Anyone have experience measuring the TA of raw cider with a pH meter?

[Hedo-Rick]

I'm planning on doing some presses of single varietal, heirloom apples this fall and would like to measure and adjust the TA where necessary.

Been doing a lot of searches on TA testing and coming up with a lot of different information. Some say use anywhere from a 5-15ml sample, some say to use 50-100ml distilled water and some say to adjust the pH of the distilled water to 8.2 before testing and others don't say anything about adjusting the pH.

I understand how to use a pH meter, the difference between tartaric and malic acid and the math used to express the result. However, it would be great to get some advice from people who perform TA tests and your thoughts on how you set them up and what I mentioned above.

 

[ajdelange]

I have quite a bit of experience in acidity titration but I don't think I've ever done one on apple juice so I can make some general comments. Total acidity is the amount of alkali that you must supply to a sample of the material being tested to raise its pH to some end point value. That value is arbitrary and to be thorough you should specify the end point pH e.g. acidity(8.3) with the number 8.3 being the most commonly used value as it is the pH at which phenolpthalein changes color. Take 100 mL of juice, insert the pH electrode (properly calibrated) and start adding 0.1 N lye (or some other base of 0.1N strength) from a buret until pH 8.3 is reached. One mL of 0.1 N lye absorbs 0.1 mEq protons and so the alkalinity of a 0.1 L sample which requires x mL 0.1 N lye to reach pH 8.3 has total acidity of x mEq/L. That is really the end of the story but many industries like to express the acidity "as ____ acid" where ____ is the name of the acid that is presumed to be responsible for most of the acidity in the actual sample. WRT to apples that is malic acid. Malic acid has two protons with pK of, respectively, 3.4 and 5.2. At end point pH of 8.3 (3 units larger than the second proton's pK) the acid is completely stripped of both protons. Thus an alkalinity of x mEq/L would be said to have an alkalinity of x/2 millimoles/L as malic acid. That isn't terribly informative and so is multiplied by the molecular weight of the acid. Thus x mEq/L alkalinity is equivalent to x*134.09/2 mg/L as malic acid. Sometimes this is converted to a percentage by weight. A liter of cider weighs SG*998.203 grams. If it contains, effectively, x*134.09/2 mg of malic acid the acidity could be expressed as (x*134.09/2)/(SG*998.203) ppm or that divided by 10,000 as a percentage w/w.

The things that may vary in the cider (or other) industry are the end points used for the titration and the method of reporting the results (mEq/L, ppm, % w/w) and the name of the substance that goes in the "as" phrase. In viticulture acidity is expressed as tartaric acid, in vinegar making, acetic acid and so on.

The size of the sample and the strength of the base used in the titration can also change and are chosen based on the acidity of the sample. Apparently typical cider acidities range from 1 to 15 g/L (1000 - 15000 ppm; 0.1 - 1.5%). That means that 100 mL (0.1L) of sample is going to contain at least 0.1*1*2/134 = 1.5 mEq/L protons and as much as 15 times that. If you do the titration as I suggested above you would use at least 1.5 to as much as 22.4 mL of 0.1 N lye solution. As that is quite a bit at the high end of the range you might , if you think that's how acidic you juice is, want to either
1)Titrate a smaller sample say 0.01 liter (10 mL - dilute it with enough DI water to give you a convenient volume to work with; do not adjust the pH of the dilution water)
2)Titrate with a stronger base: 1 N lye

Either of these options will reduce the mL titrant required by a factor of 10 to .15- 2.24 mL. Obviously you have other volume and strength options as well and should choose based on what you have available to titrate with and the strength of the juice you are titrating.

Final note: If titrating with lye (or any other base for that matter) make sure you have a recently prepared or purchased solution that has been protected from the atmosphere as it absorbs CO2 from the air and loses its strength pretty quickly. Fill the buret and immediately cap the base container. Don't rely on solutions that have been around a long time.

 

[madscientist451]

morewinemaking.com sells a kit for doing this, I don't own one so I can comment oh how good it works:

http://morewinemaking.com/products/vinmetrica-sc200-ph-ta-analyzer-kit.html

 

[ajdelange]

That's for wine which isn't a problem except that the result is expressed 'as tartaric' which isn't much of a problem at all. Tartaric acid is also diprotic with pK's such that it is completely dissociated at pH 8.3 (the manual for this kit suggests 8.2 which is fine as the extra amount of base required to get to 8.3 as opposed to 8.2 is tiny). Simply divide the 'as tartaric' alkalinity by 150.087 to get moles_diprotic_acid/L and then multiply by 134.09 to convert that to grams/L malic.

 

[Hedo-Rick]

That's for wine which isn't a problem except that the result is expressed 'as tartaric' which isn't much of a problem at all. Tartaric acid is also diprotic with pK's such that it is completely dissociated at pH 8.3 (the manual for this kit suggests 8.2 which is fine as the extra amount of base required to get to 8.3 as opposed to 8.2 is tiny). Simply divide the 'as tartaric' alkalinity by 150.087 to get moles_diprotic_acid/L and then multiply by 134.09 to convert that to grams/L malic.

This is basically the route I am going to be taking, but I'm not purchasing an acid titration kit. I need to add a few pieces to my existing equipment and start testing from there.

But just to be clear on a few points you made:

1) do not adjust the pH of the DI water to?
2) diluting a 5-10ml sample in 50-100ml of DI water does not affect the overall TA test? I plan on using .1 NaOH for my tests.
3) even though it's a tiny difference, you suggest a pH of 8.3 over 8.2 for the most accurate results?

 

[RachmaelBenApplebaum]

Out of curiosity, why are you testing the TA of juice for cider in the first place? Are you making acid adjustments prior to fermentation? What is the overall goal outside of just knowing the number?

 

[ajdelange]

1) do not adjust the pH of the DI water to?

No, don't adjust it. You want your lye to react with the acid in the juice, not the water you dilute it with.

2) diluting a 5-10ml sample in 50-100ml of DI water does not affect the overall TA test? I plan on using .1 NaOH for my tests.

That level of dilution is fine depending on the acidity of your juice. Adjust the amount of juice sampled to the amount that has a modest requirement for titrant.

3) even though it's a tiny difference, you suggest a pH of 8.3 over 8.2 for the most accurate results?

No, it simply doesn't matter.

 

[Hedo-Rick]

Ajdelange,

Thank you for the information. Your thoughts put a bunch of questions to rest I had about this process. I'm sure it's going to take some trial and error on my part to understand the process, but I think I have a handle on it.

Out of curiosity, why are you testing the TA of juice for cider in the first place? Are you making acid adjustments prior to fermentation? What is the overall goal outside of just knowing the number?

I am (if need be) going to make my adjustments pre-fermentation. I'm planning on pressing some single varietal, heirloom apples this year that are (for the most part) bitter sweet apples, so the TA will most likely not be sufficiently high enough to yield the results I'm looking for in the finished product. Especially considering I stall the fermentation before it runs dry which doesn't let the acid that is present shine through. So the idea is to manipulate the TA where I want at the start of fermentation so the finished, bottle conditioned cider is bright and fresh and not flabby.

 

[ajdelange]

I'm sure it's going to take some trial and error on my part to understand the process, but I think I have a handle on it.

Any new test you do has something of a learning curve associated with it. Be prepared for a couple of ridiculous results. You'll get the hang of it pretty quickly after a few practice runs.

 

[RachmaelBenApplebaum]

What are you going to use for adjustments? Malic would seem like a natural choice but be aware of pKa etc. You might hit the buffer point unaware and end up with a really high TA and a high pH (super tart cider, microbially unstable, especially with residual sugar). I would say adjust with tartaric since it's stronger and better for lowering pH without such a significant impact on TA that trying to use malic would result in. Good luck in your ventures.

 

[ajdelange]

What are you going to use for adjustments? Malic would seem like a natural choice but be aware of pKa etc. You might hit the buffer point unaware and end up with a really high TA and a high pH (super tart cider, microbially unstable, especially with residual sugar).

I don't follow this at all. If he has TA of 5 g/L and wants 7 g/L then he simply adds 2 g/L malic and he's done. If he gets close to a pK, so what? If, OTOH, he wants a particular pH then he adds acid until he reaches that pH. The fact that he gets close to a pK is a good thing in this event as it makes it easier to hit the desired pH. As the relevant pK of Malic acid (3.40) is within the range of pH's for apple juice I would think that would make it a better candidate as it will buffer closer to the normal pH of apple juice than tartaric would although tartaric is not that much lower at 2.98. Then there is taste which is what this is really all about. Doesn't malic taste more, well, malic than tartaric?

Increased TA from added acid (of whatever type) decreases pH and lower pH is, in beer at least, associated with a more microbiologically stable product. I can't imagine that it would be different with cider.

I would say adjust with tartaric since it's stronger and better for lowering pH without such a significant impact on TA that trying to use malic would result in. Good luck in your ventures.

But manipulating the TA is exactly what he says he wants to do. Given that he has a target or range of TA's as malic in mind and given that adding a gram of malic per liter increases TA by 1 g/L as malic it seems that malic is the clear choice even without considering the flavor impact of using tartaric.

 

[Hedo-Rick]

I don't follow this at all. If he has TA of 5 g/L and wants 7 g/L then he simply adds 2 g/L malic and he's done. Then there is taste which is what this is really all about. Doesn't malic taste more, well, malic than tartaric?

Increased TA from added acid (of whatever type) decreases pH and lower pH is, in beer at least, associated with a more microbiologically stable product. I can't imagine that it would be different with cider.

But manipulating the TA is exactly what he says he wants to do. Given that he has a target or range of TA's as malic in mind and given that adding a gram of malic per liter increases TA by 1 g/L as malic it seems that malic is the clear choice even without considering the flavor impact of using tartaric.

+1

I'm so much interested in the pH as I am the TA. pH deals more with the microbiology of fermentation at the critical point when yeast are going through their lag phase. With that said, I pitch a healthy amount of cultured yeast and have never had a problem with any kind of infection. If I was that concerned with the pre-fermentation pH I would dose my must with Potassium metabisulfite around 50ppm.

To me malic acid would be the only choice for adjusting the TA. I've never used tartaric acid, but a friend of mine who owns and operates a small, urban winery suggested against using tartaric acid for my needs do to it's flavor profile. I am interested however in trying citric acid or a blend of malic and citric to create a different acidity profile.

 

[RachmaelBenApplebaum]

I don't follow this at all. If he has TA of 5 g/L and wants 7 g/L then he simply adds 2 g/L malic and he's done. If he gets close to a pK, so what? If, OTOH, he wants a particular pH then he adds acid until he reaches that pH. The fact that he gets close to a pK is a good thing in this event as it makes it easier to hit the desired pH. As the relevant pK of Malic acid (3.40) is within the range of pH's for apple juice I would think that would make it a better candidate as it will buffer closer to the normal pH of apple juice than tartaric would although tartaric is not that much lower at 2.98. Then there is taste which is what this is really all about. Doesn't malic taste more, well, malic than tartaric?

Increased TA from added acid (of whatever type) decreases pH and lower pH is, in beer at least, associated with a more microbiologically stable product. I can't imagine that it would be different with cider.

But manipulating the TA is exactly what he says he wants to do. Given that he has a target or range of TA's as malic in mind and given that adding a gram of malic per liter increases TA by 1 g/L as malic it seems that malic is the clear choice even without considering the flavor impact of using tartaric.

It's not as simple as that. When you're talking about TA you're talking about the complete acid content of the substance. If you wanted an accurate measurement of malic acid specifically you would have to use spectrophotometry or paper chromatography. What I'm talking about is if you already have a fairly high TA and want to lower the pH you're going to have problems, because malic and tartaric have different pKa's and disassociation constants, tartaric is better for making pH adjustments because it doesn't affect TA as much as something with a higher pKa. Essentially, the higher the TA, the greater the buffer capacity of the substance, and therefore the more resistant it is to pH change via additions of acid. However, if you want to believe that adding acid ALWAYS lowers the pH, feel free. Just inquiring and trying to help. Best of luck.

 

[ajdelange]

It's not as simple as that. When you're talking about TA you're talking about the complete acid content of the substance.

Yes, it is as simple as that and no, you are not talking about the complete acid content of the sample (see below).

If you wanted an accurate measurement of malic acid specifically you would have to use spectrophotometry or paper chromatography.

But you don't. You want the total acidity. Total acidity is not the total amount of malic or lactic or any other kind of acid. It the amount of alkali required to bring the pH of a sample to a reference pH - here I believe it to be 8.3.

Suppose I dissolve 1 gram of malic acid in a liter of water and give it to you with the request that you determine the total alkalinity. The solution pH will be 2.81 and you will have to add 14.91 mEq of strong base to get the liter to pH 8.3. As the equivalent weight of malic acid is 134/2 you conclude that the total acidity of this sample is 14.91*134.09/2 = 999.64 mg/L which is, of course, very close to, but not exactly equal to the amount of malic acid that I put into the liter in the first place.

Now I return to the back room and prepare another sample with 1 gram of malic acid and 302 mg of NaOH dissolved in 1 liter of water to you and request that you determine the TA of this sample. This time you measure the starting pH as 4.3 (more typical of apple juice) but it only takes 14.91 - 7.54=7.37 mEq of base because I already slipped 7.54 meq (302 mg NaOH) into the mix in the back room. You conclude the TA is 7.37*134.09/2 = 494.12 mg/L. This is half the amount of acid I added but is, nevertheless the total acidity of the sample I gave you. Now if you fully understand how this works and the only acid in the sample is malic you will know how to compute the total amount of malic which went into the sample from the 'total' acidity and the pH using the two pK values for malic acid. IOW it appears your confusion stems from your misapprehension that 'total acidity' means the sum of the malic acid, bimalate and malate in the sample IOW the amount of malic acid that someone originally put into distilled water before adjusting pH to whatever pH the sample is presented at. That is not what it means. It means the amount of base that must be added to the sample to get it to pH 8.3.

What I'm talking about is if you already have a fairly high TA and want to lower the pH you're going to have problems, because malic and tartaric have different pKa's and disassociation constants, tartaric is better for making pH adjustments because it doesn't affect TA as much as something with a higher pKa.

I think we covered in the previous post that what OP wants to do is manipulate TA, not pH. Either acid will do to manipulate TA as adding 1 gram of malic increases TA by 1 gram as malic and adding 1 gram of tartaric increases TA by 1*134/150 grams as malic. We don't care about buffering because we are not concerned about pH.

Essentially, the higher the TA, the greater the buffer capacity of the substance, and therefore the more resistant it is to pH change via additions of acid.

We don't care about buffering because we are not concerned about pH in the sense that we want to regulate it to some value. At the same time we (or rather OP) do in the sense that the TA is the buffering of the sample to pH 8.3.

However, if you want to believe that adding acid ALWAYS lowers the pH, feel free.

That's a pretty good thing to believe. Could you cite an example where adding Løwry-Bronsted acid doesn't lower pH?

Just inquiring and trying to help.

We know you are trying to help but apparently you don't understand what 'total acidity' is and so are muddying the waters. That is actually OK since it got a bit more of the science aired here.

 

[WVMJ]

RIck where are you at? I hope you post your results here along with SG of the juice. The thing you need to get around when diluting your sample is that with TA you are measuring the mass of all the acid, so its like if you have 2 pennies, if you have them in 10 mls of water you got 2 pennies, if you put them in 100 liters of water you still have 2 pennies, diluting the sample has no effect on the total acidity of the sample. It does affect pH, the concentration of H when you dilute it. With apple juice being so clear is there some reason a simple titration with phenothalien doesnt appeal to you as its easier, the color transition is easy to see in cider vs like a red wine, all the equipment is the same minus the pH meter. WVMJ

 

[gregbathurst]

The reason for using TA is to measure the acid that you taste (obviously). The complication is that different acids taste quite different, and behave differently. The acids you will meet in cider are mainly malic, lactic, carbonic and acetic. Malic tastes quite different to lactic so just measuring TA when you don't know the balance between malic and lactic is of limited use. Tartaric as in wine also tastes different. Malic is a very sour acid so needs sweetness and fruitiness to balance it. Malic in a dry cider is very noticeable and not so nice, if you want a dry cider you are better to put it through MLF. Lactic acid is much softer and less sour than malic, though it is lactic that gives sourness to beer. If you have malic acid in a cider at room temperature chances are it will go through MLF naturally, so adding malic will probably just mean more lactic at the end and the TA will not be as high as you expect. If you start with juice at 0.5% TA and add 0.2% malic it will initially go to 0.7% TA but probably end up lower around 0.4%. Tartaric is stable so will have a permanent effect on TA. 0.7% will taste quite different depending on the acid involved, 0.7% lactic will taste much less acid than 0.7% malic. The main benefit in measuring TA for cidermaking is so you can build up a level of knowledge about what makes a good cider, and it depends a lot on what you want out of the final product. You can't just say "I want my cider to be 0.7% TA" and expect that will always give you the same cider, it is a lot more complicated than that. As always, the experience of the cidermaker is the most important thing. Remember that malic acid is very unstable biologically.

 

[ajdelange]

I hope you post your results here along with SG of the juice. The thing you need to get around when diluting your sample is that with TA you are measuring the mass of all the acid,

You are not measuring the mass of anything let alone the acid(s). You are measuring the quantity of protons which must be absorbed from the juice to reach the end point pH and then expressing this in terms of the equivalent amount of acid of a particular type that would yield that same quantity of protons to the same end pH. There is actually little malic acid in apple juice. If it's pH is 4.2 (which is, I believe, typical but I'm really visiting here from the Beer parts of this site) only about 12.6% of the total malo is the acid (H2Mal) while the majority, 79.5%, is bimalate (HMal-) and the rest, 8% dimalate (Mal--). While this practice is steeped in tradition in many industries (in the water industry and brewing alkalinity is expressed as calcium carbonate when, in fact, the responsible species is bicarbonate ion) I believe it leads to more confusion than benefit. It leads, for examples, to statements like this quote and is, I believe, responsible for the confusion of RachmaelBenApplebaum. I thus recommend that acidity and alkalinity be expressed in their fundamental units as, respectively, the mEq of acid or base consumed in the titration. But who am I? Just another guy with an opinion.

...so its like if you have 2 pennies, if you have them in 10 mls of water you got 2 pennies, if you put them in 100 liters of water you still have 2 pennies, diluting the sample has no effect on the total acidity of the sample.

For practical purposes this is true but dilution does effect total acidity because water itself has a small total acidity, in fact it would probably be better to call it tiny, to end point pH.

It does affect pH, the concentration of H when you dilute it.

It does so because of water's acidity.

 

[ajdelange]

Double post deleted.

 

[WVMJ]

In the end the results are expressed as gm/L, gm is a mass measurement, I always thought this was the mass of the acids in the must but its really the mass of the acid you want to compare it to such as tartaric or malic? I have to admit to always hating pH meters, never met one I could trust.

 

[ajdelange]

TA as malic acid is mEq/L multiplied by the equivalent weight of malic acid (134/2), nothing more. Obviously that number is arbitrary. We could multiply by 100 and talk about TA 'as calcium carbonate' if we wanted too. We can talk about the acidity of wine must 'as malic' acid if we want to even though with wine the major acid source is tartaric.

So why do we do this? One could think of the creation of juice with a TA of 1 g/L as malic as having been made by adding 1 gram of malic acid to 950 mL of pure water and then adding all the sugars and other flavorings etc. one of which must be a base that will raise the pH to 4.1 or whatever pH the juice has while making up to 1 L. The the 1 gram of malic acid could be thought of as the malic acid that the creator started with when he made the juice. This isn't, of course, how the malic acid gets into the juice. I don't know how that actually happens but I suspect it is thrown off from the Krebs cycle as malate - not malic acid.

Following this line of reasoning a little further we could take a sample of juice at pH 4.1 or so and add acid to it until the pH got down to 1 or so. At that point the juice will contain 1 gram of malic acid per liter assuming, of course, that there was no other acid in it.

This relates to the fact that when you add 1 gram malic acid to a liter of juice that the TA goes up by 1 gram/L. You put the acid in as the acid and malic acid titrated to pH 8.3 yields acidity of 1 gram/gram as malic.

 

[Hedo-Rick]

With apple juice being so clear is there some reason a simple titration with phenothalien doesnt appeal to you as its easier, the color transition is easy to see in cider vs like a red wine, all the equipment is the same minus the pH meter. WVMJ

Because I want to be as accurate as possible and I already have most of the pieces to test the TA in this fashion. I need to add a few things but they are easily attainable. And because I have a pH meter I like, trust and know how to use.

 

[Hedo-Rick]

the reason for using ta is to measure the acid that you taste (obviously). the main benefit in measuring ta for cidermaking is so you can build up a level of knowledge about what makes a good cider, and it depends a lot on what you want out of the final product. you can't just say "i want my cider to be 0.7% ta" and expect that will always give you the same cider, it is a lot more complicated than that. As always, the experience of the cidermaker is the most important.

+1

 

[ajdelange]

...so just measuring TA when you don't know the balance between malic and lactic is of limited use.

If you know what the acids are (e.g. malic and lactic) and if you are fairly certain that there are no other acids besides what is on your list it is possible to estimate the quantities of each from the titration curve for the sample. You need a handful of pH vs added base measurements rather than just the one at pH 8.2 - 8.3. Excel has the power (Solver) to compute estimated concentrations. Is there any interest in this?

 

[beren]

sorry wrong thread :-D