I've added an update to that post: http://www.jefftk.com/p/citric-acid
I ended up ordering malic and fumaric acids as well. I like the malic acid a lot, but the fumaric acid is really hard to taste. Not being soluble in water it just sits on the tongue being slightly sour. I probably just haven't found the right use for it yet.
The best part of sour patch kids was the white powder left over at the bottom of the wrapper.
I once had a one-pound bag of Sour Skittles, and after eating all of them, consumed the entirety of the white powder left over in the bag at once. Simply thinking about that experience is sufficient to produce a huge burst of saliva.
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