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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 & 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:

  1. Measured the pH of vinegar with a ph-meter.
  2. Prepared a solution of Spirits of salt with the same pH.
  3. 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.

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I've found this link on acids at Your Mother Was a Chemist interesting, but not answering the question. –  J.A.I.L. Nov 26 '12 at 12:15
    
The whole paragraph (which can be reached following the link to The Bread Builders book) explains it in more detail. I only copied the first part of the 20 lines paragraph in order not to lenghen unnecesarily the question. –  J.A.I.L. Nov 26 '12 at 12:29
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See also my answer to another question, cooking.stackexchange.com/a/24740/4638, and Aaronut's answer to yet a different acidity vs sourness question, cooking.stackexchange.com/a/17403/4638 –  rumtscho Nov 26 '12 at 16:19
    
@rumtscho thank you. I hadn't seen those questions when I was searching for answers before writing this question. Those might explain why sourdough doesn't taste so sour (if we suppose saliva's enzymes make sugars fast enough in our mouths), albeit the author states it's the buffer effect of the flour's ashes what makes so. –  J.A.I.L. Nov 26 '12 at 19:32
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Does someone know why this question would have been downvoted? Knowing so would help me (and others) improve this (and others) questions. –  J.A.I.L. Nov 28 '12 at 15:25
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2 Answers 2

up vote 5 down vote accepted

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.

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your answer is what I was looking for. But where can I find references stating the taste is given by the anion, not the proton (H+). As I understand, this says the opposite. –  J.A.I.L. Nov 27 '12 at 8:25
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We have sensors (buds) on our tongues and noses to detect compounds, these sensors send signals to the brain that are interpreted as taste and smell. I include smell in this answer even though you are asking about taste because smell is a huge component in taste, which is demonstrated every time you get a cold. These sensors detect specific flavors in foods, but not every flavor or odor has a sensor that detects it. Humans have learned what they can taste and what they can't, which is why we cook with vinegar and not spirits of salt. It may be possible that what we detect as sour has nothing to do with acidity at all, but the taste of the compounds that come along with the acids we eat.

I'm not sure exactly what the authors meant by total amount of acid rather than the PH. My guess is that the microbes that make the dough sour produce a wide variety of acids and flavor compounds that stimulate your flavor and odor sensors in a broad way, making the flavor and odor more intense.

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Acording to acid vs PH, I think Daniel Wing means a dough with low PH releases acid ions a<sub>H<sup>+</sup></sub> very easily. But another dough might have lots of acid ions not released, so the PH would be high, and be noticed as acid by our taste. I'm not very sure of that, that's why I'm asking. –  J.A.I.L. Nov 26 '12 at 11:59
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