Sour = tart = acid = pH < 7 = Net surplus of hydrogen ions in
aqueous solutions (or an equivalent electron arrangement).

Bitter = alkaline = pH > 7 = Net surplus of hydroxide ions in
aqueous solutions (or an equivalent electron arrangement).

Something bitter may also be described as "acrid", but I don't
know whether that term is analogous to "tart". My dictionary
says it means "sharp, bitter, stinging, or irritating to the taste
or smell."

I wonder if I am somewhat less sensitive to bitter taste than
most people. This subject was discussed rather extensively
just a couple of months ago in another thread here in Babbling.
I tasted the skin of a cucumber which I was told was very
bitter and had to be peeled, but didn't really notice any bitter
taste at all. What are some other things I can taste to learn
more about the flavor of "bitter"?

I dislike the smell and taste of coffee, but like chocolate and
"mocha". But that may be sweet chocolate rather than dark.

* * * *
The spelling and meaning of "chili" was also extensively discussed
in that same thread.

* * * *
The shaking of the body one may experience on tasting
something very sour is a shudder, rather than a shiver.

My personal experience is that unlike a cough, hiccough, sneeze,
or shiver, which are almost completely beyond concious control,
a shudder appears to be triggered by thoughts rather than a
physical condition. In that regard it is much like a yawn. I don't
know why a sour taste would make anyone shudder, but it does.

Fear can cause either shivering or shuddering. A shudder is
always brief and violent, while shivering varies in intensity and
duration, depending on the physical stimulus causing it.

-- Jeff, in Minneapolis

__________________
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"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves