I think it's alcohol and salt... That usually does it. If you're talking about the Professor's Pipe-Sweetening Treatment that is.
GL Pease also has another way of doing that uses activated charcoal (
http://www.glpease.com/Articles/Spot.html). Just don't put anything in the oven that would melt obviously.
Softie bits don't add to the sour taste. Normally, they're tasteless, and the most they would taste like rubber when new.