Total acidity vs pH

I’ve been paying more attention to technical sheets as I have tried to get a better understanding of which California cabs I enjoy. One common theme seems to be higher acidity.

I remember the pH scale from chemistry. Most tech sheets also show total acidity, measured in grams per liter.

Can somebody explain how these measures interact? Both in terms of technical/chemistry aspects but also in terms of how we perceive acidity?

Here is a summary of an old paper on this topic: https://wineserver.ucdavis.edu/sites/g/files/dgvnsk2676/files/research-summaries/220%20relationship%20between%20total%20acidity%2C%20TA%2C%20and%20pH%20.pdf

Here is the actual paper: https://ojs.openagrar.de/index.php/VITIS/article/view/6399/6027

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The German concept of comparing the ratio of sugar to acidity may also be an issue to consider, if you are using these analytics for selecting wines.

I think the perception piece of this can be variable from person to person, but here’s my take. Low pH gives me a strong sensation of acidity immediately when the wine enters my mouth. It can be almost too much (and I love high acid wines) as pH approaches 2.0 (correction - 3.0) and below. That sensation passes fairly quickly, though, especially if TA isn’t particularly high. High TA is what makes my mouth water for a long time, giving me a notable perception of acidity throughout the experience, rather than just in the beginning.

One way to learn about your own perceptions is to find some Sherries and Madeiras with similar levels of residual sugar, for which you can also find good tech sheets with both TA and pH. Sherry is one of the few wines that often has both relatively low pH and low-ish (not high, anyway) TA. I think it’s because Palomino is not a high acid grape, and the grapes are so underripe at harvest and then are (typically) acidified, but I’m not really sure. In any case, those comparisons can teach you a lot about how you perceive these differences.

I don’t have a handle on differences between high pH and low TA. I haven’t found comparisons for that like the one above. If anyone has suggestions, particularly of wines with high pH and high TA, please let me know.

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That’s a handy reminder. I’ll paste the pertinent definitions:

Total acidity> : proton equivalence of the amount of organic acid anions present in a wine. It is the number of protons (also called hydrogen ions, or simply H+) that the organic acids (lactic, succinic, citric, acetic, and sulfurous acids) would contain if they were undissociated. It is calculated by measuring the acid anion concentration (by spectrometry or chromatography), expressing them as molar quantities (number of molecules per volume), and then multiplying by the number of protons that would result from complete dissociation.

Titratable acidity> : number of protons recovered during a titration with a strong base to a specified endpoint. It can also be expressed as a molar quantity. Many people use titratable acidity and total acidity as synonyms, but they are not. The titratable acidity is always less than the total acidity, because not all of the hydrogen ions expected from the acids are found during the determination of titratable acidity. However, titratable acidity is easier to measure.

pH> : logarithm of the concentration of free protons, expressed with a positive sign.

You’d need a bit of a chemistry lesson to understand what this all means, which I can do when I have a little time.

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Alan - Can you explain to us laymen the relationship between pH and total acidity?

Love it when WineBerserkers start talking about protons. Maybe we can get neutrons into the discussion as well!!
Tom

Not Alan… but I play him on Dancing With Stars!!! :slight_smile:

There is a weak correlation between T(itrateable) Acidity and pH. Given a wine’s measured TA, it can have a range of pH’s.
What we perceive on the palate as acidity in wine is much more correlated with TA than pH.
I find that many WashState wines have a fair TA but also have a pH on the high side. To me, it gives the wine a sort of a soft/mushy character.
Tom

Another question: when a producer or importer lists TA in a spec sheet are they referring to total acidity or titratable acidity?

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On my lab reports I get Total Acidity and pH. I tend to work mostly off pH in everyday goings and TA and pH are not clearly interconnected.

Some flavonoids and tannins can alter perception of acidity, too. RS remaining as well, of course. A good example are my two Missions. The “Hernan” one with 4 months more of skin contact, will be perceived as having more acidity than the “La Malinche”, despite being harvested on same date. One got pressed off after primary, the other didn’t.

Whole cluster and carbonic tends to increase pH, hence lower acidity, which is why I’ve never really understood why it’s done so much here in CA amongst the cool kids. It makes much more sense to do in a cooler climate. The again, you can make a decent case that for many of the coastal regions in CA, they are in fact in almost a cooler region, so what do I know! [cheers.gif]

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pH is only one factor in deciding whether to do partial or total whole cluster, yes?
Best, jim

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Yes, of course. I’m just personally afraid of stylistic choices that tend to increase pH.

I personally have not found ph increases to be that much with whole cluster fermentations . . .

In Napa and Sonoma Cab and Pinot, either mine or others, it seems almost always that as pH goes up, TA goes down. Enough so that I ignore TA pretty much altogether. And often brix too, for that matter. In Cab once the grapes cross 3.6-3.7 pH, I am usually ready to get off regardless of brix and TA. If I could only see one number to gauge grape maturity, it would be pH. Because I find somehow that all the flavors have developed in Cab by the time pH hits certain levels. Which is one reason I have picked nothing yet in Cab. pH were 3.3-3.5 just ten days ago even with brix at 24.5-25.5, and it just did not taste right for me. The higher brix simply reflected some evaporation due to low humidity and drought all year, not “ripeness,” while pH seems the “truth teller” on real ripeness, for me. I don’t think I have ever once in 17 vintages seen 3.5 pH in Cab and thought it was ready. And I’ve never once seen it over 3.8 and thought it was not ready if not already past ready. There are some winemakers who would consider 3.7 too low and some old timers would say one has missed the boat by that level. It’s all down to taste.

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No, lol. But I’ll give you the background, then try.

First, note that “total acidity” (at least to my knowledge) is a wine term (or, I think, more generically a food science term), not so much a chemistry term. So I’m going by the definitions I read in wine texts, not anything I learned studying chemistry.

I’ll go really basic (haha) to start, for anyone not at all familiar with what “acidity” means in the chemistry sense (apologies to many who do). An acid is any compound that has the ability to release a hydrogen ion (also, and often, called a proton). A hydrogen ion is just a hydrogen atom that’s missing it’s lone electron. The acid molecule that let go of the hydrogen ion hangs on to that electron, and so becomes a negatively charged ion (called an anion). Just to complete the picture, the opposite of an acid is a “base”, meaning a compound that has a greater tendency to grab on to an extra hydrogen ion (and thus become a positively charged ion, a “cation”; which, btw, are the roots of cathode and anode in vacuum tubes). Acids are easy to identify, they usually have the word “acid” associated: acetic acid, hydrochloric acid, tartaric acid, etc. Bases are not typically as easy to identify, they don’t often get the word “base” associated with them. The base most people will know is ammonia. Or hydroxide, as in Sodium Hydroxide. And, of course, the well known first base, second base, and third base.

When you put an acid in water, some of the acid will separate (the chemistry term is dissociate) into a hydrogen ion, and it’s partner anion. How much dissociates is a measure of the strength of the acid. Strong acids dissociate substantially, creating a lot of protons and anions, while weak acids dissociate only a little. Hydrochloric acid is a strong acid, meaning when you dissolve HCl in water, almost all of it dissociates to form H+ and Cl- ions. Acetic acid is a relatively weak acid, meaning it will only dissociate a little bit, so most of it is in the form CH3COOH, with just a small concentration of H+ and CH3COO- ions. That’s why you can pour vinegar on your hands without destroying them, but not hydrochloric acid. Carbonic acid is also weak, so you can spill soda and not get acid burns.

To describe the “acidity” of a solution, we use the concentration of protons. The more dissociated protons floating around, the stronger the acidity of that solution. You could just use the straight concentration, in, say, g/liter to specify acidity (we note the concentration of a species with brackets, in this case [H+], or [H] for short). But because the concentration can range over a very high range of values, from many grams/liter, to micro or nanograms/liter, that’s an awkward way to write numerical values. Instead, we like to use the logarithm of the concentration, which puts the values in the range of small integers. Taking the log of a value is notated with a lower case “p” (which seems unique to chemistry, it’s not a general math expression). Put it all together, and you get the shorthand notation pH, the full definition of which is pH = -log[H]. The negative sign is there because without it, pH would be a negative value for most solutions of acids, and we don’t like having to drag a “-” sign around all the time. So the lower the numerical value of pH, the more acidic the solution is. pH=7 is “neutral”, i.e., the concentration of hydrogen ions in plain water (there are some, water has a tiny tendency to dissociate and form H+ and OH- ions). pH of wine is typically in the 3s. Coca Cola has a pH of about 2.5. Each integer pH step is a factor of 10 in acidity. pH of 0 is quite a strong acid. A negative pH is a very strong acidic solution. pH greater than 7 is lower in acidity than plain water, we call that a “basic” solution, and the way to think about it is that the concentration of the base (the compound with high affinity for protons) is high enough that it scavenges all the lone hydrogen ions, and then takes some more from water molecules, leaving an excess of OH- hydroxide ions. A bottle of household ammonia has a pH of about 12 (I think). Bleach and oven cleaner will be higher, in the range of 13-14, so just as dangerous as a strong acid with pH of 0, just not in the same way. One more subtlety that I won’t go into is that when we talk about concentration, we use the concept of “molarity”, which is a way of expressing the number of atoms, or molecules, or ions per liter of solution, instead of the number of grams per liter - something that should annoy any chemist when it comes to “total acidity”, expressed in g/l.

The pH of a solution depends on how strong the acid (or base) is, how much of it is dissolved, and other factors like temperature, other components in the solution, etc. It’s a very indirect measure of how much of a particular acid is dissolved, not an absolute measure of the total concentration of acid in solution. Which is where Total Acidity comes in. TA is (from what I’m able to determine, I still haven’t found a clean, succinct definition), the total number of hydrogen ions available in the solution (wine, in this case). In some way (most commonly by titration I think, or more accurately by spectroscopy), you determine the absolute concentration of all the acids, and thus the number of protons they have available (some acids are diprotic, meaning they have two available dissociable hydrogen ions, or even triprotic; how “acidic” they are is complicated, and the second proton will be far less “acidic” once the first one is dissociated, but TA doesn’t care about that, it’s just counting them all). Once you have the total number of protons available, from all the acids, you turn that into an “equivalent”, I believe most commonly using tartaric acid as the reference. So you would calculate how many grams of tartaric acid would be needed to supply all the dissociable protons available in the wine, express that in gram/liter, and Bob’s your uncle, that’s TA. I have a hard time intuitively understanding how TA relates to the perception of acidity in a particular wine, but winemakers obviously have developed an empirical understanding of the impact of different TA and pH numbers in wine.

Maybe a winemaker who’s learned this in class will have the exact definition of TA, google has let me down so far finding it.

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Because the different acids in grapes, particularly tartaric and malic, have different strengths the relationship between pH and TA isn’t really linear. Two wines with the same TA, say 6.0 grams per liter, can have very different pHs if one has equal parts tartaric and malic and the other has 75% tartaric and 25% malic.

If I only had one number to pick on, I would join Roy and take pH. But as we’ve managed canopy differently the last 10 years the shift in our typical ratio of tartaric to malic has led me to begin paying a lot more attention to a combination of pH and TA.

Today I learned why pH is called pH. Thank you Alan!

Please correct me if my mental model is off/shitty but I think of pH as the potential for chemical reactions to occur. For example at very high pH there is no free sulphur to prevent oxidation regardless of the TA. On the other hand TA is determines the amount of reacting that can occur. Therefore pH affects taste because it affects the selection of free of chemical compounds (including acids) that might react with your taste buds, and TA affects taste because it determines the intensity of the acid that you’ll taste in a wine. Granted the two are often correlated etc etc

Well, I’m going to bust you a bit and say that’s some pretty creative theorizing :wink:

Any reactions that are pH dependent are only impacted by the pH itself, not the reservoir of total acidity in the wine. Unless the reaction involves the tartaric or malic acid itself, which I think is not common. Microbial stability is dependent on pH, not TA. pH is what determines the state of the wine, TA is a measure of how much potential acidity is there, but not the instantaneous acidity right now.

How the taste is impacted is complicated, because it’s some function of the pH, and the balance of different acids. One thing I didn’t bring up is that every acid has a pKa, which is the measure of how strong an acid it is. Tartaric, malic, lactic, other acids all have different pKa values, and contribute different concentrations of H+ ions to the solution. And the anions themselves have a sensory impact as well (think about how vinegar tastes differently from the acidity of an apple, which is largely malic, or from citric acid in an orange or lemon).

As a former University chemistry researcher, and former high school chemistry teacher, Alan has given a fantastic explanation. I have to admit, that as a chemistry person, I was a bit perplexed by the term “total acidity”. This is not a true chemistry term, but rather something used in food science, likely because so many of the relevant acidic compounds are weak acids. I agree with Alan that the notion of total acidity being measured in units of g/L feels wrong. I realize it’s not “wrong” per se, but really, for a chemist, acidity should be discussed in terms of pH, or at the very least, molarity/molality. But thanks, Alan, really well done.

Incorrect. pH has nothing to do with “potential for chemical reactions to occur”. Not even quite sure what you mean by that, but different reactions happen at different pHs. You mention “very high pH”, which is not going to exist in any kind of wine. All wine is acidic to some degree, which means that, by definition, they have low pH. The pH will affect wine taste all sorts of ways, the presence of free protons themselves create a sour taste, any anions will have their own characteristic flavors, and then the undissociated neutral acid molecules will also have their own flavors. You aren’t entirely wrong when you say “TA is determines the amount of reacting that can occur”, but you’re not entirely right either, and this has “amount of reacting” is not going to have a direct correlation with flavor. One flaw in your reasoning, I think, is that it seems you are somewhat equating acid-base reactions with intensity of flavor. But you don’t need acid-base reactions to occur in order to have flavor. For example, pure sugar or salt has high intensity of flavor, but there aren’t any acid-base reactions occurring. Likewise, the products of the acid-base reaction of vinegar and baking soda, when mixed in equi-molar proportions will produce nothing but a bland tasting aqueous solution of sodium acetate; there’s lots of acid base chemistry happening there, but not lots of flavor intensity.