What makes Kewpie (Japanese) mayonnaise so different from Hellmann's? According to Amazon, Kewpie mayonnaise contains vegetable oil, egg yolk, vinegar, salt, MSG and spices (no sugar). Hellmann's (which I specify only because it seems like it's the 'canonical' American mayonnaise) contains soybean oil, water, whole eggs &amp; egg yolks, vinegar, salt, sugar, lemon juice, natural flavors and calcium disodium edta.

 

To me, the Kewpie mayonnaise seems sweeter, even though it doesn't contain sugar, and the Hellmann's does contain sugar. But that's not even the big difference to me. Somehow, the Kewpie is just "right" in sushi rolls and for just about every other application from that part of the word that benefits from mayonnaise. Yet, I find Kewpie just awful on a bologna sandwich. How are they so different?

If I make mayonnaise, the list of ingredients will look more like the Kewpie, but taste more like Hellmann's.

What gives?
OK, I did it. The rice vinegar was definitely the biggest difference.  A pinch of MSG (Accent) sealed the deal. I found a recipe on Serious Eats. I tasted after every addition, saving the MSG for last. It wouldn't be as close having skipped anything that I used.

I didn't have real hon-dashi or Japanese mustard, but I had some instant miso soup powder and some Colman's mustard. It was close enough. I also used just rice vinegar, I didn't have any malt vinegar.

I don't have any real Kewpie to do a side by side comparison, but I can tell this is pretty close. It's definitely much closer to Kewpie than Hellmann's.

Everything that has been said here was right.