Yesterday I made mashed potatoes and they were really good, however I constantly try to improve and I like to understand the various techniques that are being used. One thing that I don't fully grasp is that on one hand, I know that using a food processor to puree the potatoes is a big no-no because it somehow turns the starch into sugar and in the end you get a sweet gooey sticky mess instead of light fluffy mash. Got it. I use a food mill. But on the other hand, I see Chefs "work" the mashed potatoes in a pan for 5mn or more before adding the butter. I understand that you have to dry the potatoes, and that working them like that gives them a smoother texture... but when I see videos of Robuchon really whipping the potatoes very hard for 5mn non-stop like his life depends on it, I'm left wondering: Isn't that action also turning starch into sugar? As far as my experience, it doesn't seem like it does (my mash has a better texture when I work it hard for 5mn over low fire before adding the butter) - but I don't understand why.