Why, when you suck on one of those after dinner, round, candy cane
striped peppermints, does it not dissolve smoothly and evenly, but instead gets
those holes all over and though it?

samvega...

I just wanted to report that I spent quite some time researching
this, and have come to the conclusion that this very important
topic has somehow escaped either the investigatory talents of
the great minds of this planet, or the reporting skills of the
ever increasing ranks of the authors of web documents.

While this represents a travesty of the highest order, still
have I hope that, by having recorded your plea for knowledge
here, on the hallowed pages of Google Answers, it may yet
attract the attention it so truly deserves.

It may assist you or others on this honorable quest to know that
the foundation for these types of candies is called fondant, as
evidenced by this detailed page at Baking911.com:

"Fondant for candymaking forms the basic foundation of after-dinner
 mints, peppermint patties and chocolate-covered cherries. Candy
 corn, seen most during the Halloween season, is a common Fondant
 candy."
http://www.baking911.com/candy_fondant.htm

While my personal experience with the phenomena is limited to
memories from some time ago, I would venture a guess that it
has to do with solid sugar crystals embedded in the fondant,
which dissolve more quickly than the fondant itself, leaving
cavities in the candy instead of in your teeth (if one were
given to conspiracy theories, one could even postulate that
these candies were designed by dentists in the course of 
seeking vengeance on the candies which have wrought such an
overwhelming amount of tooth decay).

The truth is out there.

Excelsior!

sublime1-ga

If you break a peppermint candy in half and look closely at the broken
edge, you'll notice that the candy is somewhat porous. Rather than
being a solid, glassy lump, it is honeycombed with tiny holes of
different sizes. The holes represent little air bubbles that were
present in the candy as it hardened.

It is my speculation that, if the size and distribution of the holes
is irregular (as is almost always the case), the candy will dissolve
unevenly.

pinkfreud, I suspect you are right and have answered my question. I
shall acquire and dissect a dinner mint ASAP to confirm. Thank you so
much for helping me with the nagging question I have had for so long,
that seemed nearly unanswerable. Sublime, I appreciate both your time
researching the topic, and the humor of your comment. I laughed. :)

As a follow-up, I just happened to have one in my car from a recent
trip to Sonic which I have unwrapped and promptly bit in half. It
revealed the innerds of the mint to be smooth and glossy, with no
traces or air pockets or pores. Tomorrow I will pick another one up
and run my water facet on it to see if it produced the same results as
would happen if it were dissolved in someones mouth. It remains
unanswered.

If I can find any confirmation of my theory, I'll be glad to post an
answer for you. There seems to be a scarcity of peppermintarian
hypothesizing on the Web. ;-)

If you have ever watched them make this candy it would be very apparent to you.

Basically, the fondant is a hot, but cooling solution of sugar and a
small amount of liquid(water).  Ordinarily, sugar would crystalize
into a nice solid rock, but in the preparation of fondants like candy
canes and the like, the cooling gloopy mass of sugar is stretched and
pulled as it solidifies.  This is what creates the fibrous ribbon like
appearance that you see in candy canes. The red color is basically
created by adding coloring agents to one fondant, allowing it to cool
with stretching and kneeding.  When it gets cool enough to combine and
not bleed into the adjacent color, it is twisted with another color
fondant to make the red and white pattern.

The important thing to remember is that the candy is not allowed to
become crystalline sucrose.  Thus the candy does not have perfect
crystaline structure. As such, the activation energy associated with
dissolving(or unpacking the solid state) is different depending on the
underlying solid structure.  As such, it will dissolve at a different
rate.

Now if one did not pull stretch and kneed the fondant and just allowed
it to cool and solify, it would likely be more homogenous, and would
dissolve more uniformly, like a butterscotch.

As the fondant is pulled it is also kneeded.  That is, it is doubled
over and then re-pulled.  This process likely introduces the air
bubbles that pinkfreud has mentioned.

Chugs,
Bob