What is the pH of Whiskey?
Q: “Do whiskeys have different pHs?”
A: Yes!
But I’ll be honest, I had never asked myself this question. I just assumed that the pH of all whiskey must be similar and any differences would be insignificant. So I went to Google to get the scoop. And it turns out that not a lot of people talk about this subject. I found two scientific papers that investigated the pH of whiskeys… they were from 1936 and 1942. Both papers showed that aging had direct correlation to a decrease in pH! How neat is that! And I found a whiskey forum discussing pH in distilled spirits. In the forum a couple of people posted the pHs from some whiskies they had at home and confirmed they observed a correlation between pH and age. So let’s quickly dive into the data!
To make sure we’re all on the same page, pH is essentially a scale from 0-14 of how acidic or basic/alkaline a solution is with water being neutral (pH = 7). Some examples of household items that are acidic are lemon juice (pH = 2) and black coffee (pH = 5) and basic are hand soap (pH = 10) and bleach (pH = 12). Whiskey is composed of mostly ethanol (pH = 7.33) and water. But there are also some small quantities of flavor/aroma compounds that impact the pH. Carboxylic acids (like acetic acid) have an impact on a whiskey's pH and are produced by yeast during fermentation and extracted from the barrel wood during aging. Phenols are also slightly acidic and are extracted from the barrel as well. So we can clearly see based off of the compounds coming from the wood that aging would decrease the pH. But the question is, by how much?
The paper published in 1942 showed that the pH of Scotch ranged from 4-4.78 (4.34 avg), “American style Scotch” ranged from 4-6.22 (4.81 avg) and Irish whiskey ranged from 4.25-5.06 (4.55 avg). The ages of these whiskies weren’t specified, however, they did observe that brandy’s pH decreased from about 5.4 to 4.0 within a few years. If we move over to the pHs posted in the whiskey forum, we can see a similar trend. 10 year old Laphroaig had a pH of 3.94, 12 year old Caol Ila and Chivas Regal had pHs of 4.10 and 4.05, respectively, 15 year old Bowmore’s pH was 3.94 and 21 year old Glenfiddich’s pH was 3.64.
This sample set is relatively small and limited to Scotch, so I decided to get a pH meter and take my own measurements. The results are below, but I’d like you to keep in mind that this pH meter was very cheap and I’m not confident in the accuracy of these measurements. Nevertheless, let’s take a look at the results!
| Brand | Age (yr) | Type (country) | pH |
|---|---|---|---|
| High West Silver | 0 | Oat Whiskey (Am) | 7.7 |
| Koval | 0 | Rye Whiskey (Am) | 7.4 |
| FEW Flamming Lips Brainville | 1 | Rye Whiskey (Am) | 4.04 |
| Starward | 2 | Wheat & Malt Whisky (Aus) | 3.39 |
| Starward | 2 | Single Malt Whisky (Aus) | 3.59 |
| Old Portrero | 2.5 | Rye Whiskey (Am) | 3.54 |
| Octomore 10.4 | 3 | Single Malt Whisky (Scot) | 3.9 |
| Starward | 3 | Single Malt Whisky (Aus) | 3.87 |
| Driftless Glen SB | 3.67 | Rye Whiskey (Am) | 3.93 |
| WhistlePig PiggyBack | 6 | Rye Whiskey (Am) | 3.9 |
| Evan Williams SB | 7.75 | Bourbon Whiskey (Am) | 3.65 |
| Knob Creek SB | 9 | Bourbon Whiskey (Am) | 3.94 |
| Masterson's | 10 | Barley Whisky (Can) | 3.92 |
| Russel's Reserve | 10 | Bourbon Whiskey (Am) | 3.9 |
| Laphroaig | 10 | Single Malt Whisky (Scot) | 3.83 |
| Glenmorangie | 10 | Single Malt Whisky (Scot) | 3.91 |
| Ardbeg | 10 | Single Malt Whisky (Scot) | 3.98 |
| Elijah Craig Barrel Proof | 12 | Bourbon Whiskey (Am) | 3.74 |
| Bunnahabhain | 12 | Single Malt Whisky (Scot) | 3.61 |
| Bowmore | 12 | Single Malt Whisky (Scot) | 3.56 |
| The Glenlevit | 12 | Single Malt Whisky (Scot) | 3.67 |
| Red Breast | 12 | Single Pot Still Whiskey (Ire) | 3.58 |
| anCnoc | 12 | Single Malt Whisky (Scot) | 3.79 |
| Caol Ila | 12 | Single Malt Whisky (Scot) | 3.81 |
| The Balvenie DoubleWood | 12 | Single Malt Whisky (Scot) | 3.74 |
| The Balvenie Am Oak | 12 | Single Malt Whisky (Scot) | 3.69 |
| The Balvenie TripleCask | 12 | Single Malt Whisky (Scot) | 3.64 |
| Craigellachie | 13 | Single Malt Whisky (Scot) | 3.85 |
| The Blavenie Carribean | 14 | Single Malt Whisky (Scot) | 3.63 |
| The Blavenie Peat Week | 14 | Single Malt Whisky (Scot) | 3.9 |
| Red Spot | 15 | Single Malt Whisky (Scot) | 3.65 |
| Springbank Rum Cask | 15 | Single Malt Whisky (Scot) | 3.98 |
| Bowmore | 15 | Single Malt Whisky (Scot) | 3.68 |
| The Balvenie TripleCask | 16 | Single Malt Whisky (Scot) | 3.62 |
| Aberlour | 16 | Single Malt Whisky (Scot) | 3.64 |
| Kininvie 1996 | 17 | Single Malt Whisky (Scot) | 3.68 |
| Alexander Murray 1997 Linkwood | 19 | Single Malt Whisky (Scot) | 3.84 |
| The Balvenie PortWood | 21 | Single Malt Whisky (Scot) | 3.75 |
| Bruichladdich Black Art 1992 | 24 | Single Malt Whisky (Scot) | 3.54 |
| TWA 1982 Caol Ila Rum finished | 27 | Single Malt Whisky (Scot) | 3.65 |
In case you’re a visual learner (like yours truly), I’ve plotted these pH values as a function of the whiskey age statement below. Note: I did not include the two unaged whiskeys, which had much higher pHs relative to the aged whiskeys.
Whiskey pH as a function of age statement (not including the two unaged whiskeys listed in the table above).
Looking at this chart, we can maybe extrapolate some trends, but we would really be grasping at straws. As I mentioned above, generally whiskey pH decreases with age due to the organic acids and phenols extracted from the cask over time. This means pH is dependent on the type of cask used for aging and also the age of the whiskeys that were blended into the batch. Keep in mind, the age statement on a bottle indicates the youngest whiskey that went into the batch blend but doesn’t give us any idea about the actual age range of the batch (If my measurements above were all taken from single barrel batches, then that would be another story).
Also, this means that the type of oak, type of wood treatment, size of the cask, and number of times the cask has been used all will impact the whiskey pH. Not to mention, so will the barrel entry proof and maturation environment. For example, in 1959 C. S. Boruff and A. Rittschof published “Effects of Barreling Proof on the Aging of American Whiskeys” in Agricultural Food and Chemistry. They showed that the total acids extracted (acetic acid) increased with lower barrel entry proof.
So yeah… that’s a lot of variables to account for, meaning pH is not only dependent on age. But I wanted to see if I could group the data in a way that minimized those variables to perhaps bring out some trends, so I started with grouping together all of the American whiskeys. I did this because, for the most part, American whiskeys are aged in new, charred American oak barrels (53 gal).
Whiskey pH as a function of age statement for the American whiskeys listed in the table above (again, excluding the unaged whiskeys).
I included a trend line in the above chart just for fun. As you can see there is the gentlest trend downward indicating pH decreases (barely) with age, however, the coefficient of determination (R-squared) is so low that this trend line holds no weight at all. Of the 8 American whiskeys listed here, half of them are bourbons made in Kentucky, so we can assume similar maturation conditions and a barrel entry proof of 62.5% ABV (I believe that is the barrel entry proof of each of these distilleries). The other half are ryes made all around the US.
One of those ryes is Old Potrero’s 18th century rye whiskey, which is aged in toasted American oak barrels rather than charred. Interestingly, it happens to be the American whiskey with the lowest pH out of this group. Could this be that more organic acids (like acetic acid) are extracted from toasted versus charred barrels? Maybe. Could it be that Anchor Distilling uses smaller casks and therefore there are more organic acids extracted per volume of spirit? Not sure. Could it be that the use of malted rye and pot distillation resulted in higher amounts of organic acids in the white spirit already going into the barrel? That sounds plausible. Most likely, it’s a combination of a lot of things including many I’m not even thinking of!
Next, I wanted to see what would happen if age statement was held constant and luckily for me, I sampled a decent amount of 12 year old whiskeys.
pH of various 12 year old whiskeys as a function of brand (organized by increasing pH).
In this chart, you can see that the pH of these 12 year old whiskeys (mostly single malt scotches) ranges from 3.56 to 3.81. Could these fluctuations be within the error of my pH meter? Maybe, but let’s assume they’re accurate. Bowmore, anCnoc, and Caol Ila are all aged in ex-bourbon casks, whereas RedBreast, Bunnahabhain, and all three of The Balvenie whiskies are aged in a combination of ex-bourbon and ex-sherry casks. I was hoping that these whiskies would magically group together so I could conclude “ah hah! Ex-bourbon casks cause the pH to decrease more than they do in a combo including ex-sherry casks!” But as you can see, no such conclusion can be made.
As I mentioned above, each cask that makes up a batch will impact the pH and unfortunately, I don’t have the exact cask recipe that makes up each of these whiskies. Aside from Elijah Craig Barrel Proof, which was aged in new, charred American oak, I don’t know much about the casks used for aging these whiskies. How many times was each cask used before this whisky went into it? What size were the casks? How many casks went into each batch? All of these recipes belong to the master blender and guess what… The recipes change for each and every batch! The blender is blending to create consistency between batches and not every 12-year-old ex-bourbon cask or ex-sherry cask tastes the same, so they need to tweak the recipe to make sure each batch tastes the same. This means that two batches of the same exact whiskey most likely have different pHs!
The only conclusion I can make based on my pH measurements is that any type and duration of oak aging reduces the pH of whiskey. This is clear by comparing the aged whiskeys (average pH = 3.75) with the two unaged whiskeys (average pH = 7.55). And along with the results from the papers I’ve mentioned above, we can see that the pH drops very quickly (like within a year of the whiskey being in the barrel). That’s because extraction happens very quickly… just drop a small piece of oak into a jar of whiskey (or any spirit) and watch the color change within a day.
Other Q&A Posts
“What are the different distillation cuts?” When distilling any spirit, there are parts of the distillate that you want to keep and others that you want to toss out. The distillation cuts are commonly referred to as the heads, hearts and tails and they condense off the still in that order. The hearts cut is what the distiller keeps, ages and bottles. Read about the composition of each distillation cut and more here!