PH and sour / acid taste I had always thought low pH foods had a noticeable sour (acid) taste, and vice-versa.

But when reading The Bread Builders by Daniel Wing &amp; Allan Scott, on page 54, it says:


  The sour taste of especially sour naturally leavened bread comes more from the total amount of acid in the bread than from the pH of the bread.


After knowing that, someone I know made the following experiment:


  
  Measured the pH of vinegar with a ph-meter.
  Prepared a solution of Spirits of salt with the same pH.
  Drink both.
  


Pure vinegar tastes much more acid than spirits of salt. In fact, the last one has almost no acid taste.

So, it seems my initial thoughts were wrong. Why? Also, what makes we perceive foods as acid tasting?



Update:

After some research (thanks to rumtscho's comment) I have found that taste buds detect the presence of H+ ions (as cited in the Wikipedia article on Gustatory system). 

But still don't know why when drinking Acetic Acid (vinegar) sourness is sensed more than when drinking HCl (Spirits of salt), if both of them are diluted to have the same pH.

Update 2:
After @Wayfaring Stranger's answer it is clair that sour taste is given by anions (and not H+ ions), as written in this question's last update.
There's a bit of trickery going on in the comparison of vinegar (acetic acid) to spirits of salt (hydrochloric acid). Your 5% (0.83 molar) vinegar has a pH of about 2.5.
You need much less of the stronger acid, HCl, to reach that same pH (2.5); in fact only 0.003 molar, a factor of 277 less.
Since you taste the anion (acetate or chloride), not the proton (H+), it's no wonder that the vinegar is much more flavorful; there's a 277 fold difference in the concentration of the flavor agent. Pick a different acid, and you'll get a different tasting anion, and a different concentration needed to reach pH 2.5.



Response to comment on taste of anions:

Your linked Wikipedia article gives the impression that the taste reception system is fairly simple, and well understood. It is neither.

Here are a couple examples of reasonably current research on the taste of anions:

The Anion Paradox in Sodium Taste Reception

Anion size of sodium salts and simple taste reaction times.

Take a look at Wikipedia's article on taste receptors. you'll see that 'bitter' tastes are subclassified by 30 or more different receptors.
Salty taste receptors (specific anion and cation) are still are poorly characterized

Research on humans is hard, so it'll probably be decades before the mechanisms of tasting are fully sorted out. Until then, consider sources like Wikipedia expositions of the current state of knowledge, rather than the final word.