Most likely he spat into it. It’s the most logical conclusion to draw from food involved mischief in a Disney movie. It’s never said outright, but this makes the most sense.
However, if you have seen Fight Club you know there is something else that can be done to obnoxious people’s food. And when it is night, I choose to believe that he did something that required a little more concentration.
Can’t you just see the guys in the cast joking about what Crutchy really did to the sauerkraut?