[This post on spirits acidity was written about five years ago and some how generated a huge amount of google search returns. In the time since, my understanding of the matter has gotten a huge upgrade, but there is still a lot of questions.]
A fairly accessible and historically significant paper on the topic is Studies with Brandy. I. pH by Guymon, Tolbert, and Amerine who were giants in beverage technology. These papers were planned as a series but due to the “exigencies of war” (WWII) only the paper on pH and another on tannin from barrel aging were published. Strangely, these two papers do not appear in any bibliographies that I can remember.
I’ll try and pull some unique things out of the paper and I’ll leave everything I’ve written previously in tact below.
“The pH of seven whiskies varied from 3.68 to 4.78, the highest value being a new whisky.” I think the pH of even the new whisky here is lower than some would think due to a significant amount of volatile fatty acids.
“In rum Valaer (1937) found the pH to vary according to the source, exceeding 5 for Cuban and Puerto Rican rums. The pH of rums distilled in this country was lower.” The pre-Castro cuban rums referenced here have a higher pH because they were relatively more neutral and closer to a vodka. So when we look at these old papers I suspect the pH of new make spirits can say a lot about congener profile.
“The low pH values of young brandies were attributed to the use of distilling material higher in sulphur dioxide. A portion of the sulfur dioxide passing through the still is dissolved in the distillate and is slowly oxidized from sulphurous acid to sulphuric acid. Presumably this is not always the cause of low pH in brandies, for 20 authentic French cognacs, in which the sulfate content owing to oxidation of sulfite is relatively low, the pH was found to vary from 3.76 to 4.98, averaging 4.14.” What they are getting at here is that back in the day a lot of wines intended to be table wines went through the still and because table wines get added sulphur they ended up with a confusingly low pH even though they were probably well rectified and deficient in fatty acids. When a wine is constructed specifically for distillation sulphites are never added.
“pH’s as low as 2.24 and as high as 7.97 were found in certain anomalous samples reported by Valaer in a private communication giving in detail the original data.” This foot note is historically very interesting. Peter Valaer was the great IRS chemist who probably saw and deconstructed more spirits of more types than any ever in the history of beverage science. The foot note shows that the UC Davis guys new Valaer personally beyond just his papers.
“It is therefore evident that the pH of commercial distilled spirits ranges from 4 to 5, that it tends to decrease during ageing, and it appears that rum has a higher average pH than the other distilled spirits.” I think the rums they refer to here are the fairly neutral “dry” rums.
“Some of these abnormally high pH’s are probably due to the distillation of neutralized distilling material and the consequent lack of volatile acids in the distillate.” Neutralizing distilling material with baking soda is practiced by home distillers making spirits from Turbo Yeasts. Often their fermentations get “pricked” and excess acetic acids needs to be neutralized before distillation but at the risk of converting an ammonium salt into volatile ammonia which can corrode the condensor producing a distillate tinged with blue verdigis.
“The buffer capacity of new alcoholic distillates is so low that the addition of only small quantities of either acid or alkaline substances results in abnormally high or low initial pH; for example the use of alkaline water for cutting may result in high pH. Caramel syrups are not stable in alkaline solutions and the brandies with a high pH precipitated most of their caramel as a gummy, reddish mass.” This reference to buffer capacity might be why UV vodka referenced in the original post is proud of their pH neutrality. Cheap vodka might have a lower pH because un-desired fatty acids remain in their distillates. When an old fashioned is batched (guilty!), the sugar probably does not precipitate because the pH is far lower than the fairly pH neutral spirit they are referencing which is basically the brandy equivalent of grape drink.
“Newly distilled brandies with a pH below 4 are also abnormal. Valaer (1939) found a number of the young California brandies of very low pH and, as already mentioned, he explained this on the basis of their high sulfurous-sulfuric acid content.” California used to make sloppy shit! but if you look back at the early days of wine as described by Allan Hickenbothan at Roseworthy in Australia, back in the 1920’s they had a 30% failure rate on wines meant to be table wines and they were all sent to the still. After Hickenbothan discovered the significance of pH and started acidifying wines, what they sent to the still decreased to 5%.
Lately I see the word dry confusingly placed on all sorts of spirits from gin to rum and I don’t really understand what it means. dry is even confusingly used in wine speak. Many people can’t make heads or tales of whether a wine is sweet or not. Is there unfermented sugars or are people referring to levels of acidity? many people think rums are sweet because they are made from sugar but that sugar is transformed into alcohol as well as not-volatile so if rum has sugar it is added post distillation. Well whats the deal?
If like wine, dryness often ends up referring to acidity, what is the acidity of spirits? Should un-aged spirits mostly be the same and there be some difference in aged spirits? is there perceived sweetness due to high extracts in spirits like some times is encountered in wine?
The UV vodka website proudly claims their product is close to pH neutral relative to other budget producers who acidify their product for some spirits tax loophole. This makes really no sense to me but the budget producers would definitely have some dry booze. Could these practices in neutral spirits be born out of some sort of tradition? Should my C.J. Wray dry rum be fairly low in pH? and if it is, would the result be due to additives or stuff naturally going through the still?
Maybe to solve some of the mystery I should calibrate my Hanna Instruments pH pen and have a go at the spirits that are laying around.
Calibrated with fresh solution.
Whole foods distilled water. pH??? Well my distilled water was below 7 which is kind of a bad omen, but maybe acid is attached to my electrode from my cleaning solutions etc? Maybe the temperature is messing with things? Well I put on a new electrode, calibrated it and I still can’t get a 7 out of this distilled water but maybe its is messed up.
C.J. Wray dry rum pH 4.85
Gordon’s dry gin pH 6.90 <— switching back and forth and this rockets back to 6.90 so the pen works?
Myer’s platinum white pH 4.42
Clement VSOP pH 3.78
Back to the calibrators… things check out… more or less… I tried to go back and forth between samples to duplicate my initial numbers. More or less they check out.
Batavia Arrack Van Oosten pH 5.02
Seagram’s Distiller’s Reserve pH 5.13
Trimbach Framboise raspberry brandy pH 6.80
lemon juice pH 2.37 (time for a cocktail!)
So wow, I don’t really have too much confidence in the tester but I think it can still teach something about what we drink. It is strange how drastically different Gordon’s and the Trimbach are from the others. Your choice here would apparently have a large impact on balancing a sour. Are the results here the reason the rum & coke is more popular than the fairly acid neutral UV with coke? Harold Mcgee puts black coffee at pH 5.0 and yogurt at pH 4.5. So are the results here negligible because we pile on the sugar with our mixers or are these pH factors important in shaping consumer preference over the long run?
Now I’m curious how the more mainstream gins that I work with at the bar stack up, and how does all this acidity get there in the first place? any insights?
I haven’t really put things to test on what comes through my still, but now I’m even more curious and I think I’m going to have to test some things… distilled, citric, malic, tartaric, and acetic acids… and it was the last of my bottle, but if I added baking soda to the low pH Clement would it have fizzed? could I neutralize that acidity?
Do some dry gins have more acidity now because the palate needs it in a martini (or maybe not, it is my assumption from loving dry wine) but no one wants to get it from dry vermouth. So does a great marriage of gin and dry vermouth like you see in weird reviews really have to do with finding a most harmonic pH?
Quite a lot of new mixology questions.