Why does my reduced stock sauce taste better the next day?

I simmered some roasted vegetables (and tomato paste) with some store bought stock powder and water then added some corn starch to the mix. After the sauce cooled down, it tasted great but over night the sauce became a lot more intense in flavor. What happened and is there a reason for this? Are there some science shenanigans going on? submitted by /u/Punguin456