the red tool is a seed, actually. i was planning to put farming some crops in the game to add to the soup as special ingredients but i couldn't get to it in time :-(
the sweetest ingredient is a Candy Corn, but it's a bit more rare to find than the others. there are other ingredients that add sweet, but not as much, and each ingredients both adds and subtracts from the balance. so a candy corn might add a lot of sweetness, but that cuts down the salty, etc.