Hello Kenn-ga, and thanks for an interesting question.
No, you are not alone. The phenomenon you are describing is
well-known, and is usually called "taste adaptation" -- the fact that
the initial "shock" to the taste buds of a sour (or sweet, or any
other) taste is quickly attenuated as the cells in the taste buds
approach saturation of the chemicals causing the taste, and no longer
fire as rapidly.
A few sites that discuss taste adaptation are:
First sip = a shock to the mouth (compared to second, third sips,
Adaptation = decrease in response under conditions of constant
easily observed with stable stimulus (spatial control, no temp or
has decaying exponential and inverse recovery, period of minutes
After adaptation to different tastants, water takes on various tastes
Sequential effects and rinsing are influential!
Physiological Psychology of Taste
University at Buffalo
Chemical Senses II - Taste Flavor
Taste - A brief tutorial
And some experimental results on the different adaption rates for
sweet and sour tastes:
Taste adaptation, a gradual decline of taste intensity with prolonged
stimulation, is frequently observed in laboratory experiments.
However, during normal eating the taste of food does not seem to
decrease or disappear. We studied whether taste adaptation occurs when
subjects eat yogurt, sweetened with two concentrations sucrose (3.75
and 7.5%). During 90s subjects could eat as much yogurt as they
wanted, and judged the taste intensity at 5, 35 and 95s. In addition,
we examined whether taste adaptation measured with a filter paper
method is related to taste adaptation when eating yogurt.
During the eating of yogurt, sweetness intensity declined with time,
whereas sourness intensity did not. This may be due to a higher rate
of recovery from sourness adaptation. In addition, release from
mixture suppression may have completely counteracted sourness
adaptation, whereas the effect of release from sweetness suppression
may be smaller than the effect of adaptation to sweetness.
Hope this is helpful, but if you need any additional information, just
post a Request for Clarification, and let me know.