Author Topic: TA to pH  (Read 1072 times)

max1

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TA to pH
« on: August 01, 2012, 02:12:04 PM »
And vice-versa.  Can it be approximately calculated?

Thinking about it, it seems possible to me and I've tried it but can never come up with a plausible result.

TA measures the total amount of acid present in the whey sample at that time and pH is the negative logarithm of the concentration of protons (H+ ions).  So, can we make the approximation that the only acid present is lactic acid?  Then, knowing that the pKa of lactic acid is 3.86 (thus Ka=0.000138), we can calculate the amount of H+ formed by dissociation of the lactic acid then simply calculate -log([H+]) to get the pH.

Here's the equation for the dissociation of lactic acid.

CH3CH(OH)COOH  ----->    CH3CH(OH)COO−   +   H+

Sadly I'm not getting good results doing this.  Any ideas?

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Gürkan Yeniçeri

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Re: TA to pH
« Reply #1 on: August 01, 2012, 04:46:56 PM »
Hi max1,

You seem like more technically minded than me. I asked the same question long ago and the answer was "the conversion is not possible. Stick to one of them and use that only."

But if you create a formula that would be named after your name, I think.

Banjoza

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Re: TA to pH
« Reply #2 on: August 02, 2012, 05:33:35 AM »
Hi Max, I am not good with technical jargon, or even particularly knowlegeable about the subject, but I also wondered about the TA/pH "thing".

Given that the pH number system has already "translated" proton concentration to a simple scale of 0 to 14. Then TA calculation is done using specific chemicals which change colour within a certain acidity or base range specific to that particular chemical. So I would think that the shades between the upper and lower limit of that range COULD be allocated their own pH number. Also if one used various available indicator chemicals right up the range, and allocated those same pH numbers appropriately to every colour shade in every (overlapping) indicator, greater precision and accuracy could be attained too.

Couldn't it?

It all seemed so clear to me when I started to write this... oh dear...

linuxboy

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Re: TA to pH
« Reply #3 on: August 02, 2012, 07:56:59 AM »
Quote
the conversion is not possible.

Yes, it is, but why would you want to convert them? They behave differently (due to other acids present for TA) and require approaching the cheesemake from different perspectives (TA better illustrates concept of buffering capacity, whereas pH is more straightforward in its application).

For an idea of equivalency, please see http://cheeseforum.org/forum/index.php?topic=5816.0

Formula is possible, but too complex for everyday use... trying to systematize cheesemaking to this level often backfires unless one can have very strict controls.
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linuxboy

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Re: TA to pH
« Reply #4 on: August 02, 2012, 07:58:51 AM »
Quote
Also if one used various available indicator chemicals right up the range, and allocated those same pH numbers appropriately to every colour shade in every (overlapping) indicator, greater precision and accuracy could be attained too.

Couldn't it?
Perhaps, but I am missing the point of the mathematical equivalency. Why not just create an ideal chart for the perfect make for each cheese, make a table, and use that during subsequent makes as a quality control measure?
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max1

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Re: TA to pH
« Reply #5 on: August 04, 2012, 04:59:05 PM »
The main reason I wanted to achieve this is for practical reasons.  As a hobbyist, my pH meter is pretty cheap and I find it hard to trust.  I would much prefer using TA, because as long as you're precise in your procedures, titration is fairly accurate.  So I wanted a way to translate the pH targets in recipes into TA.  I guess the best way then is to make do with the pH meter while taking TA measurements at the same time and perfect the recipe over time.

linuxboy

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Re: TA to pH
« Reply #6 on: August 04, 2012, 06:48:07 PM »
That's about best if you are already familiar with your meter. But because TA targets are roughly the same for cheese families, you can switch over and use the TA ranges I posted for the rennet, drain, brine levels and call it done. Which cheese families are you targeting?
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max1

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Re: TA to pH
« Reply #7 on: August 05, 2012, 02:14:37 AM »
Well I'm all set for cheddar, obviously, having worked at Montgomery's.  But I'd like to make some semi-firm washed rind types and Comte.  So both are high drain and high initial pH.  General TA targets for those? Especially drain since everything after that happens fairly quickly.

max1

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Re: TA to pH
« Reply #8 on: August 05, 2012, 02:17:03 AM »
In fact, I remember reading one of your posts where you gave (in pH) a critical tipping point for draining, above which the cheese would retain more calcium phosphate and below which the cheese would be more crumbly.  Do you have equivalents for that in TA?

max1

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Re: TA to pH
« Reply #9 on: August 14, 2012, 10:45:11 AM »
Now that I think about it, another thing making it hard to correlate both would be the buffering capabilities of the curd as the casein micelles absorb protons, right?

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linuxboy

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Re: TA to pH
« Reply #10 on: August 14, 2012, 11:33:51 AM »
Buffering capacity especially accounts for that weird period leading to 6.2 where TA will bounce up and down. So yes.
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