We drink a lot of milk-based drinks, especially in the morning. The first one is usually a 6-ounce traditional cappuccino with lots of floaty foam. We both take a bit of sugar, usually muscovado, sometimes demerara. For years I've put the sugar in the cups and pulled the shot over the sugar...don't know why...perhaps an old habit from years of making Cuban coffee.

Sometimes, I put in some flavouring, usually maple syrup (don't judge me too harshly...I'm Canadian and we put that s**t in everything ). The other day, I put the maple syrup in the milk and foamed it. The QC department pronounced this a superior cup. I noticed when foaming it that the texture of the foam was thicker (no latte art here). Just for fun, the next day I put the sugar in the milk. Similar result, but not quite as "stiff" a foam as with the maple syrup. Again, kudos from the wife. The next day, I want back to putting the sugar in the cup. She-who-must-be-obeyed immediately said, "This does not taste as good as yesterday." This morning, back to sugar in the milk...well, what'ya know one sip and she gave her approval.

So, what does all this mean? I've no idea. Same coffee, same machine, same sugar, slightly different method of combining them all together. Has anyone else messed around with this idea? I did a quick search and turned up nothing.

Try dissolving the sugar in the espresso before adding to the cup. It's interesting that you say your milk with maple was thicker since heat makes sugar more viscous. I will try whipping up some cream tonight with maple instead and see. For science, of course. Mayhap the resinous qualities in the maple syrup are to blame.

I too am prone to adding a bit of sugar to my lattes. Though I usually put it in cup before pouring the shot. I'll try adding it to the milk before frothing instead.

The foaming changes the texture of the milk and stimulates the sugars in it.
If you add the syrup before foaming the milk, I can imagine this happening to the (many) sugars in the syrup too.
And thus adding extra flavour to it.

What seems to make a hit around here is sprinkling a non-dissolving coarse brown sugar (Sugar in the Raw) on top of the drink. This messes with any latte art, but lets you taste the natural sweetness of the milk with a crunchy added sweetness when you take in the top layer. I actually like crema flavored milk, and am guilty of using my index finger to scoop the foam/crema/sugar mix out of the cup after the drunk is gone. My wife yells at me for that.

Been doing this for years (adding sugar to milk prior to steaming). But like Peter (cunim), I have a slight preference for the texture of sugar sprinkled atop the drink.

For iced espresso drinks, I dissolve sugar in hot espresso before pouring over ice.

If the wife wants sugar, I pour simple syrup into the milk before frothing. This is a tip I picked up visiting The Grind Coffee Project in Ft. Lauderdale several years ago.

I keep a small jar of homemade simple syrup on hand for coffee beverages and cocktails. One cup sugar dissolved in one cup boiling water, immediately poured into a small jar (Luxardo maraschino cherry jar works well).

I didn't like adding sugar and having to stir it in after making latte art, so I always add any sugar (pure cane granulated white) to the milk before steaming. It works perfectly fine. When making drinks for others, I always ask their preference before starting.

Maple syrup is an ideal sweetener for espresso. It has a very high sweetness to flavor ratio. Muscovado and brown sugar flavor the coffee. Maple really doesn't.

Liquid sugar (maple) in the bottom of an espresso cup incorporates easily with the oily crema and really knocks the legs off its bitterness. Mixing sugar in afterwards does not have the same effect. Nor does putting sugar in milk. Steamed milk is sweet enough by itself.

I have been putting a dash of sugar in my milk before steaming for over a decade. Tried a lot of variations, sugar in the cup then pull the shot on it, sprinkle on top after preparation, sprinkle and stir, etc. I would inevitably end up with a super sweet blob in the drink which I did not care for. Adding to the milk before steaming fully incorporates the subtle sweetness throughout the drink and does not mess with my pitiful latte art.