for flavor.

"...Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing material becoming physically "changed" somewhat..."

boy, new word, I had to look it up to understand.

But if you sit out a bowl of granulated sugar it stays dry for a long time.  Although it will eventually attract water to the surface and crust.

A bowl of honey can sit out and stay sticky for a long long time. Can't think how could you make it un-sticky.

Wonder if honey or maple dehydrated crystals would work? or would they just stay rock hard in icing.

Yes, my old boss made an icing she could practically iron the wrinkles out of once it was on the cake. She used Sweetex & butter, sometimes with cream cheese, and powdered sugar, of course. The crumb coat had a bit more sugar, and was tighter than the top coat.  And flavorings came from little bottles, like Lorans, or sometimes the bottles of flavoring used in coffee shops. She also flavored some cakes with a few squirts of a 50/50 mix of simple syrup & Amaretto or Chambord (the 'tastes just like_____!" less expensive version) or some other apertif.  But she guarded her crusting icing recipe, and I've tried a dozen various versions I've found online, and none are so agicelyreeable as hers. Based on taste, I'm guessing she may have used more shortening than I'm willing to use, as I tend to prefer butter and cream cheese to make better tasting icing. But according to Yelp & other online reviews, people didn't like the taste of her products & gave 2-3 (of 5) star reviews,saying cakes were "dry" and icing had "greasy after taste".

So my question is: must we sacrifice taste for incing that cooperates? My best tasting icing looks fine for piped cupcakes and home style cakes, but won't get the fondant smooth look that I know some people get from their "Buttercreams".... that look great but how do they taste?...

I added some Dream Whip powder to my crusting cream cheese icing, which tightened it up a bit, and many people say add cornstarch with your powdered sugar for a tighter product. Many others swear they could eat Indy Debi's icing with a spoon, but it's got more shortening than I care for. 

The syrup & preserves will remain sticky I'm afraid, but can we get an icing without much shortening that smooths out nicely?  Fondant is really pretty but it scares a lot of people....

Despite spending way too much time trying to get this perfectly smooth, I have pits & divits, etc. Look closely and you can see what I mean. It's frustrating!